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Aims This study aimed to prospect and isolate lactic acid bacteria (LAB) from an artisanal cheese production environment, to assess their safety, and to explore their bacteriocinogenic potential against Listeria monocytogenes. Methods and results Samples were collected from surfaces of an artisanal-cheese production facility and after rep-PCR and 16S rRNA sequencing analysis, selected strains were identified as to be belonging to Lactococcus garvieae (1 strain) and Enterococcus faecium (14 isolates, grouped into three clusters) associated with different environments (worktables, cheese mold, ripening wooden shelves). All of them presented bacteriocinogenic potential against L. monocytogenes ATCC 7644 and were confirmed as safe (γ-hemolytic, not presenting antibiotic resistance, no mucus degradation properties, and no proteolytic or gelatinase enzyme activity). Additionally, cell growth, acidification and bacteriocins production kinetics, bacteriocin stability in relation to different temperatures, pH, and chemicals were evaluated. According to performed PCR analysis all studied strains generated positive evidence for the presence of ent A and ent P genes (for production of enterocins A and enterocins P, respectively). However, pediocin PA-1 associated gene was recorded only in DNA obtained from E. faecium ST02JL and Lc. garvieae ST04JL. Conclusions It is worth considering the application of these safe LAB or their bacteriocins in situ as an alternative means of controlling L. monocytogenes in cheese production environments, either alone or in combination with other antimicrobials. [ABSTRACT FROM AUTHOR]

Aim This study examined Listeria monocytogenes isolates from two slaughterhouses in Burdur province, southern Turkey, over four seasons for antibiotic resistance, serogroups, virulence genes, in vitro biofilm forming capacity, and genetic relatedness. Methods and results Carcass (540) and environment-equipment surface (180) samples were collected from two slaughterhouses (S1, S2) for 1 year (4 samplings). Of the 89 (12.4%) positive isolates, 48 (53.9%) were from animal carcasses, and 41 (46.1%) from the environment-equipment surfaces. Autumn was the peak season for Listeria monocytogenes compared to summer and spring (P  < 0.05). In addition, the most common serotype between seasons was 1/2c. Except for plcA and luxS genes, all isolates (100%) harbored inlA, inlC, inlJ, hlyA, actA, iap, flaA genes. Listeria monocytogenes isolates were identified as belonging to IIc (1/2c-3c; 68.5%), IVb (4b-4d-4e; 29.2%), and IIa (1/2a-3a; 2.2%) in the screening using multiplex polymerase chain reaction-based serogrouping test. A total of 65 pulsotypes and 13 clusters with at least 80% homology were determined by using pulsed field gel electrophoresis on samples that had been digested with ApaI. Thirty-four (38.2%) of the isolates were not resistant to any of the 14 antibiotics tested. The antibiotic to which the isolates showed the most resistance was rifampicin (44.9%). Serotype 1/2c was the most resistant serotype to antibiotics. Despite having biofilm-associated genes (inlA, inlB, actA, flaA , and luxS), a minority (11%) of isolates formed weak biofilm. Conclusion This study revealed seasonal changes prevalence of Listeria monocytogenes , particularly higher in autumn, posing a greater risk of meat contamination. Notably, Serotype 1/2c showed significant prevalence and antibiotic resistance. Indistinguishable isolates indicated cross-contamination, underscoring the importance of prioritized training for slaughterhouse personnel in sanitation and hygiene protocols. [ABSTRACT FROM AUTHOR]

Aim The aim of the current study is to elucidate the inactivation and molecular response pattern of sublethal Listeria monocytogenes to cold plasma-mediated two-pronged oxidative microenvironments from a high-throughput multi-omics perspective. Methods and results First joint transcriptomics and metabolomics analyses revealed that significantly expressed genes and metabolites were mainly involved in enhanced transmembrane transport and Fe2+/Cu+ efflux, amino acid limitation, cytoplasmic pH homeostasis, reconfiguration of central carbon metabolism flux, and energy conservation strategy, which triggered the surge of intracellular endogenous oxidative stress and finally mediated bacterial ferroptosis and pathogenicity attenuation. Typical antioxidant systems such as the TrxR-Trx system and common antioxidant genes (e.g. sodA, katA, ahpC, trxA, spxA) were inhibited, and the more prominent antioxidant pathways include methionine metabolism, the pentose phosphate pathway, and glutathione metabolism, as well as the DNA repair systems. Conclusions Therefore, our work confirmed from the transcriptional and metabolic as well as physiological levels that cold plasma-mediated intracellular oxidative stress induced big perturbations in pathways as a driving force for the inactivation and pathogenicity attenuation of L. monocytogenes.     Significance and impact of study This study provided new insights for the construction of multi-dimensional mechanisms of bacterial inactivation and pathogenicity attenuation for the precise control and inactivation of microorganisms in plasma non-thermal processing. [ABSTRACT FROM AUTHOR]

Aims PgpH gene has an important regulatory role on bacterial physiological activity, but studies on its regulation mechanism on biofilm formation of Listeria monocytogenes are lacking. Our aim was to investigate the effect of pgpH gene deletion on biofilm formation in L. monocytogenes. Methods and results The Δ pgpH deletion strain of L. monocytogenes LMB 33  426 was constructed by homologous recombination. Deletion of the pgpH gene resulted in a significant reduction in biofilm formation. The swimming ability of the Δ pgpH strain on semisolid plates was unchanged compared to the wild-type strain (WT), and the auto-aggregation capacity of L. monocytogenes was decreased. RNA-seq showed that Δ pgpH resulted in the differential expression of 2357 genes compared to WT. pgpH inactivation resulted in the significant downregulation of the cell wall formation-related genes dltC, dltD, walK , and walR and the flagellar assembly related genes fliG and motB. Conclusions This study shows that the deletion of pgpH gene regulates biofilm formation and auto-aggregation ability of L. monocytogenes by affecting the expression of flagellar assembly and cell wall related genes. pgpH has a global regulatory effect on biofilm formation in L. monocytogenes. [ABSTRACT FROM AUTHOR]

Aims: The aim of the current study was to investigate the effect of plasma‐mediated oxidative stress on the post‐treatment viability of Listeria monocytogenes at the physiological and molecular levels. Methods and Results: 107 CFU/ml L. monocytogenes in 10 ml phosphate‐buffered saline (PBS) was treated with atmospheric non‐thermal plasma for 0, 30, 60, 90 and 120 s respectively. Optical diagnostics using optical emission spectroscopy (OES) confirmed that dielectric barrier discharge (DBD) plasma was a significant source of ample exogenous reactive oxygen and nitrogen species (RONS). The development of extracellular main long‐lived species was associated with plasma exposure time, accompanied by a massive accumulation of intracellular ROS in L. monocytogenes (p < 0.01). With the exception of virulence genes (hly), most oxidation resistance genes (e.g. sigB, perR, lmo2344, lmo2770 and trxA) and DNA repair gene (recA) were upregulated significantly (p < 0.05). A visible fragmentation in genomic DNA and a decline in the secretion of extracellular proteins and haemolytic activity (p < 0.01) were noticed. The quantitate oxygen consumption rates (OCRs) and extracellular acidification rates (ECARs) confirmed the viability attenuation from the aspect of energy metabolism. Survival assay in a real food system (raw milk) further suggested not only the viability attenuation, but also the resuscitation potential and safety risk of mild plasma‐treated cells during post‐treatment storage. Conclusion: DBD plasma had the potential to inactivate and attenuate the virulence of L. monocytogenes, and it was recommended that plasma exposure time longer than 120 s was more suitable for attenuating viability and avoiding the recovery possibility of L. monocytogenes in raw milk within 7 days. Significance and Impact of the Study: The current results presented a strategy to inactivate and attenuate the viability of L. monocytogenes, which could serve as a theoretical basis for better application of non‐thermal plasma in food in an effort to effectively combat foodborne pathogens. [ABSTRACT FROM AUTHOR]

Aim: To isolate the slow‐growing or viable but non‐culturable competitive exclusion (CE) microorganisms from composts and then verify the anti‐Listeria monocytogenes activities of those CE isolates in compost. Methods and Results: CE strains were isolated from composts using double‐ or triple‐layer agar methods, purified, and then characterized. Both compost extracts and solid compost samples were spiked with a cocktail of 3 L. monocytogenes strains which were co‐inoculated with or without CE strain cocktail and incubated at both 22 and 35°C for 168 h. Results indicated that the addition of resuscitation promoting factor (Rpf) promoted the growth of slow‐growing species from composts. About 50% of the isolated CE strains (n = 40) were identified as Bacillus spp., 17 strains can inhibit more than 10 tested L. monocytogenes strains, and nine strains were motile and competitive biofilm formers. In compost extracts, the growth potentials of L. monocytogenes were reduced up to 2.2 logs when co‐culturing with CE strains. In compost samples, the addition of CE strains reduced L. monocytogenes population by ca. 1.3 log CFU/g at 22°C after 24–168 h incubation. Conclusion: Our modified double/triple‐layer agar procedure with Rpf as growth supplement coupled with spot‐on‐lawn testing can be a quick and efficient method for isolating CE candidates from composts. The efficacy of CE strains against L. monocytogenes in compost extracts and compost samples was affected by compost type, nutrient level, and incubation temperature. Significance and Impact of the Study: Compost is a rich source of CE microorganisms, and compost‐adapted CE microorganisms have the potential as a biological agent to control L. monocytogenes in agricultural environments. [ABSTRACT FROM AUTHOR]

Aims: This study explored how dairy farm operating systems with free‐stall or tie‐stall housing and cow hygiene score influence the occurrence of zoonotic bacteria in raw milk. Methods and Results: Samples from bulk tank milk (BTM), milk filters, faeces, feed, teats and teat milk were collected from 11 farms with loose housing and seven farms with tie‐stall housing every second month over a period of 11 months and analysed for the presence of STEC by culturing combined with polymerase chain reaction and for Campylobacter spp. and L. monocytogenes by culturing only. Campylobacter spp., L. monocytogenes and STEC were present in samples from the farm environment and were also detected in 4%, 13% and 7% of the milk filters, respectively, and in 3%, 0% and 1% of BTM samples. Four STEC isolates carried the eae gene, which is linked to the capacity to cause severe human disease. L. monocytogenes were detected more frequently in loose housing herds compared with tie‐stalled herds in faeces (p = 0.02) and feed (p = 0.03), and Campylobacter spp. were detected more frequently in loose housing herds in faeces (p < 0.01) and teat swabs (p = 0.03). An association between cow hygiene score and detection of Campylobacter spp. in teat milk was observed (p = 0.03). Conclusion: Since some samples collected from loose housing systems revealed a significantly higher (p < 0.05) content of L. monocytogenes and Campylobacter spp. than samples collected from tie‐stalled herds, the current study suggests that the type of housing system may influence the food safety of raw milk. Significance and Impact of the Study: This study highlights that zoonotic bacteria can be present in raw milk independent of hygienic conditions at the farm and what housing system is used. Altogether, this study provides important knowledge for evaluating the risk of drinking unpasteurized milk. [ABSTRACT FROM AUTHOR]

Aims: To reveal the antibacterial mechanism of the combination of thymol and cinnamaldehyde to Listeria monocytogenes ATCC 19115 on autoclaved chicken breast. Methods and Results: In this study, L. monocytogenes ATCC 19115 on autoclaved chicken breast was exposed to the stress of 125 μg/ml thymol and 125 μg/ml cinnamaldehyde, and transcriptome analysis was used to reveal the crucial antibacterial mechanism. According to the results, 1303 significantly differentially expressed genes (DEGs) were identified. Treated by thymol and cinnamaldehyde in combination, pyrimidine and branched‐chain amino acid biosynthesis of L. monocytogenes were thwarted which impairs its nucleic acid biosynthesis and intracellular metabolism. The up‐regulated DEGs involved in membrane composition and function contributed to membrane repair. Besides, pyruvate catabolism and TCA cycle were restrained which brought about the disturbance of amino acid metabolism. ABC transporters were also perturbed, for instance, the uptake of cysteine, D‐methionine, and betaine was activated, while the uptake of vitamin, iron, and carnitine was repressed. Thus, L. monocytogenes tended to activate PTS, glycolysis, glycerol catabolism, and pentose phosphate pathways to obtain energy to adapt to the hostile condition. Noticeably, DEGs involved in virulence factors were totally down‐regulated, including genes devoted to encoding flagella, chemotaxis, biofilm formation, internalin as well as virulence gene clusters. Conclusions: The combination of thymol and cinnamaldehyde is effective to reduce the survival and potential virulence of L. monocytogenes on autoclaved chicken breast. Significance and Impact of Study: This work contributes to providing theoretical information for the application and optimization of thymol and cinnamaldehyde in ready‐to‐eat meat products to inhibit L. monocytogenes. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to compare the efficacy of plasma‐activated water (PAW) generated by two novel plasma reactors against pathogenic foodborne illness organisms. Methods and results: The antimicrobial efficacy of PAW produced by a bubble spark discharge (BSD) reactor and a dielectric barrier discharge‐diffuser (DBDD) reactor operating at atmospheric conditions with air, multiple discharge frequencies and Milli‐Q and tap water, was investigated with model organisms Listeria innocua and Escherichia coli in situ. Optimal conditions were subsequently employed for pathogenic bacteria Listeria monocytogenes, E. coli and Salmonella enterica. DBDD‐PAW reduced more than 6‐log of bacteria within 1 min. The BSD‐PAW, while attaining high log reduction, was less effective. Analysis of physicochemical properties revealed that BSD‐PAW had a greater variety of reactive species than DBDD‐PAW. Scavenger assays designed to specifically sequester reactive species demonstrated a critical role of superoxide, particularly in DBDD‐PAW. Conclusions: DBDD‐PAW demonstrated rapid antimicrobial activity against pathogenic bacteria, with superoxide the critical reactive species. Significance and impact of study: This study demonstrates the potential of DBDD‐PAW produced using tap water and air as a feasible and cost‐effective option for antimicrobial applications, including food safety. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to evaluate the effectiveness of selected essential oils (EOs) and hydrolates (Hs) against Listeria monocytogenes biofilms on polystyrene (PS) and stainless steel (SS) surfaces. Methods and Results: Among others, Origanum hirtum EO, Corydothymus capitatus EO and Citrus aurantium H were selected to treat L. monocytogenes biofilms during and after biofilm formation. Sub‐minimum inhibitory concentrations (MICs) of C. capitatus EO (0.31 µl/ml) showed the highest inhibiting effect against biofilm formation on PS, while on SS no significant differences between the EOs were observed (43.7%–88.7% inhibition). Overall, the tested biosanitizers showed limited activity as biofilm removal agents. Although generally less effective, C. aurantium H exhibited good biofilm inhibition performance at 62.5 µl/ml, particularly on PS. Confocal laser scanning microscopy proved that sub‐MICs of the biosanitizers drastically changed L. monocytogenes biofilm architecture, with bacterial cells elongation in the presence of C. capitatus EO. Conclusions: Our findings suggest that the tested EOs and H are able to control Listeria biofilms, particularly preventing biofilm formation on both materials. Considering its mild aroma and hydrophilicity, the H exhibited promising perspectives of application. Significance and Impact of Study: This study raises the possibility of applying EOs and Hs to control biofilms on different surfaces in the food industry. [ABSTRACT FROM AUTHOR]

Aims: To investigate the potential of novel Bacillus velezensis P45 as an eco‐friendly alternative for bioprocessing poultry by‐products into valuable antimicrobial products. Methods and Results: The complete genome of B. velezensis P45 was sequenced using the Illumina MiSeq platform, showing 4455 protein and 98 RNA coding sequences according to the annotation on the RAST server. Moreover, the genome contains eight gene clusters for the production of antimicrobial secondary metabolites and 25 putative protease‐related genes, which can be related to feather‐degrading activity. Then, in vitro tests were performed to determine the production of antimicrobial compounds using feather, feather meal and brain–heart infusion (BHI) cultures. Antimicrobial activity was observed in feather meal and BHI media, reaching 800 and 3200 AU ml−1 against Listeria monocytogenes respectively. Mass spectrometry analysis indicates the production of antimicrobial lipopeptides surfactin, fengycin and iturin. Conclusions: The biotechnological potential of B. velezensis P45 was deciphered through genome analysis and in vitro studies. This strain produced antimicrobial lipopeptides growing on feather meal, a low‐cost substrate. Significance and Impact of Study: The production of antimicrobial peptides by this keratinolytic strain may represent a sustainable alternative for recycling by‐products from poultry industry. Furthermore, whole B. velezensis P45 genome sequence was obtained and deposited. [ABSTRACT FROM AUTHOR]

Aims: The biological events occurring during human digestion help to understand the mechanisms underlying the dose–response relationships of enteric bacterial pathogens. To better understand these events, we investigated the growth and reduction behaviour of bacterial pathogens in an in vitro model simulating the environment of the small intestine. Methods and Results: The foodborne pathogens Campylobacter jejuni, Listeria monocytogenes and Escherichia coli O157:H7 were cultured with multiple competing enteric bacteria. Differences in the pathogen's growth kinetics due to the relative amount of competing enteric bacteria were investigated. These growth differences were described using a mathematical model based on Bayesian inference. When pathogenic and enteric bacteria were inoculated at 1 log CFU per ml and 9 log CFU per ml, respectively, L. monocytogenes was inactivated over time, while C. jejuni and E. coli O157:H7 survived without multiplying. However, as pathogen inocula were increased, its inhibition by enteric bacteria also decreased. Conclusions: Although the growth of pathogenic species was inhibited by enteric bacteria, the pathogens still survived. Significance and Impact of the Study: Competition experiments in a small‐intestine model have enhanced understanding of the infection risk in the intestine and provide insights for evaluating dose–response relationships. [ABSTRACT FROM AUTHOR]

Aim: To detect and characterize novel lantibiotics from a collection of Bacillus spp. using a multifaceted analytical approach. Methods and Results: A previously completed microassay identified 45 Bacillus isolates with anti‐Listeria activity. The isolates were PCR screened using degenerate primers targeting conserved sequences in lanM‐type lantibiotics. B. velezensis GF610 produced a PCR product whose sequence, along with genome mining and bioinformatics, guided the liquid chromatographic analysis of strain's cell‐free extracts and the mass spectrometry of purified fractions. Results revealed a new amyloliquecidin variant (designated GF610) produced by the strain. Amyloliquecidin GF610 is a two‐component lantibiotic with α and β peptides having monoisotopic masses of 3026 and 2451 Da, and molecular formulae C130H191N35O39S5 and C110H158N26O30S4, respectively. Amyloliquecidin GF610 is active against Listeria monocytogenes, Clostridium sporogenes, Clostridioides difficile, Staphylococcus aureus and Alicyclobacillus acidoterrestris with minimum inhibitory concentrations (MICs) in the range of 0.5–7.0 µmol l–1. Conclusions: The proposed multifaceted analytical approach was valuable to provide a deep and proper characterization of a novel bacteriocin, amyloliquecidin GF610, with high antimicrobial activity against Gram‐positive bacteria. Significance and Impact: The discovered Amyloliquecidin GF610 is potentially useful in food, agricultural or medical applications. The analytical approach followed may facilitate future discoveries of two‐component lantibiotics, which are challenging compounds to detect and characterize. [ABSTRACT FROM AUTHOR]

Aim: The study aimed to investigate the role of cattle slaughterhouse wastewater as a possible source for the environmental distribution of Listeria monocytogenes. Methods and Results: Listeria spp. isolation was performed by collecting 117 wastewater samples from four different cattle slaughterhouses in Turkey. Species‐specific identification was performed biochemically, and L. monocytogenes isolates were confirmed with polymerase chain reaction (PCR). In all, 71 (62.2%) of the wastewater samples were found to be positive for Listeria spp., and 17 (14.9%) of these samples were contaminated with L. monocytogenes. Pulsed field gel electrophoresis (PFGE) analysis revealed that all L. monocytogenes isolates were of different pulsotypes and isolates belonged to seven different phylogenetic clusters. Multiplex PCR analysis for genoserotypes and lineage determination showed that the isolates were divided into genoserotypes IVb and IIc in Lineages I and II. Also, it has been investigated with SYBR‐Green Real‐time PCR whether the L. monocytogenes isolates harboured virulence genes (hly, sigB, plcA, plcB, inlA, inlB, inlC and inlJ), and it was found that all isolates were substantially positive. Antibiotic resistance profiles and MIC values of the isolates were determined, and all L. monocytogenes isolates were found susceptible to ampicillin. In contrast, two isolates were resistant to meropenem and erythromycin, and three isolates were resistant to trimethoprim/sulfamethoxazole. Conclusion: L. monocytogenes, which pose a threat to public health and resists to antibiotics effectively used in treatments, can environmentally spread via wastewater of cattle slaughterhouses. The wastewater of the food industry, which has rich microbiota, should be treated carefully, and possible environmental contamination should be prevented. Significance and Impact of Study: This is the first study that investigates the molecular characterization of L. monocytogenes isolated from cattle slaughterhouse wastewater and the findings represent the importance of cattle wastewater in the epidemiology of L. monocytogenes in Turkey. [ABSTRACT FROM AUTHOR]

Aims: The two‐parameter (α and β) Schiraldi's model reliably fits growth curves of psychrotrophic pathogens and suggests a different description of the latency phase. Methods and Results: Data obtained at various temperatures and different starting cell densities for Aeromonas hydrophila, Listeria monocytogenes and Yersinia enterocolitica have been fitted with the Baranyi and Roberts' model and the new one. On average, the former showed higher standard error and R2 values (0.140 and 0.991) than the Schiraldi's one (0.079 and 0.983). Around 15℃, the increase of temperature showed a milder effect on the growth rate than that expected. Y. enterocolitica showed a practically null duration of the lag phase, no matter the value of the starting density, whereas A. hydrophila and L. monocytogenes revealed slower onset trends. Conclusions: Parameter β defines the number of cell duplications and appears independent on temperature, while (β/α)1/2 is proportional to the maximum specific growth rate. The α−1/2versus temperature trend directly reflects the corresponding behaviour of the growth rate and does not require the use of Arrhenius plots. Significance and Impact of the Study: Values of the parameters α and β, as well as the duration of the latency phase, allowed some considerations about the effect of storage temperature in terms of food safety, especially for psychrotrophic bacteria of concern. [ABSTRACT FROM AUTHOR]

Aims: The objective of this study was to isolate multifunctional bacteriocin‐producing strains; to characterize the expressed bacteriocin for the control of Listeria monocytogenes and vancomycin‐resistant Enterococcus; to evaluate the safety of studied strains; and to explore their antifungal activity. Methods and Results: Two Pediococcus strains were isolated from silage samples obtained from an organic farm in Belogradchik, Bulgaria. The strains were identified by 16S rRNA sequencing analysis and characterized as bacteriocins producers. Strong antimicrobial activity was detected against more than 74 different strains of Listeria monocytogenes, 27 different vancomycin‐resistant Enterococcus strains. In addition, studied strains were able to inhibit the growth of strains of Alternaria alternate, Aspergillus flavus, Aspergillus niger, Cladosporium sphaerospermum, Penicillium chrysogenum and Penicillium expansum. Some aspects of the antimicrobial mode of action were evaluated, including killing curves and aggregation properties. Both strains generated positive PCR results for the presence of pediocin PA‐1, but not for other bacteriocins evaluated in this screening process. Metabolomic analysis of the cell‐free supernatants from both strains was performed in order to explain the observed antifungal activity against different moulds. According to PCA and PLS‐DA score plot, P. acidilactici ST3522BG and P. pentosaceus ST3633BG were clearly clustered from control (MRS). Increases in the production of benzoic acid, 2‐hydroxyisocaproic acid, β‐phenyl‐lactic acid, α‐hydroxybutyric acid and 1,3‐butanediol were recorded, these metabolites were previously described as antifungal. Conclusions: Pediococcus acidilactici ST3522BG and P. pentosaceus ST3633BG were evaluated as producing bacteriocin strains with high specificity against Listeria and vancomycin‐resistant Enterococcus species. In addition, both investigated Pediococcus strains were evaluated as producer of effective antifungal metabolites with potential for the inhibition of mycotoxin‐producing moulds. Significance and Impact of the Study: To the best of our knowledge, this report is a pioneer in the evaluation of Pediococcus strains isolated from silage with highly specific bacteriocinogenic antimicrobial activity against Listeria spp. and vancomycin‐resistant Enterococcus spp., and antifungal activity against mycotoxin‐producing moulds. [ABSTRACT FROM AUTHOR]

Aims: The purpose of this study was to detect growth enhancing or inhibiting activity between bacterial populations from raw milk under different conditions (temperature, medium). Methods and Results: The interference of 24 raw milk isolates on growth of each other and on Listeria monocytogenes, Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus was screened by drop assay and for selected pairs in co‐cultivation experiments. By drop assay, antibacterial activity was observed for 40% of the strains. About 30% of the strains showed growth‐enhancing activity on other strains. Most of the isolates were well adapted to cold temperatures and showed consistent or even increased inhibiting or enhancing effects on growth of other strains at 10°C. The growth of L. monocytogenes DSM 20600T and S. aureus DSM 1104T was significantly (P < 0·05) reduced in co‐cultivation with Pseudomonas protegens JZ R‐192. Conclusions: Growth interferences between bacterial populations have an impact on the structure of raw milk microbiota, especially when it develops under cold storage, and it may have an effect on the prevalence of certain foodborne pathogens. Significance and Impact of the Study: This study demonstrates growth‐inhibiting and also growth‐enhancing interactions between raw milk bacteria, which must be considered when predicting bacterial growth and spoilage in food. A Ps. protegens strain isolated from raw milk showed an antagonistic effect on growth of L. monocytogenes in refrigerated raw milk. [ABSTRACT FROM AUTHOR]

Aims: The objective of this study was to isolate a bacteriocin‐producing strain and to characterize the expressed bacteriocin for the control of Listeria monocytogenes with aim of biopreservation application. Methods and Results: Soil samples from a Korean organic farm were subjected to microbiological analysis for isolation of potential bacteriocinogenic LAB, based on a three‐level approach, using L. monocytogenes ATCC 15313 as an indicator test micro‐organism. From a total of 17 isolates with inhibitory potential, seven were confirmed to be bacteriocin producers. The selected isolates were differentiated based on their morphology, catalase reaction, sugar fermentation profile obtained by API50CHL and by RAPD‐PCR generating two unique profiles. One of the isolates, ST110LD, a specific strong producer of anti‐Listeria bacteriocins (12 800 AU ml−1) was identified as Leuconostoc citreum. The proteinaceous nature of the inhibitory compound produced by Leuc. citreum ST110LD was confirmed through treatment with pepsin and α‐chymotrypsin. Bacteriocin activity was observed to be not affected by the presence of milk, NaCl, SDS, Tween 80 or glycerol. Bacteriocin ST110LD effectively inhibited the growth of exponentially growing L. monocytogenes ATCC 15313 during a 10‐h incubation period in BHI at 37°C. In addition, this bacteriocin showed specific inhibition of only Listeria spp., but did not inhibit the growth of beneficial cultures included in the microbial test panel for assessment of the spectrum of activity. Conclusions: Leuconostoc citreum ST110LD was evaluated as safe bacterium strain, producing bacteriocin with high specificity against listerial and enterococcal species. Specificity of producer strain and expressed bacteriocin can be explored in biopreservation of different fermented food products or applied in biotherapy of antibiotic resistant listerial or enterococcal infections. Significance and Impact of the Study: To the best of our knowledge, this is the first report of bacteriocin produced by Leuc. citreum strain with highly specific antimicrobial activity against Listeria sp. and Enterococcus sp. [ABSTRACT FROM AUTHOR]

Aims: In this study, benzalkonium chloride (BAC) microcapsules were developed for surface disinfection purpose and were evaluated against Listeria monocytogenes and Escherichia coli biofilms. Methods and Results: Microcapsules were prepared with two different strategies: uncomplexed BAC‐microcapsules (UBM) containing BAC and maltodextrins, and complexed BAC‐microcapsules (CBM) containing BAC complexed by pectin and maltodextrins. The minimum inhibitory concentrations (MICs) of free and microencapsulated BAC were investigated against two food pathogens: L. monocytogenes and E. coli. The antibiofilm activities of UBM and CBM against L. monocytogenes and E. coli biofilms formed on stainless steel at 37°C were evaluated and compared to BAC used under its free form. MICs of encapsulated BAC were up to fourfold lower than those of free BAC. The UBM and CBM showed higher antibiofilm effect when compared to the free BAC. Conclusions: Overall, results demonstrated that microencapsulation enhanced the antibacterial activity of BAC against L. monocytogenes and E. coli biofilms. Significance and Impact of the Study: The application of such BAC microcapsule‐based delivery systems can improve surface disinfection procedures and reduce the required BAC concentrations and the related cytotoxicity of this antimicrobial compound. [ABSTRACT FROM AUTHOR]

Aims: To investigate the effects of the lectin from Punica granatum sarcotesta (PgTeL) on growth, viability, cell structure, biofilm formation and chitinase activity of Listeria monocytogenes. In addition, the effect of PgTeL on the adhesion and invasion of human cells (HeLa) was determined. Methods and Results: PgTeL showed bacteriostatic and bactericidal effects on the strains L. monocytogenes N53‐1 and EGD‐e, causing morphometric alterations, cell aggregation, strong deformation and cell disruption. PgTeL inhibited biofilm formation by EGD‐e and N53‐1 and also interfered with the adhesion and invasion processes of EGD‐e and N53‐1 in HeLa cells. Finally, the chitinase activity of L. monocytogenes EGD‐e was reduced in the presence of PgTeL, which can be involved in the inhibition of adhesion process. Conclusion: PgTeL is an antibacterial agent against L. monocytogenes, inhibiting growth and promoting cell death, as well as impairing biofilm formation and bacterial adhesion and invasion into human cells. Significance and Impact of the Study: The results stimulate future investigations on the potential of PgTeL for protection of contamination in food products. [ABSTRACT FROM AUTHOR]

Aim: To study the impact of incorporating micro‐nano‐bubbles (MNBs) in commonly used food antimicrobials (AMs) against Escherichia coli O157:H7 (EC) and Listeria monocytogenes (LM). Methods and Results: Air, carbon dioxide (CO2) and nitrogen (N2) were used to incorporate MNBs in city water. AM solution (with or without MNBs) of 9 ml was individually taken into sterile test tubes and mixed with 1 ml of inoculum grown in brain heart infusion (BHI) broth to get the net AM concentrations of 28·4 ppm peracetic acid (PAA), 200 ppm chlorine (Cl2), 5·4% citric acid (CA) and 4·5% lactic acid (LA). After treatment time of 1·5 and 3·0 min, 1 ml of sample was neutralized using Dey–Engley neutralizing broth and plated on BHI agar. For EC, Cl2‐CO2 solutions resulted in significantly greater log reductions (5·2 logs) compared to that of Cl2 solutions without MNBs (3·8 logs). For LM, PAA‐CO2 solutions resulted in significantly greater log reductions (4·4 logs) compared to that of PAA solutions without MNBs (1·7 logs). Conclusions: This study demonstrated that the efficacy of Cl2 and PAA AM solutions could be increased by incorporating CO2‐MNBs against EC and LM in microbiological growth medium. Significance and Impact of the Study: Incorporation of CO2‐MNBs in AM solutions could increase the efficacy of AMs against pathogens on/in food matrices, which should be tested in future research. [ABSTRACT FROM AUTHOR]

Aims: The aim of this study was to test the efficacy of new and currently used biocides in the mushroom industry for inactivating Listeria monocytogenes biofilm. Methods and results: A laboratory‐scale study was initially carried out to test the efficacy of eleven biocidal products against a cocktail of five L. monocytogenes strains that were grown to 3‐day biofilms on stainless steel coupons. Biocidal efficacy was then tested under clean and dirty conditions based on the EN 13697:2015 method. The results for the biocides tested ranged between 1·7‐log and 6‐log reduction of biofilm, with only the efficacy of the sodium hypochlorite‐based biocide being significantly reduced in dirty conditions. A pilot‐scale trial was then carried out on a subset of biocides against L. monocytogenes on concrete floors in a mushroom growing room and it was found that biocide efficacy in laboratory‐scale did not translate well in pilot‐scale. Conclusions: Biocides that are used in the mushroom industry and potential alternative biocides were determined to be effective against L. monocytogenes biofilm in both laboratory‐scale and pilot‐scale experiments. Significance and Impact of the Study: This study has direct impact for the industry as it provides information on the efficacy of currently used biocides and other biocidal products against L. monocytogenes, an added benefit to their primary use. [ABSTRACT FROM AUTHOR]

Aims: To understand the genetics involved in surface attachment and biofilm formation of Listeria monocytogenes. Methods and Results: An in vitro screen of a Himar1 transposon library of L. monocytogenes strain 15G01 identified three transposants that produced significantly different biofilm levels when compared to the wild‐type strain; two mutants exhibited enhanced biofilm formation and one produced less biofilm biomass than the wild‐type. The mutant 15G01 mprF::Himar1, which had a transposon insertion in the mprF gene, was selected for further analysis. The mutant produced a more densely populated biofilm on solid surfaces such as stainless steel and polystyrene, as determined using scanning electron and light microscopy. The 15G01 mprF::Himar1 mutant remained viable in biofilms, but showed an increase in sensitivity to the cationic antimicrobial gallidermin. The mutant also displayed reduced invasiveness in CaCo‐2 intestinal cells, suggesting virulence properties are compromised by the inactivation of mprF. Conclusions: Biofilm formation and gallidermin resistance of L. monocytogenes is influenced by mprF, but this trait is associated with a compromise in invasiveness. Significance and Impact of the Study: The presence of pathogenic microorganisms in the food processing environment can cause a significant problem, especially when these microorganisms are established as biofilms. This study shows that the inactivation of the mprF gene results in enhanced biofilm formation and abiotic surface attachment of L. monocytogenes. [ABSTRACT FROM AUTHOR]

Aims: This study measured the survival of Listeria monocytogenes and Salmonella enterica subsp. enterica serovar Javiana over a 10‐day period on four soil‐free cultivation matrix (SFCM) types in the absence of microgreens and fertilizers. Methods and Results: Coco coir (CC), a Sphagnum peat/vermiculite mix, Biostrate® and hemp mat samples were inoculated with 3 × 106 CFU per ml bacteria, incubated at room temperature, and analysed on day 0, 1, 3, 6, and 10. Statistically significant differences in pathogen survival were observed across multiple time points for hemp and Biostrate compared to CC, peat and bacteria in phosphate buffered saline (PBS) (P < 0·05). S. Javiana showed greater overall survival compared to Listeria (P < 0·0002). By day 10, S. Javiana persisted at the initial inoculum concentration for hemp and Biostrate while declining by 1–2 log CFU per ml in CC, peat and PBS. Listeria also persisted at the initial concentration in hemp and Biostrate but decreased to 1 log CFU per ml in peat and below the detection limit in CC and PBS. Conclusions: Overall, there are survival differences between bacterial pathogens in SFCM used in microgreen production systems. To our knowledge, this is the first comparison of survival among SFCM involving a S. enterica serovar and L. monocytogenes, and the first study comparing CC, Biostrate and hemp. Significance and Impact of the Study: Microgreens production systems predominantly utilize soil alternatives, and it is not well‐understood how pathogen transmission risk may be affected by the type of SFCM. The results of this study impact the microgreen industry as media selection may be used to reduce the risk of bacterial pathogen proliferation and transmission to the plant potentially resulting in potential foodborne illness. [ABSTRACT FROM AUTHOR]

Aims: Exposure of Listeria monocytogenes to osmotic stress can induce increased resistance to subsequent lethal exposure to cell envelope stressors, such as nisin and bile salts. We wanted to determine if similar cross‐protection phenotypes could occur when L. monocytogenes strains were treated with osmotic stress and exposed to sublethal levels of the cell envelope stressor, bile. Method and Results: Growth phenotypes were measured for six L. monocytogenes strains exposed to 6% NaCl, 0·3 and 1% bile in BHI. To evaluate cross‐protection, cells were pre‐exposed to 6% NaCl, followed by exposure to BHI+1% bile for 26 h and vice versa. Significant increases in λ (lag phase) and doubling time were observed under salt and bile stresses compared with BHI alone. Average λ and Nmax (maximum cell density) in 0·3 and 1% bile for all strains were significantly lower than that in 6% NaCl. Pre‐exposure to 6% NaCl followed by exposure to 1% bile significantly increased λ (P < 0·05), whereas pre‐exposure to 1% bile followed by exposure to 6% NaCl led to formation of filamentous cells, with no changes in cell density over 26 h. Conclusions: Variation in growth characteristics was observed among strains exposed to bile. Exposure to osmotic stress did not lead to increased resistance to bile. Exposure to bile significantly impacted the ability of L. monocytogenes to adapt to grow under osmotic stress, where cells did not multiply but formed filamentous cells. Significance and Impact of the Study: Pre‐exposure to a cell envelope stress and subsequent exposure to an osmotic stress appears to pose a significant stress to L. monocytogenes cells. [ABSTRACT FROM AUTHOR]

Aims: To study the antimicrobial agents of the Bacillus velezensis strain HC6 and assess the application potential of B. velezensis HC6 in maize. Methods and Results: We applied a dual culture technique to test the antimicrobial activity of B. velezensis HC6 against bacteria and fungi of common contaminated crops. Bacillus velezensis HC6 showed antagonistic action on pathogenic fungi, including Aspergillus and Fusarium, as well as pathogenic bacteria (especially Listeria monocytogenes). When applied in maize, B. velezensis HC6 could also inhibit the growth of multiple pathogenic fungi and reduce their production of aflatoxin and ochratoxin. Three kinds of antimicrobial lipopeptides, including iturin, fengycin and surfactin were identified in B. velezensis HC6 culture supernatant by high‐performance liquid chromatography and MALDI‐TOF mass spectrometry. Iturin and fengycin showed obvious antimicrobial activity to the tested fungal strains. Conclusions: Bacillus velezensis HC6 produces three kinds of lipopeptides which showed antimicrobial activity against several common pathogenic fungi and bacteria. Bacillus velezensis HC6 is potential to be biocontrol bacteria in maize. Significance and Impact of the Study: Bacillus velezensis HC6 shows obvious antimicrobial activity to important crops pathogenic fungi which usually produce mycotoxins that are harmful to animal and human health. We demonstrate that three different types of lipopeptides produced by B. velezensis contributed to the antimicrobial activity. Bacillus velezensis HC6 has the potential to be effective biocontrol agent in crops. [ABSTRACT FROM AUTHOR]

Aims: The aim of this study was to develop a rapid detection and differentiation method for pathogenic Listeria species in stone fruits. Methods and Results: We utilized activated charcoal enrichment media (ACM) to induce overexpression and hypersecretion of pathogenic Listeria virulence proteins which can subsequently be detected via immunoblot analysis. Plum and nectarine slices spiked with either L. monocytogenes or L. ivanovii were incubated in pre‐enrichment broth followed by enrichment in ACM. Secreted proteins were precipitated and subjected to SDS‐PAGE and immunoblot analysis using a combination of L. monocytogenes‐specific antibody (α‐listeriolysin O) and antibody specific for both L. monocytogenes and L. ivanovii (α‐Internalin C). As low as 1 CFU per gram of L. monocytogenes in plum and nectarine was detected, whereas a detection limit of 10 CFU per gram was achieved for L. ivanovii in each food tested following a 20‐h enrichment period. Nonpathogenic Listeria species and non‐Listeria bacterial pathogens tested were negative. Conclusions: These results demonstrate the highly sensitive and specific nature of the detection method for pathogenic Listeria in stone fruits using activated charcoal enrichment as well as the capability to discriminate between L. monocytogenes and L. ivanovii. Significance and Impact of the Study: This method is the first to identify and differentiate L. monocytogenes and L. ivanovii in select stone fruit enrichments within 24 h using immunological techniques. The rapidity and sensitivity of the method could aid in the reduction of exposure to the public in the event of an outbreak and expedite the administration of appropriate antibiotics to infected individuals. [ABSTRACT FROM AUTHOR]

Aims: An extensive source investigation was conducted on a dairy farm with neurolisteriosis and subclinical mastitis cases to identify infection source and potential transmission routes of Listeria monocytogenes. Methods and Results: A total of 36 L. monocytogenes isolates were obtained from animal clinical cases (neurolisteriosis and udder infection) and the farm environment (silage, faeces, water). Isolates were typed using pulsed‐field gel electrophoresis (PFGE) and whole‐genome sequencing (WGS). Their virulence potential was assessed using the gentamicin protection assay and WGS‐based identification of virulence genes. PFGE and WGS revealed a high genetic diversity of L. monocytogenes. An epidemiological link was confirmed for isolates from (i) several subclinical mastitis cases, (ii) silage and subclinical mastitis cases and (iii) different water sources. The neurolisteriosis isolate belonged to clonal complex (CC) 1, but infection source was not identified. A high occurrence (9/47 cows; 19·1%) of subclinical mastitis was observed with isolates belonging to CC2, CC4 and CC11. Conclusions: The dairy farm environment was contaminated with diverse L. monocytogenes strains, including genotypes associated with human disease. Several isolates harboured genetic determinants associated with increased infectious potential in humans. Significance and Impact of the Study: Results suggest that subclinical listerial mastitis should not be neglected as a potential source of milk contamination. The presence of hypervirulent CCs in subclinical mastitis cases calls for the implementation of improved mastitis detection. [ABSTRACT FROM AUTHOR]

Aims: The control of Listeria monocytogenes biofilm formation using lactocin AL705 bacteriocin at sub‐minimum inhibitory concentrations (MICs) through an antiquorum sensing strategy, was preliminarily investigated. Methods and Results: The screening for biofilm formation of different Listeria species at 10°C allowed selecting L. monocytogenes FBUNT for its use as biofilm producer. MIC and minimum bactericidal concentration of lactocin AL705 purified extract against the pathogen was determined. Bacteriocin sub‐MICs were used to evaluate biofilm reduction. Concentrations between 2·5–20 AU ml−1 of lactocin AL705 produced significant decreases in biofilm formation without affecting the growth of the pathogen after 3 days of incubation. When bacteriocin concentrations (5–20 arbitrary units per millilitre (AU ml−1)) were investigated as quorum sensing (QS) inhibitors using Vibrio harveyi as reporter strain, a significant reduction in luminescence by lactocin AL705 (20 AU ml−1) was observed. Even when L. monocytogenes produced AI‐2 like molecules as recognized by the reporter strain, bacteriocins did not interfere with this compound. Conclusion: Antilisterial lactocin AL705 used to disrupt QS through a signal molecule inactivation was able to control L. monocytogenes FBUNT biofilm formation. Other molecule(s) different from the AI‐2 involved during biofilm formation could be acting as target of the bacteriocin. Significance and Impact of the Study: The use of bacteriocins derived from food‐grade micro‐organisms as a QS inhibition represents an effective strategy to control pathogens as well as an environmentally friendly sanitation method to mitigate postprocessing food contamination. [ABSTRACT FROM AUTHOR]

Aims: The aim of this study was to develop a multiplex touchdown PCR (multiplex TD‐PCR) for rapid and simultaneous detection of four major foodborne pathogens to avoid mispriming and unwanted production during gene amplification. Touchdown PCR is the modified form of standard PCR, which enhances specificity, sensitivity. Methods and Results: For this reason, a multiplex TD‐PCR assay with a pre‐enrichment step was developed to detect four foodborne pathogens namely Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, and Salmonella enterica serovar Enteritidis in pure culture and raw milk samples. The results showed that this protocol can eliminate the unwanted band or reduce significantly. The detection sensitivity of the single and multiplex TD‐PCR was one cell per ml in pure culture. Furthermore, the detection limit of multiplex TD‐PCR was one cell per 25 ml for artificially contaminated raw milk. We obtained similar results for detection of aforementioned pathogens in raw milk, after comparing the multiplex TD‐PCR method with the traditional culture, except in one or two samples. Conclusions: Hence, the proposed multiplex TD‐PCR method could be confirmed as an effective way for rapid optimization of PCR reactions to increase specificity, sensitivity during gene amplification. Significance and Impact of the Study: Hence, due to its simplicity, cost‐effectiveness and being time‐saving, it seems that this method is reasonable and economical for rapid optimization of PCR reactions. [ABSTRACT FROM AUTHOR]

Aim: To investigate the use of a light scattering sensor, BActerial Rapid Detection using Optical scattering Technology (BARDOT) coupled with a multipathogen selective medium, Salmonella, Escherichia and Listeria (SEL), for concurrent detection of the three major foodborne pathogens in a single assay. Methods and Results: BARDOT was used to detect and distinguish the three major pathogens, Salmonella enterica, Shiga toxin‐producing Escherichia coli (STEC) and Listeria monocytogenes from food based on colony scatter signature patterns on SEL agar (SELA). Multiple strains of three test pathogens were grown on SELA, and BARDOT was used to generate colony scatter image libraries for inclusive (SEL Library) and exclusive (non‐SEL Library) bacterial group. These pathogens were further differentiated using the SEL scatter image library. Raw chicken and hotdog samples were artificially inoculated with pathogens (100 CFU per 25 g each), and enriched in SEL broth at 37°C for 18 h and colonies were grown on SELA for 11–22 h before screening with BARDOT. The BARDOT sensor successfully detected and differentiated Salmonella, STEC and Listeria on SELA with high classification accuracy 92–98%, 91–98% and 83–98% positive predictive values (PPV) respectively; whereas the nontarget strains showed only 0–13% PPV. BARDOT‐identified colonies were further confirmed by multiplex PCR targeting inlB gene of L. monocytogenes, stx2 of STEC and sefA of S. enterica serovar Enteritidis. Conclusions: The results show that BARDOT coupled with SELA can efficiently screen for the presence of three major pathogens simultaneously in a test sample within 29–40 h. Significance and Impact of the Study: This innovative SELA‐BARDOT detection platform can reduce turnaround time and economic burden on food industries by offering a label‐free, noninvasive on‐plate multipathogen screening technology for reducing microbial food safety and public health concerns. [ABSTRACT FROM AUTHOR]

Aim: A lectin Concanavalin A (ConA) derived from Canavalia ensiformis (jack bean) exhibits high‐binding affinity to carbohydrates on bacterial cell surfaces. The objective of this study was to inhibit the biofilm formation of the foodborne pathogens enterohemorrhagic Escherichia coli and Listeria monocytogenes using ConA prepared by a membrane‐based extraction method. Methods and Results: ConA was extracted using a simple and inexpensive membrane method instead of a chromatography approach. The extracted ConA was effective in inhibiting biofilms of E. coli by 30‐fold and L. monocytogenes by 140‐fold. In addition, ConA decreased the swimming motility of enterohemorrhagic E. coli EDL933 (EHEC) by 37%, resulting in low biofilm formation, as ConA binding to the bacterial cell surfaces might cause a reduced capability to adhere due to low cellular motility. We confirmed that the extracted ConA contains active components at less than 10 kDa as well as ConA multimers (>30 kDa) that repress EHEC biofilms. Additionally, noncell‐based mannose reduced the activity of ConA in inhibiting biofilms. Conclusions: ConA extracted using the membrane‐based method is active in inhibiting the biofilm formation by E. coli and L. monocytogenes via the mannose‐binding affinity of ConA. Significance and Impact of the Study: ConA can be used as a promising anti‐adherent and antibiofilm agent in inhibiting biofilm formation by enterohemorrhagic E. coli and L. monocytogenes. The membrane‐based extraction approach may be applied for the economic production of biologically active lectins. [ABSTRACT FROM AUTHOR]

Aims: A high resolution melting (HRM) assay was developed for characterizing lineage II Listeria monocytogenes based on the amplification and the melting profiles analysis of 81 fragments targeting the region from the prs to ldh loci, including the Listeria Pathogenicity Island‐1 (LIPI‐1) genes and the inlAB operon. Methods and Results: Real‐time PCR and HRM protocols were standardized using 10 replicate assays from L. monocytogenes EGD‐e reference strain (serovar 1/2a). Twenty wild‐type isolates of serovar 1/2a and two of serovar 1/2c were tested, and differences between EGD‐e strain and the wild‐type isolates were defined if the melting temperature (Tm) of an amplicon was not within the lower and the upper limits calculated from replicate testing on EGD‐e. The analysis revealed 17 and 19 HRM profiles with respect to prs/LIPI‐1/ldh and inlAB target regions (Simpson's Index of Diversity 0·979 and 0·983) respectively. The 1/2c cultures showed 98·1% similarity to melting characteristics with EGD‐e, whilst 1/2a isolates had the greatest heterogeneity that was related to inlA, inlB and actA genes. Sequencing of amplicons generating different Tm values from EGD‐e confirmed the presence of point mutations. Conclusions: This method was useful for L. monocytogenes subtyping based on single nucleotide polymorphisms detection through the melting behaviour analysis of main virulence genes. Significance and Impact of the Study: The study underlines the effectiveness of HRM in differentiating L. monocytogenes strains with high discriminatory power, thus rendering it useful for epidemiological surveillance. [ABSTRACT FROM AUTHOR]

Aims: This research aims to develop strongly adherent and mature model biofilms (on a 20 cm² polystyrene surface) for two pathogenic species, i.e. Listeria monocytogenes and Salmonella Typhimurium. These model biofilms can be used as standards to study biofilms or to study/compare the influence of different inactivation technologies. Methods and Results: Three influencing factors on the formation of biofilms are investigated, i.e. growth medium, incubation temperature and incubation time, which are three easily controllable environmental factors. Optical density measurement and plate counts were used to evaluate the adherence and the maturity of the biofilms, respectively. Confocal laser scanning microscopy was used to verify most important findings obtained with previously mentioned assays. Results indicated that mature and strongly adherent L. monocytogenes biofilms are obtained following 13 h of incubation at 30°C with BHI as growth medium. For S. Typhimurium, an incubation period of 19 h at 25°C was required with 20‐fold diluted TSB as growth medium. Conclusions: Based on previously mentioned assays, a protocol for the formation of reproducible model biofilms was obtained. Significance and Impact of the Study: The developed model biofilms can be applied as a standard to study biofilms (in different research fields) and their subsequent inactivation by different methods. In addition, the results of this study could be used to control biofilm formation (e.g. by setting a maximum allowed surface temperature). [ABSTRACT FROM AUTHOR]

Aims: The objectives of this study were to evaluate the effect of combination treatment with cold plasma (CP), vacuum packaging (VP), and hot water (HW) on the inactivation of foodborne pathogens on buckwheat seeds, and determined the germination rates of seeds and the quality of sprouts following combination treatment., Methods and Results: Buckwheat seeds inoculated with Salmonella Typhimurium and Listeria monocytogenes were treated with CP, HW, CP + HW, VP + HW, or CP + VP + HW. The germination rates of the HW-, CP + HW-, VP + HW-, and CP + VP + HW-treated seeds and the antioxidant activities and rutin contents of the CP + HW- and CP + VP + HW-treated sprouts were determined. HW, CP + HW, and CP + VP + HW were found to reduce the levels of the two pathogens to below the detection limit (1.0 log CFU g-1) at 70°C. However, HW and CP + HW significantly reduced the germination rate of buckwheat seeds. CP + VP + HW did not affect the germination rate of seeds nor the antioxidant activities and rutin content of buckwheat sprouts., Conclusions: These results indicate that CP + VP + HW can be used as a novel control method to reduce foodborne pathogens in seeds without causing quality deterioration., (© The Author(s) 2023. Published by Oxford University Press on behalf of Applied Microbiology International.)

Summary: Listeria monocytogenes is an intracellular human pathogen which enters the body through contaminated food stuffs and is known to contaminate fresh leafy produce such as spinach, lettuce and rocket. Routinely, fresh leafy produce is grown and processed on a large scale before reaching the consumer through various products such as sandwiches and prepared salads. From farm to fork, the fresh leafy produce supply chain (FLPSC) is complex and contains a diverse range of environments where L. monocytogenes is sporadically detected during routine sampling of produce and processing areas. This review describes sources of the bacteria in the FLPSC and outlines the physiological and molecular mechanisms behind its survival in the different environments associated with growing and processing fresh produce. Finally, current methods of source tracking the bacteria in the context of the food supply chain are discussed with emphasis on how these methods can provide additional, valuable information on the risk that L. monocytogenes isolates pose to the consumer. [ABSTRACT FROM AUTHOR]

Abstract: Aims: The goal of this research is to model the effects of two osmotic solutions factors on the reduction of selected microorganisms, and to assess the application in osmotic dehydration process of animal raw materials from the aspect of microbiological safety. Methods and Results: Sugar beet molasses and aquatic osmotic solution were prepared and inoculated with Escherichia coli, Listeria monocytogenes and Salmonella spp. Varied factors of osmotic solutions were: time, temperature and concentration of osmotic solutions. Samples of osmotic solutions were subjected to standard and modified microbiological ISO methods. The result showed that increase in factors had a positive effect on the reduction of microbiological load, while the time of the process was the most influential technological parameter. Number of L. monocytogenes was reduced to <10 CFU per g at the end of the process in the highest concentration of sugar beet molasses at all process temperatures. Conclusions: Developed mathematical models of reduction ratios for tested microorganisms were statistically significant, allowing good prediction of reduction ratio values based on applied factors. Significance and Impact of the Study: Obtained levels of reduction of all tested microorganisms present good base for the production of safe osmotically dehydrated products of animal origin. [ABSTRACT FROM AUTHOR]

Abstract: Aims: To investigate the effect of gamma radiation and high energy electron beam doses on the inactivation of antibiotic‐susceptible and antibiotic‐resistant Listeria monocytogenes strains inoculated on the surface of raw salmon fillets stored at different temperature (−20, 4 and 25°C). Methods and Results: The population of bacteria strains resistance to penicillin, ampicillin, meropenem, erythromycin and trimethoprim‐sulfamethoxazole was generated. When using gamma irradiation, the theoretical lethal dose ranged from 1·44 to 5·68 kGy and for electron beam the values ranged from 2·99 to 6·83 kGy. The theoretical lethal dose for both radiation methods was higher for antibiotic‐resistant strains. Gamma radiation proved to be a more effective method for extending salmon fillet shelf‐life. The evaluation of pulsed‐field gel electrophoresis electrophoregram revealed that the repair of radiation‐caused DNA damage occurred faster in antibiotic‐resistant L. monocytogenes strains. The number of live L. monocytogenes cells, 40 h after irradiation, also was higher in antibiotic‐resistant strain suspension. Conclusions: The present study showed that gamma radiation was more effective in the elimination of the tested micro‐organisms and food preservation, than a high energy electron beam. The antibiotic‐resistant L. monocytogenes strains were more resistant to both radiation methods. Significance and Impact of the Study: There are a lot of research on the effect of radiation on the number of bacteria in food products. However, there is almost no information about the effect of strain properties, such as drug susceptibility, virulence, etc., on their resistance to ionizing radiation. An increasing number of drug resistant bacterial strains isolated from food, encourages to take up this research subject. [ABSTRACT FROM AUTHOR]

Abstract: Aims: The aims of this study were to characterize the genetic diversity of Listeria monocytogenes isolates obtained from commercial mushroom production, to establish the persistence, recontamination and the risk of cross‐contamination from the working environment to the final products, creating awareness about the presence of L. monocytogenes thus helping to prevent the possibility of cross‐contamination. Methods and Results: From an extensive analysis of commercial mushroom production, analysed with BS EN ISO 11290‐1:1996/Amd 1:2004 and BS EN ISO 11290‐2:1998/Amd 1:2004, 279 L. monocytogenes isolates were obtained. All of the isolates were characterized by pulsed‐field gel electrophoresis, species PCR and serogroup PCR. All the isolates were confirmed as L. monocytogenes; 30·1% were serogroup 1/2b‐3b‐7, 40·8% were serogroup 1/2a‐3a and 29·1% were serogroup 4b‐4d‐4e. There were 77 pulsotypes from the 279 isolates, 40 of the pulsotypes had only one strain and 37 had two or more strains, indicating great diversity in the isolates. Conclusions: The high genetic diversity is indicative of the fact that current hygiene practices are successful at removing L. monocytogenes but that recontamination of the production environment is frequent. Significance and Impact of the Study: The results obtained are very valuable in creating awareness of L. monocytogenes in mushroom production and for the improvement of hygiene practices. [ABSTRACT FROM AUTHOR]

Abstract: Aims: The aim of the study was to evaluate the microbicidal effectiveness of radiant catalytic ionization (RCI) against Listeria monocytogenes strains in the form of planktonic cells and biofilm on food products and food contact surfaces as a method of food preservation. Methods and Results: The study material comprised six strains of L. monocytogenes, isolated from food. Samples of different types of food available by retail (raw carrot, frozen salmon filets, soft cheese) and the fragments of surfaces (stainless steel AISI 304, rubber, milled rock tiles, polypropylene) were used in the experiment. The obtained results showed the effectiveness of RCI in the inactivation of both forms of the tested L. monocytogenes strains on all the surfaces. The effectiveness of RCI for biofilm forms was lower as compared with planktonic forms. The PRR value ranged from 18·19 to 99·97% for planktonic form and from 3·92 to 70·10% for biofilm. Conclusions: The RCI phenomenon induces the inactivation of L. monocytogenes on surfaces of food and materials used in the processing industry to a varying degree, depending on the manner of surface contamination, the properties of the contaminated materials as well as on the origin of the strain and the properties of surrounding dispersive environment in which the micro‐organisms were suspended. Significance and Impact of the Study: Searching of new actions aimed at the reduction of the microbial contamination of food and food contact surfaces are extremely important. RCI method has been already described as an effective technique of microbial and abiotic pollution removal from air. However, our studies provide new, additional data related to evaluation the RCI efficacy against microbes on different surfaces, both in planktonic and biofilm form. [ABSTRACT FROM AUTHOR]

Abstract: Aims: We investigated whether Listeria monocytogenes strains differ in their ability to escape from the primary phagosome after internalization into human intestinal epithelial cells. Methods and Results: Food and clinical strains were used to study specific alleles; the activities of listeriolysin O (LLO) and phospholipases PlcA and PlcB, which promote rupture of the phagocytic vacuole; and initial intracellular bacterial growth in Caco‐2 cells. Results showed no difference in LLO activities between food and clinical strains or among serotypes. In contrast, the LLO truncation mutant lacked detectable haemolytic activity and intracellular growth. PlcA and PlcB produced by the strains of serotypes 4b/4e and 1/2b exhibited significantly lower activities than those of serotypes 1/2a and 1/2c. In contrast, the strains of serotype 1/2b grew significantly faster than those of serotypes 4b/4e and 1/2a. Moreover, the PrfA truncation mutants lacked LLO and phospholipases activities and did not show intracellular growth. Conclusions: We determined that LLO and PrfA mutants exert a significant effect on intracellular growth, although it was unclear from this study whether PlcA and PlcB alleles affect escape from vacuoles. Significance and Impact of the Study: This study estimates that low‐virulence L. monocytogenes strains associated with escape ability from the primary vacuoles are not widely distributed among food strains. [ABSTRACT FROM AUTHOR]

Abstract: Aims: This study aimed to review the microbiological results for raw drinking milk (RDM) samples submitted to Public Health England laboratories between 2014 and 2016 in order to produce up‐to‐date data on the microbiological safety of RDM and inform future risk assessments on its sale. Methods and Results: A total of 902 samples of RDM were collected from retail sale in England for microbiological examination. Overall, 454 of 770 samples (59·0%) taken for routine monitoring were of a satisfactory quality, whilst eight (1·0%) were ‘unsatisfactory and potentially injurious to health’ due to the presence of Shiga toxin‐producing Escherichia coli, Campylobacter or elevated levels of Listeria monocytogenes or coagulase‐positive staphylococci. In contrast, 16 of 114 (14·0%) of samples taken in follow‐up to a previous unsatisfactory result and 5 of 18 (27·8%) of samples related to illness were potentially injurious. A total of 229 of 902 samples (25·4%) gave unsatisfactory results due to elevated aerobic colony counts and/or coliforms, whilst 139 of 902 samples (15·4%) were of borderline quality due to coagulase‐positive staphylococci. Listeria monocytogenes was detected at levels of <100 CFU per ml in 66 of 902 samples (7·3%) and other Listeria species in 44 of 902 samples (4·9%). Conclusions: Pathogens and/or indicators of poor hygiene were present in almost half of samples examined. Cows’ milk samples gave a significantly greater proportion of unsatisfactory results compared to milk from other species (i.e. goat, sheep, buffalo, camel). Significance and Impact of the Study: These results demonstrate the importance of maintaining strict controls on the production and sale of this product. [ABSTRACT FROM AUTHOR]

Abstract: Aims: To select Listeria monocytogenes‐specific single‐chain fragment variable (scFv) antibodies from a phage‐display library by a novel simple and cost‐effective immobilization method. Methods and Results: Light expanded clay aggregate (LECA) was used as biomass support matrix for biopanning of a phage‐display library to select L. monocytogenes‐specific scFv antibody. Four rounds of positive selection against LECA‐immobilized L. monocytogenes and an additional subtractive panning against Listeria innocua were performed. The phage clones selected using this panning scheme and LECA‐based immobilization method exhibited the ability to bind L. monocytogenes without cross‐reactivity toward 10 other non‐L. monocytogenes bacteria. One of the selected phage clones was able to specifically recognize three major pathogenic serotypes (1/2a, 1/2b and 4b) of L. monocytogenes and 11 tested L. monocytogenes strains isolated from foods. Conclusions: The LECA‐based immobilization method is applicable for isolating species‐specific anti‐L. monocytogenes scFv antibodies by phage display. Significance and Impact of the Study: The isolated scFv antibody has potential use in development of immunoassay‐based methods for rapid detection of L. monocytogenes in food and environmental samples. In addition, the LECA immobilization method described here could feasibly be employed to isolate specific monoclonal antibodies against any given species of pathogenic bacteria from phage‐display libraries. [ABSTRACT FROM AUTHOR]

Aims Pathogenic bacteria can spread between individuals or between food items via the surfaces they share. Limiting the survival of pathogens on surfaces, therefore, presents an opportunity to limit at least one route of how pathogens spread. In this study, we propose that a simple coating with the essential oil isoeugenol can be used to circumvent the problem of bacterial transfer via surfaces. Methods and Results Two commonly used materials, stainless steel and polyethylene, were coated by physical adsorption, and the coatings were characterized by Raman spectroscopy, atomic force microscopy and water contact angle measurements. We quantified and visualized the colonization of coated and uncoated surfaces by three bacteria: Staphylococcus aureus, Listeria monocytogenes and Pseudomonas fluorescens. No viable cells were detected on surfaces coated with isoeugenol. Conclusions The isoeugenol coating prepared with simple adsorption proved effective in preventing biofilm formation on stainless steel and polyethylene surfaces. The result was caused by the antibacterial effect of isoeugenol, as the coating did not diminish the adhesive properties of the surface. Significance and Impact of the Study Our study demonstrates that a simple isoeugenol coating can prevent biofilm formation of S. aureus, L. monocytogenes and P. fluorescens on two commonly used surfaces. [ABSTRACT FROM AUTHOR]