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Aims This study aims to investigate the in vitro pathogenicity of Chromobacterium haemolyticum strain WI5 toward the intestinal tract, its resistance to water treatments, and its potential for foodborne transmission through leafy greens produced in hydroponic systems. Methods and results C. haemolyticum WI5 caused cytopathic effects in human colon cells HCT116 and exhibited an 8.2-fold higher cell attachment compared to Salmonella serotype Typhimurium. It showed comparable resistance to sodium hypochlorite (NaOCl) and ultraviolet (UV) treatments as Escherichia coli O157: H7 and Pseudomonas aeruginosa but was more susceptible to desiccation. On lettuce, C. haemolyticum WI5 failed to persist, with counts decreasing below the detection limit (≥4 log reductions) after 3 and 2 days at 4 and 25°C, respectively. Conclusions C. haemolyticum WI5 demonstrated considerable virulence features and high in vitro pathogenicity toward the intestinal tract. NaOCl and UV treatments were effective in disinfecting C. haemolyticum in water. Due to its high susceptibility to desiccation and poor survivability on lettuce, the foodborne transmission potential of C. haemolyticum is considered limited. [ABSTRACT FROM AUTHOR]

Background Salmonella enterica subspecies enterica serovar Saintpaul (S. Saintpaul) is an important gut pathogen which causes salmonellosis worldwide. Although intestinal salmonellosis is usually self-limiting, it can be life-threatening in children, the elderlies and immunocompromised patients. Appropriate antibiotic treatment is therefore required for these patients. However, the efficacy of many antibiotics on S. enterica infections has been greatly compromised due to spreading of multidrug resistance (MDR) plasmids, which poses serious threats on public health and needs to be closely monitored. In this study, we sequenced and fully characterized an S. enterica MDR plasmid pSGB23 isolated from chicken. Results Complete genome sequence analysis revealed that S. Saintpaul strain SGB23 harbored a 254 kb megaplasmid pSGB23, which carries 11 antibiotic resistance genes responsible for resistance to 9 classes of antibiotics and quaternary ammonium compounds that are commonly used to disinfect food processing facilities. Furthermore, we found that pSGB23 carries multiple conjugative systems, which allow it to spread into other Enterobacteriaceae spp. by self-conjugation. It also harbors multiple types of replicons and plasmid maintenance and addictive systems, which explains its broad host range and stable inheritance. Conclusions We report here a novel MDR plasmid pSGB23 harboured by S. enterica. To our knowledge, it carried the greatest number of antibiotic resistance genes with the broadest range of resistance spectrum among S. enterica MDR plasmids identified so far. The isolation of pSGB23 from food sources is worrisome, while surveillance on its further spreading will be carried out based on the findings reported in this study., Author(s): Yichen Ding[sup.1,2,3] , Ye Htut Zwe[sup.4] , Seow Fong Chin[sup.2] , Gurjeet S. Kohli[sup.2] , Daniela I. Drautz-Moses[sup.2] , Michael Givskov[sup.2,5] , Jorgen Schlundt[sup.6] , Stephan C. Schuster[sup.2,3] , [...]

Aims: We investigated the fate of Salmonella in lettuce seeds grown in a hydroponic system and the potentials of applying photodynamic inactivation (PDI) to enhance microbial safety of hydroponic farming systems. Methods and Results: Lettuce was grown from Salmonella‐contaminated seeds, and rose bengal‐mediated PDI was applied. Without intervention, Salmonella could persist in plants and hydroponic farming environment throughout 6 weeks of lettuce growth. Cross‐contamination from Salmonella‐inoculated to noninoculated seedlings was observed. PDI significantly decreased Salmonella from 3.90 ± 0.31 log colony‐forming unit (CFU) per plant to 2.77 ± 0.49 log CFU per plant without extra illumination needed (p < 0.01) by week six. Conclusions: Salmonella from contaminated seeds could survive for an extended period in lettuce and hydroponic farming environment and posed serious cross‐contamination risks. Rose bengal‐mediated PDI showed promise in controlling Salmonella contamination in lettuce in a hydroponic farming setting. Significance and Impact of the Study: This study shed light on the serious food safety implications that Salmonella‐contaminated lettuce seeds might entail in a hydroponic farming environment and demonstrated rose bengal‐mediated PDI as a potential mitigation strategy. These findings contribute to the increasingly relevant field of urban farming systems and their associated food safety concerns. [ABSTRACT FROM AUTHOR]

Although conventionally considered an animal pathogen, recent evidence increasingly suggests that fresh produce may act as significant transmission vehicles and alternative hosts to Salmonella. This study reports the differential survivability of two genetically similar Salmonella Thompson strains (ST 889B and ST 688C) on the adaxial surface of pre-harvest basil (Ocimum basilicum) leaves. Upon inoculation, two distinct phenomena, a dried water-print or a macroscopic lesion, were observed within 24 h. ST 889B survived better than ST 688C on healthy-looking leaves without lesions, possibly due to its higher biofilm-forming ability. Both strains survived better on the leaves with lesions than on the healthy-looking leaves (ST 688C: 4.39 ± 0.68 vs. 2.18 ± 0.29; ST 889B: 4.78 ± 0.12 vs. 2.83 ± 0.18 log CFU per sample at 6 days post-inoculation). ST 889B caused the formation of lesions at a higher frequency [70/117 leaves (59.8%)] than ST 688C [35/96 leaves (36.5%)]. Thus, we highlighted two distinct Salmonella survival strategies in the basil pathosystem and demonstrated gene expression polymorphism (variations in the expression of the same set of genes) as an indispensable strategy in the colonization of plants as hosts by the human pathogens. [ABSTRACT FROM AUTHOR]

Group B Streptococcus (GBS) was previously not known to be transmitted through food, but an outbreak investigation in Singapore in 2015 documented for the first time an association between GBS Type III Sequence Type 283 infection and consumption of raw fish dishes. As very little is known about the survival of GBS during heat treatment and the stomach transit, its survival under simulated conditions was studied, in comparison with that of Escherichia coli O157:H7 and Listeria monocytogenes. The mean D-values of four GBS strains ranging from 0.72 to 0.88 min in neutral pH tryptone soy broth at 56.4 °C and 0.44–1.43 min at pH 2.35 at 37 °C in simulated gastric fluid, were significantly lower (p < 0.05) than those of E. coli O157:H7 and L. monocytogenes. This study suggests possible factors other than acid or heat resistance of GBS to be instrumental to its pathogenicity. [ABSTRACT FROM AUTHOR]

Salmonellosis, caused by multidrug-resistant Salmonella species, in particular, is one of the leading notifiable foodborne diseases in Singapore and an emerging public health concern worldwide. The objectives of this study were to determine the prevalence, antibiotic resistance and the presence of gyrA and parC mutations in Salmonella isolated from retail fresh chicken meat in Singapore. A significantly higher prevalence of Salmonella was found in chicken meat from the wet markets (25%, 30/120), as compared to supermarkets (12.7%, 19/150). The top four serovars isolated in this study were S. Saintpaul (32.7%, 17/52), followed by S. Brancaster (21.2%, 11/52), S. Albany (11.5%, 6/52), and S. Stanley (9.6%, 5/52). More than 80% of Salmonella isolates exhibited resistance to at least one of eleven antibiotics tested. The most common phenotypic resistances exhibited were towards ampicillin (78.8%, 41/52), tetracycline and chloramphenicol (61.5%, 32/52), sulfamethoxazole-trimethoprim (55.8%, 29/52) and nalidixic acid (30.8%, 16/52). Of the 52 Salmonella isolates, 59.6% (31/52) were multi-drug resistant strains, resistant to 3 or more antibiotic classes. No mutation in parC gene was found in any of the isolates that expressed phenotypic resistance or reduced susceptibility towards quinolone and/or fluoroquinolone. Mutations at two different sites of gyrA gene were found in 7 isolates, which further discriminates the quinolone resistance genotype in Salmonella isolates from fresh chicken meat. Our findings provide opportunities for risk assessment and management of salmonellosis and antibiotic-resistant Salmonella species in the country and the region. [ABSTRACT FROM AUTHOR]

Singapore in recent years is dedicating great efforts in developing urban agriculture in production of leafy green vegetables. Considering the small scales and diverse set-ups of local farms, it is necessary to collect baseline data to evaluate the microbial safety of local leafy green production. In this study, we collected lettuce crops and agriculture water used in lettuce production from ten different farms (five soil-based farms and five hydroponic farms, 100 samples over a period of five months) and tested with multiple microbial parameters. As a result, 16 out of the 50 agriculture water samples were enumerated with Escherichia coli (4.15 ± 0.81 log CFU/100 ml from 9 samples collected at soil-based farms, 3.79 ± 0.91 log CFU/100 ml from 7 samples collected at hydroponic farms). For the lettuce crops, 7 out of 25 samples from the soil-based farms (with overhead irrigation) were enumerated with an average of 3.28 ± 1.45 log CFU E. coli /g fresh matter, while all of the 25 samples from the hydroponic farms were below 10 CFU E. coli /g fresh matter. Within the 11 Salmonella strains isolated in this study, six strains were from soil-based agriculture water, four strains were from hydroponic agriculture water, only one strain was isolated from lettuce crops and it was from a hydroponic farm. When tested with lettuce crops grown in the laboratory, the five Salmonella isolates from the hydroponic farms showed a higher likelihood of internalization and translocation from the roots to the aerial parts (6/40 [15%] plants tested positive) than the six Salmonella isolates from the soil-based farms (2/48 [4%] plants tested positive). The opportunistic pathogen Stenotrophomonas maltophilia was detected with higher presence at hydroponic farms than the soil-based farms. Antimicrobial resistance (AMR) analysis were performed over all of the Salmonella and S. maltophilia isolates and no AMR strain has been identified so far. Taken together, these results suggested the great needs of both soil-based and hydroponic farms to improve their good agriculture practices such as to implement effective agriculture water treatment and to avoid using overhead irrigation with sprinkler systems. [ABSTRACT FROM AUTHOR]

Due to rapidly falling costs, whole genome sequencing (WGS) is becoming an essential tool in the surveillance of antimicrobial resistance (AMR) in Salmonella enterica. Although there have been many recent works evaluating the accuracy of WGS in predicting AMR from a large number of Salmonella isolates, little attention has been devoted to deciphering the underlying causes of disagreement between the WGS genotype and experimentally determined AMR phenotype. This study analyzed the genomes of six S. enterica isolates previously obtained from raw chicken which exhibited disagreements between WGS genotype and AMR phenotype. A total of five WGS false negative predictions toward ampicillin, amoxicillin/clavulanate, colistin, and fosfomycin resistance were presented in conjunction with their corresponding empirical phenotypic and/or genetic evidence of heteroresistance. A further case study highlighting the inherent limitations of WGS to detect the underlying genetic mechanisms of colistin heteroresistance was presented. These findings implicate heteroresistance as an underlying cause for false negative WGS-based AMR predictions in S. enterica and suggest that widespread use of WGS in the surveillance of AMR in food isolates might severely underestimate true resistance rates. • Unstable, temporary changes in genetic elements cause heteroresistance. • Resistance due to heteroresistance cannot be detected by whole genome sequencing. • Resistance to last-line drug colistin was detected from foodborne Salmonella. • Widespread use of WGS may under-estimate true resistance rate. [ABSTRACT FROM AUTHOR]

Background: Salmonella enterica subspecies enterica serovar Saintpaul (S. Saintpaul) is an important gut pathogen which causes salmonellosis worldwide. Although intestinal salmonellosis is usually self-limiting, it can be life-threatening in children, the elderlies and immunocompromised patients. Appropriate antibiotic treatment is therefore required for these patients. However, the efficacy of many antibiotics on S. enterica infections has been greatly compromised due to spreading of multidrug resistance (MDR) plasmids, which poses serious threats on public health and needs to be closely monitored. In this study, we sequenced and fully characterized an S. enterica MDR plasmid pSGB23 isolated from chicken. Results: Complete genome sequence analysis revealed that S. Saintpaul strain SGB23 harbored a 254 kb megaplasmid pSGB23, which carries 11 antibiotic resistance genes responsible for resistance to 9 classes of antibiotics and quaternary ammonium compounds that are commonly used to disinfect food processing facilities. Furthermore, we found that pSGB23 carries multiple conjugative systems, which allow it to spread into other Enterobacteriaceae spp. by self-conjugation. It also harbors multiple types of replicons and plasmid maintenance and addictive systems, which explains its broad host range and stable inheritance. Conclusions: We report here a novel MDR plasmid pSGB23 harboured by S. enterica. To our knowledge, it carried the greatest number of antibiotic resistance genes with the broadest range of resistance spectrum among S. enterica MDR plasmids identified so far. The isolation of pSGB23 from food sources is worrisome, while surveillance on its further spreading will be carried out based on the findings reported in this study. [ABSTRACT FROM AUTHOR]

A 405 ± 5-nm LED illumination was evaluated for its antibacterial effect against Salmonella Enteritidis in phosphate buffered saline (PBS) and on the surface of cooked chicken. Its antibacterial mechanism was also elucidated by determining the injury of cellular components using metabolic inhibitors. LED illuminated three S . Enteritidis strains in PBS at doses as high as 0.45 kJ/cm 2 (for 7.5 h) and on cooked chicken at doses of 1.58–3.80 kJ/cm 2 (for 20–48 h) at 4, 10, and 20 °C. Results showed that illumination inactivated 1.4–2.1 log CFU/ml of populations in PBS at 0.45 kJ/cm 2 , indicating that S . Enteritidis 130 was more susceptible to illumination than 124 and 125 strains. At 4 °C, Salmonella populations on illuminated cooked chicken decreased by 0.8–0.9 log CFU/cm 2 at 3.80 kJ/cm 2 , whereas bacterial growth inhibition and delay were observed by illumination at 10 and 20 °C, respectively, regardless of bacterial strain. These results indicate that illumination temperature significantly ( P ≤ 0.05) influenced the antibacterial effect of LED on cooked chicken. LED illumination at 4 °C resulted in the incapability of Salmonella cells to repair cellular damage related to metabolism of DNA, RNA, protein, and cell wall. These results suggest that 405 ± 5-nm LEDs under refrigeration conditions could control Salmonella linked to cooked chicken. [ABSTRACT FROM AUTHOR]

Fermentation, especially spontaneous fermentation, has become from an ancient food preservation method to a stylish cooking trend in very recent years. Accordingly, the associated food safety should be revisited, particularly since inexperienced people increasingly performing spontaneous fermentation on an ad hoc basis. In this study, three lactic acid bacteria (LAB) strains were tested. Lactiplantibacillus plantarum 299v at high initial inoculation levels (>6 log CFU/mL brine water) effectively eliminated Salmonella spiked in a carrot fermentation system from 4.6 ± 0.2 log CFU/mL to < 1 log CFU/mL after 7 days fermentation at 20 °C. Next, the bacterial enumeration and 16s rRNA gene sequencing results between spontaneous fermentation and fermentation samples using L. plantarum 299v as the starter culture were compared. It was found that the inhibiting effect of L. plantarum 299v could be extended beyond Salmonella spp. to the entire Enterobacteriaceae family during the carrot fermentation. Therefore, our study suggests that in comparison with spontaneous fermentation, selected starter culture such as L. plantarum 299v can consistently improve the safety and quality of fermented foods. • Spontaneous fermentation was compared with fermentation using starter culture. • L. plantarum 299 V as starter culture suppresses Enterobacteriaceae. • L. plantarum 299 V improves the safety and quality of fermented foods. • Probiotics as starter culture increases the health benefits of fermented products. [ABSTRACT FROM AUTHOR]