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The foodborne pathogen Listeria monocytogenes can persist in produce processing environments, which increases the risk for food contamination. Increased resistance to antimicrobials commonly used in cleaning and sanitizing procedures may contribute to L. monocytogenes’ persistence in these environments. This study aimed to evaluate sanitizer resistance in L. monocytogenes isolates collected from three tree fruit packing facilities (F1, F2, and F3) during packing seasons 2020–2021 (Y1) and 2021–2022 (Y2), and to assess evidence of persistence based on the genomic similarity of isolates to historical isolates collected in previous years. L. monocytogenes isolates collected in 2020–2022 (n = 44) were tested for resistance to peroxyacetic acid (PAA) and a proprietary biofilm−removing agent using a broth microdilution assay. Further, L. monocytogenes isolates were whole genome sequenced and screened for the presence of antimicrobial resistance and virulence genes, as well as to assess the genomic similarity of isolates using the CFSAN SNP bioinformatic pipeline. Over half (57%) of the tested isolates had a PAA minimum inhibitory concentration (MIC) of 250 ppm, which was similar to the applied concentration of the PAA sanitizer in the three facilities (230 ppm). In contrast, 80% of tested isolates had a biofilm remover MIC of 0.13 ppm, which was substantially below the concentration applied in the facilities (137 ppm). Genomes of all tested isolates carried antimicrobial resistance (fosX, lin, mdrL, mprF, and norB) and virulence (inlA, inlB, plcA, plcB, prfA, hly, mpl, and iap) genes. L. monocytogenes isolates collected between 2020 and 2022 belonged to three distinct lineages, with 22 multilocus sequence types (MLSTs) belonging to 22 different clonal complexes. Genomic similarity analysis with historical isolates collected from the same facilities in 2016–2017 demonstrated a 5-year persistence of the genotypes ST 1003 and ST 554 in F2, which were no longer detected in 2022. Overall, our results highlight the need to re-evaluate sanitizer concentrations to effectively control persistent L. monocytogenes strains in tree fruit packing facilities.

Food-contact surfaces showing signs of wear pose a substantial risk of Listeria monocytogenes contamination and may serve as persistent sources of cross-contamination in fresh produce packinghouses. This study offers a comprehensive exploration into the influence of surface defects on the efficacies of commonly used sanitizers against L. monocytogenes biofilms on major food-contact surfaces. The 7-day-old L. monocytogenes biofilms were cultivated on food-contact surfaces, including stainless steel, polyvinyl chloride, polyester, low-density polyethylene, and rubber, with and without defects and organic matter. Biofilms on those surfaces were subjected to treatments of 200 ppm chlorine, 400 ppm quaternary ammonium compound (QAC), or 160 ppm peroxyacetic acid (PAA). Results showed that surface defects significantly (P

Our previous survey revealed the poor microbial quality of leafy green vegetables and the presence of Salmonella on these vegetables grown and sold in Accra, Ghana. This study validated the efficacy of some cleaning and sanitation methods (tap water, salt solution, lemon juice, and vinegar) commonly used by Ghanaian households, by comparing them with the performance of several sanitation approaches used by the U.S. fresh produce industry (chlorine, peracetic acid, and ozonated water) in reducing Salmonella populations on leafy green vegetables. Cabbage and lettuce leaves inoculated with each of three Salmonella cocktails were treated with sterile water and the previously mentioned six sanitizers. The efficacies of the treatments were evaluated by using the standard plate count assay. The effect of the treatments on the sensory quality of treated vegetables was evaluated by a 97-member consumer panel in the United States. Treatments with citric and acetic acid were as effective as chlorine and peracetic acid in reducing Salmonella counts on vegetable leaves. Ozonated water was less effective than the two organic acids but equally as effective as treatment with the salt solution. Rinsing vegetables with water did not significantly reduce Salmonella counts (P > 0.05). Cabbage leaves treated with citric acid, vinegar, and water were more preferred (P ≤ 0.05) by the consumer panel, while chlorine-treated cabbage leaves were the least preferred. Lettuce samples treated with citric acid and water were more preferred, and salt-treated samples were least preferred. Among the vegetable sanitation methods used by Ghanaian households, treatments with citric and acetic acid are effective in inactivating Salmonella without adversely affecting the sensory quality of treated vegetables. [ABSTRACT FROM AUTHOR]

The foodborne pathogen Listeria monocytogenes can persist in produce processing environments, which increases the risk for food contamination. Increased resistance to antimicrobials commonly used in cleaning and sanitizing procedures may contribute to L. monocytogenes' persistence in these environments. This study aimed to evaluate sanitizer resistance in L. monocytogenes isolates collected from three tree fruit packing facilities (F1, F2, and F3) during packing seasons 2020-2021 (Y1) and 2021-2022 (Y2), and to assess evidence of persistence based on the genomic similarity of isolates to historical isolates collected in previous years. L. monocytogenes isolates collected in 2020-2022 (n = 44) were tested for resistance to peroxyacetic acid (PAA) and a proprietary biofilm-removing agent using a broth microdilution assay. Further, L. monocytogenes isolates were whole genome sequenced and screened for the presence of antimicrobial resistance and virulence genes, as well as to assess the genomic similarity of isolates using the CFSAN SNP bioinformatic pipeline. Over half (57%) of the tested isolates had a PAA minimum inhibitory concentration (MIC) of 250 ppm, which was similar to the applied concentration of the PAA sanitizer in the three facilities (230 ppm). In contrast, 80% of tested isolates had a biofilm remover MIC of 0.13 ppm, which was substantially below the concentration applied in the facilities (137 ppm). Genomes of all tested isolates carried antimicrobial resistance (fosX, lin, mdrL, mprF, and norB) and virulence (inlA, inlB, plcA, plcB, prfA, hly, mpl, and iap) genes. L. monocytogenes isolates collected between 2020 and 2022 belonged to three distinct lineages, with 22 multilocus sequence types (MLSTs) belonging to 22 different clonal complexes. Genomic similarity analysis with historical isolates collected from the same facilities in 2016-2017 demonstrated a 5-year persistence of the genotypes ST 1003 and ST 554 in F2, which were no longer detected in 2022. Overall, our results highlight the need to re-evaluate sanitizer concentrations to effectively control persistent L. monocytogenes strains in tree fruit packing facilities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Agricultural water is a known source of contamination to fresh produce and can contain foodborne pathogens including Salmonella enterica, pathogenic Escherichia coli, Listeria monocytogenes, and Campylobacter jejuni. To mitigate such risks, antimicrobial agents such as hypochlorites and peroxyacetic acid (PAA) can be applied to in-line irrigation systems as well as to water used in postharvest washing. Although these compounds are effective and widely used, some pathogenic bacteria adapt to survive exposure. RNA sequencing was used to analyze the Salmonella Newport transcriptome after exposure to sodium hypochlorite (NaOCl) and PAA in a simulated agricultural water system. Overall cellular adaptive response was determined quantitatively as a function of overall gene expression of the >4,000 genes in the Salmonella Newport genome. Differentially expressed genes ranged from 11 due to 10-ppm NaOCl treatment, 316 due to 20-ppm NaOCl treatment, 1,719 due to 10-ppm PAA treatment, and 2,010 due to 20-ppm PAA treatment compared with that of the controls (water only). Differentially expressed transcripts included cellular functions such as biosynthesis, degradation, energy generation, and nonmetabolically linked functions. Oxidative exposure upregulated genes associated with key virulence, attachment, and gene transfer. Amino acid biosynthesis was upregulated due to NaOCl exposure but primarily downregulated when Salmonella Newport was exposed to PAA. Slight upregulation occurred in nucleoside and nucleotide biosynthesis, a known DNA repair mechanism seen during exposure to sanitizers. Our results indicate that Salmonella Newport reacts differently when exposed to NaOCl versus PAA, despite oxidative activity being the primary modes of antimicrobial action of both compounds. [ABSTRACT FROM AUTHOR]

Food-contact surfaces showing signs of wear pose a substantial risk of Listeria monocytogenes contamination and may serve as persistent sources of cross-contamination in fresh produce packinghouses. This study offers a comprehensive exploration into the influence of surface defects on the efficacies of commonly used sanitizers against L. monocytogenes biofilms on major food-contact surfaces. The 7-day-old L. monocytogenes biofilms were cultivated on food-contact surfaces, including stainless steel, polyvinyl chloride, polyester, low-density polyethylene, and rubber, with and without defects and organic matter. Biofilms on those surfaces were subjected to treatments of 200 ppm chlorine, 400 ppm quaternary ammonium compound (QAC), or 160 ppm peroxyacetic acid (PAA). Results showed that surface defects significantly (P < 0.05) increased the population of L. monocytogenes in biofilms on non-stainless steel surfaces and compromised the efficacies of sanitizers against L. monocytogenes biofilms across various surface types. A 5-min treatment of 200 ppm chlorine caused 1.84-3.39 log 10  CFU/coupon reductions of L. monocytogenes on worn surfaces, compared to 2.79-3.93 log 10  CFU/coupon reduction observed on new surfaces. Similarly, a 5-min treatment with 400 ppm QAC caused 2.05-2.88 log 10  CFU/coupon reductions on worn surfaces, compared to 2.51-3.66 log 10  CFU/coupon reductions on new surfaces. Interestingly, PAA sanitization (160 ppm, 1 min) exhibited less susceptibility to surface defects, leading to 3.41-4.35 log 10  CFU/coupon reductions on worn surfaces, in contrast to 3.68-4.64 log 10  CFU/coupon reductions on new surfaces. Furthermore, apple juice soiling diminished the efficacy of sanitizers against L. monocytogenes biofilms on worn surfaces (P < 0.05). These findings underscore the critical importance of diligent equipment maintenance and thorough cleaning processes to effectively eliminate L. monocytogenes contamination on food-contact surfaces., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Listeria species are ubiquitous in nature and can adapt to survive in a variety of niches, including food processing environments. Listeria species that colonize these environments may also have the potential to persist. Food safety strategies designed to manage these niches include regular cleaning and disinfection with proven sanitizers containing biocide-active compounds. Typically, these sanitizers are effective against bacteria growing under planktonic conditions, but their efficacy may be compromised when bacteria are contained in biofilms. The susceptibility of persistent Listeria isolates, i.e., those capable of forming biofilms, to a selection of sanitizers was investigated. A quaternary ammonium compound-based sanitizer was the biocide most effective against planktonic bacteria, with a MIC of 0.0015 to 0.006%. In contrast, ethanol-based sanitizers were the least effective. Although, no triclosan tolerance was observed for planktonic Listeria isolates, triclosan was the only biocide that resulted in a significant biomass reduction. Differences between Listeria species were observed; L. monocytogenes and L. welshimeri biofilms were more tolerant to quaternary ammonium compound-based sanitizers than were L. innocua biofilms. These findings extend our understanding of the application of commonly used sanitizers in the food industry and the efficacy of these sanitizers against Listeria species and their associated biofilms. [ABSTRACT FROM AUTHOR]

Although frozen dairy desserts have a strong record of safety, recent outbreaks of foodborne disease linked to ice creams have brought new attention to this industry. There is concern that small-scale frozen dessert equipment may not comply with or be reviewed against published comprehensive design and construction sanitation specifications (National Sanitation Foundation or 3-A sanitary standards). Equipment sanitary design issues may result in reduced efficacy of cleaning and sanitation, thus increasing the likelihood of postprocess contamination with pathogenic bacteria. In this context, and given that Listeria monocytogenes outbreaks are of great concern for the frozen dessert industry, a complementary study was conducted to evaluate the fate of L. monocytogenes in ice cream mix on a stainless steel surface. Our results showed that L. monocytogenes survived for up to 6 weeks at room temperature and 9 weeks at 4°C in contaminated ice cream on a stainless steel surface. Furthermore, chlorine- and acid-based surface sanitizers had no detrimental effect on the L. monocytogenes when used at a concentration and contact time (1 min) recommended by the manufacturer; significant reduction in CFU required 5 to 20 min of contact time. [ABSTRACT FROM AUTHOR]

Techniques for measuring ATP bioluminescence are being used widely as rapid methods for the assessment of the cleanliness of food-processing plants. Sanitizer or cleanser residues could present a potential problem in the use of these ATP bioluminescence techniques due to the degradation of the firefly luciferin-luciferase substrate-enzyme system by these cleaning chemicals. The objectives of this study were the evaluation of the quenching and enhancement effects on the detection of the ATP bioluminescence signal using various ATP extractants, commercial cleansers, and sanitizers, and the determination of the antimicrobial properties of different concentrations of cleansers and sanitizers on Escherichia coli OI57:H7, Listeria monocytogenes , Staphylococcus aureus , and Pseudomonasfragi . Extractants evaluated were benzalkonium chloride, Triton X-100,benzethonium chloride, cetylpyridinium chloride, and trichloroacetic acid. Cleansers evaluated were an alkaline foam and an acid foam. Also evaluated were a quaternary ammonium sanitizer, a d-limolene sanitizer, commercial sodium hypochlorite, and household bleach (sodium hypochlorite). The extractant cetylpyridinium chloride (0.0125%) did not have a statistically significant effect on the detection of the ATP bioluminescence signal at a 95% confidence level. A transition from enhancement to quenching as a concentration-dependent phenomenon was observed for the alkaline foam, acid foam, commercial sodiumhypochlorite,d-limolene,and household bleach. An enhancement effect that did not appear to be concentration-dependent was observed for the quaternary ammonium sanitizer. Antimicrobial disc assays demonstrated that in some cases the cleanser or sanitizer concentration was not effective against the bacteria, but enhanced or quenched the detection of the bioluminescence signal, leading to false-positive or false-negative results respectively.

We tested the hypothesis that exposure of Listeria monocytogenes to sublethal levels of sanitizers (chemical shock) could affect survival to a subsequent exposure to lethal levels and the ability of the cells to attach to stainless steel surfaces. L. monocytogenes was exposed to an acidic anionic sanitizer, a chlorine-based sanitizer, an iodophor, and a quaternary ammonium compound, as well as to citric, lactic, and propionic acids. The cells were exposed to sublethal levels of each sanitizer for up to 60 min (chemical shock), followed by exposure to either the minimum inhibitory concentration (MIC) for 48 h, to the lethal level for 48 h, or to the MIC for 40 min followed by the lethal level for 48 h. No significant difference in survival was observed with most of the sanitizers used. However, exposure to a chemical shock with the acid anionic sanitizer for at least 10 min resulted in survival of the cells in the MIC of this sanitizer, as well as in the lethal level, but only when the cells were first exposed to the MIC for 40 min. Deliberate dissociation of citric acid by pH adjustment also resulted in survival of chemically shocked cells to lethal levels of this acid, suggesting that exposure to the dissociated form somehow enabled cells to survive exposure to lethal levels of the acid. Chemical shock did not affect attachment of the cells to stainless-steel chips.