Identification of Listeria monocytogenes Contamination in a Ready-to-Eat Meat Processing Plant in China

Recent advances in examining the factors influencing the efficacy of biocides against Listeria monocytogenes biofilms in the food industry: A systematic review

Controlling Listeria monocytogenes and its associated biofilms in the food industry requires various disinfection techniques, including physical, chemical, and biological treatments. Biocides, owing to their ease of use, cost-effectiveness, dissolvability in water, and efficacy against a wide range of microorganisms, are frequently selected options. Nonetheless, concerns have been raised about their efficacy in controlling L. monocytogenes biofilm, as laboratory-based and commercial studies have reported the persistence of this bacterium after cleaning and disinfection. This review systematically examined scientific studies, sourced from the Web of Science, Scopus, and PubMed databases between January 2010 and May 2024, that investigated the effectiveness of the most commonly used biocides in the food industry against L. monocytogenes biofilms. A total of 92 articles which met the screening criteria, were included, with studies utilizing biocides containing sodium hypochlorite, quaternary ammonium compounds, and peroxyacetic acid being predominant. Studies indicated that several key factors may potentially influence biocides' efficacy against L. monocytogenes biofilms. These factors included strain type (persistent, sporadic), serotype, strain origin (clinical, environmental, or food), surface type (biotic or abiotic), surface material (stainless steel, polystyrene, etc.), incubation time (biofilm age) and temperature, presence of organic matter, biocide's active agent, and the co-culture of L. monocytogenes with other bacteria. The induction of the viable but nonculturable (VBNC) state following disinfection is also a critical concern. This review aims to provide a global understanding of how L. monocytogenes biofilms respond to biocides under different treatment conditions, facilitating the development of effective cleaning and disinfection strategies in the food industry.

Occurrence, Molecular Serogroups, Antimicrobial Susceptibility and Identification by MALDI-TOF MS of Listeria monocytogenes Isolated from RTE Meat Products in Southern Poland

L. monocytogenes is considered one of the most dangerous foodborne pathogens. This study aimed to determine the occurrence of L. monocytogenes in RTE meat products from southern Poland, including serogroups and antimicrobial susceptibility, and to assess the usefulness of MALDI-TOF MS as a tool for identifying L. monocytogenes. A total of 848 production batches of RTE meat products were analyzed for L. monocytogenes. All L. monocytogenes isolates were serotyped using the multiplex PCR method, tested for antimicrobial susceptibility using the disk diffusion method and identified using the MALDI-TOF MS method. L. monocytogenes was detected in 52/848 batches of RTE meat products (6.13%). The isolates belonged to four serogroups: 17/52 (33%) isolates to IVb; 15/52 (29%) isolates to IIa; 10/52 (19%) isolates to IIc and 10/52 (19%) isolates to IIb. All isolates (52/52) showed susceptibility to the tested antimicrobials. Using MALDI-TOF MS, 10/52 isolates (19.2%) were identified at the level of secure genus identification, probable species identification; 37/52 isolates (71.2%) were identified at the level of probable genus identification; 3/52 isolates (5.8%) were incorrectly identified as L. innocua; and 2/52 isolates (3.8%) were not identified. The occurrence of L. monocytogenes in RTE meat products was low. Almost half of the analyzed isolates were L. monocytogenes of serogroups, which are most often associated with listeriosis in humans in Poland. All isolates showed susceptibility to five commonly used antimicrobials for treating listeriosis. The use of MALDI-TOF MS as a tool for the identification of L. monocytogenes indicated its limitations related to the insufficient representation of the pathogen in the reference database.

Comprehensive Review on the Biocontrol of Listeria monocytogenes in Food Products

Listeria monocytogenes is a foodborne pathogen that causes listeriosis, a group of human illnesses that appear more frequently in countries with better-developed food supply systems. This review discusses the efficacy of actual biocontrol methods combined with the main types of food involved in illnesses. Comments on bacteriophages, lactic acid bacteria, bacteriocins, essential oils, and endolysins and derivatives, as main biological antilisterial agents, are made bearing in mind that, using them, food processors can intervene to protect consumers. Both commercially available antilisterial products and solutions presented in scientific papers for mitigating the risk of contamination are emphasized. Potential combinations between different types of antilisterial agents are highlighted for their synergic effects (bacteriocins and essential oils, phages and bacteriocins, lactic acid bacteria with natural or synthetic preservatives, etc.). The possibility to use various antilisterial biological agents in active packaging is also presented to reveal the diversity of means that food processors may adopt to assure the safety of their products. Integrating biocontrol solutions into food processing practices can proactively prevent outbreaks and reduce the occurrences of L. monocytogenes-related illnesses.

Prevalence of Listeria monocytogenes in RTE Meat Products of Quevedo (Ecuador)

Listeria monocytogenes is a foodborne pathogen that causes listeriosis and can be a problem in areas where meat products are sold at unregulated storage temperatures. In this work, the prevalence of L. monocytogenes was determined in the five most widely traded meat products in the province of Quevedo (Ecuador): bacon, "chorizo paisa", grilled hamburger meat, mortadella, and salami. A total of 1000 samples of these products were analyzed in two seasons of the year (dry season/rainy season). All L. monocytogenes isolates were confirmed by PCR with primers designed for the iap gene. Furthermore, the positive samples were quantified for L. monocytogenes. Of the 1000 meat products analyzed, 163 were positive for L. monocytogenes (16.3%). The prevalence of L. monocytogenes in the two seasons in different meat products was as follows: 22.5% in mortadella, 19% in hamburger meat, 15% in bacon, 14.5% in chorizo paisa and 10.5% in salami. In addition, the concentration of L. monocytogenes in most of the positive samples was in the range of 4-6 log CFU/g or even higher. The results show the need for improvements in the hygienic measures and meat storage temperatures in Quevedo (Ecuador) to avoid risks of foodborne listeriosis.

One Health: a holistic approach for food safety in livestock

The food safety of livestock is a critical issue between animals and humans due to their complex interactions. Pathogens have the potential to spread at every stage of the animal food handling process, including breeding, processing, packaging, storage, transportation, marketing and consumption. In addition, application of the antibiotic usage in domestic animals is a controversial issue because, while they can combat food-borne zoonotic pathogens and promote animal growth and productivity, they can also lead to the transmission of antibiotic-resistant microorganisms and antibiotic-resistant genes across species and habitats. Coevolution of microbiomes may occur in humans and animals as well which may alter the structure of the human microbiome through animal food consumption. One Health is a holistic approach to systematically understand the complex relationships among humans, animals and environments which may provide effective countermeasures to solve food safety problems aforementioned. This paper depicts the main pathogen spectrum of livestock and animal products, summarizes the flow of antibiotic-resistant bacteria and genes between humans and livestock along the food-chain production, and the correlation of their microbiome is reviewed as well to advocate for deeper interdisciplinary communication and collaboration among researchers in medicine, epidemiology, veterinary medicine and ecology to promote One Health approaches to address the global food safety challenges.

Persistence of Listeria monocytogenes ST5 in Ready-to-Eat Food Processing Environment

Most human listeriosis is foodborne, and ready-to-eat (RET) foods contaminated by Listeria monocytogenes during processing are found to be common vehicles. In this study, a total of four L. monocytogens STs (ST5, ST121, ST120, and ST2) have been identified in two RTE food plants from 2019 to 2020 in Shanghai, China. The L. monocytogenes ST5 was predominant in one RTE food processing plant, and it persists in the RTE meat processing plant with continued clone transmission. The genetic features of the four STs isolates were different. ST5 and ST121 had the three genes clpL, mdrL, and lde; however, ST120 and ST2 had two genes except for clpL. SSI-1was present in ST5, ST121, and ST120. Additionally, SSI-2 was present only in the ST121 isolates. ST120 had all six biofilm-forming associated genes (actA, prfA, lmo0673, recO, lmo2504 and luxS). The ST2 isolate had only three biofilm-forming associated genes, which were prfA, lmo0673, and recO. The four ST isolates had different biofilm formation abilities at different stages. The biofilm formation ability of ST120 was significantly higher when grown for one day. However, the biofilm formation ability of ST120 reduced significantly after growing for four days. In contrast, the biofilm formation ability of ST5 and ST121 increased significantly. These results suggested that ST5 and ST121 had stronger ability to adapt to stressful environments. Biofilms formed by all four STs grown over four days can be sanitized entirely by a disinfectant concentration of 500 mg/L. Additionally, only ST5 and ST121 biofilm cells survived in sub-lethal concentrations of chlorine-containing disinfectant. These results suggested that ST5 and ST121 were more resistant to chlorine-containing disinfectants. These results indicated that the biofilm formation ability of L. monocytogenes isolates changed at different stages. Additionally, the persistence in food processing environments might be verified by the biofilm formation, stress resistance, etc. Alternatively, these results underlined that disinfectants should be used at lethal concentrations. More attention should be paid to ST5 and ST121, and stronger surveillance should be taken to prevent and control the clonal spread of L. monocytogenes isolates in food processing plants in Shanghai.

Genetic diversity of Listeria monocytogenes isolates from farm products in Shanghai, China

Farm products are considered important vehicles for the transmission of Listeria monocytogenes. The typing of L. monocytogenes from farm products contributes to the surveillance and source tracing of the pathogen. In this study, 77 L. monocytogenes strains from seven farm product categories in Shanghai were analyzed by serological typing, multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and whole-genome nucleotide polymorphism (wgSNP). The results showed that the 77 isolates were classified into four serovars (1/2a, 1/2c, 1/2b and 4b), and of these, 1/2a (n=47) was the most prevalent. Seventeen sequence types (STs) were generated by MLST with two novel STs (ST1402 and ST1403), and 20 of 77 L. monocytogenes isolates had high genetic identity with previously documented outbreak isolates according to the minimum spanning tree from the MLST results. Moreover, 34 PFGE patterns (PF1-PF34) were differentiated, and based on a similarity value higher than 80% by the UPGMA dendrogram, the discriminatory index was relatively low (equal to 0.775). Furthermore, 14 isolates were chosen and further analyzed by wgSNP based on the previous typing results, which demonstrated that wgSNP and MLST yielded mostly consistent typing results but higher resolution than PFGE. In conclusion, 77 L. monocytogenes isolates from farm products collected in nine districts in Shanghai were highly genetically diverse, and 20 of these isolates had high relatedness with previously documented outbreak strains worldwide. The results indicate a possible cross-contamination risk of L. monocytogenes and a potential public health concern resulting from farm products during the supply chain in Shanghai, China.

Frozen Vegetable Processing Plants Can Harbour Diverse Listeria monocytogenes Populations: Identification of Critical Operations by WGS

Frozen vegetables have emerged as a concern due to their association with foodborne outbreaks such as the multi-country outbreak of Listeria monocytogenes serogroup IVb linked to frozen corn. The capacity of L. monocytogenes to colonize food-processing environments is well-known, making the bacteria a real problem for consumers. However, the significance of the processing environment in the contamination of frozen foods is not well established. This study aimed to identify potential contamination niches of L. monocytogenes in a frozen processing plant and characterize the recovered isolates. A frozen vegetable processing plant was monitored before cleaning activities. A total of 78 points were sampled, including frozen vegetables. Environmental samples belonged to food-contact surfaces (FCS); and non-food-contact surfaces (n-FCS). Positive L. monocytogenes samples were found in FCS (n = 4), n-FCS (n = 9), and the final product (n = 1). A whole-genome sequencing (WGS) analysis revealed two clusters belonging to serotypes 1/2a-3a and 1/2b-3b). The genetic characterization revealed the presence of four different sequence types previously detected in the food industry. The isolate obtained from the final product was the same as one isolate found in n-FCS. A multi-virulence-locus sequence typing (MVLST) analysis showed four different virulence types (VT). The results obtained highlight the relevant role that n-FCS such as floors and drains can play in spreading L. monocytogenes contamination to the final product.

Molecular subtyping for source tracking of Escherichia coli using core genome multilocus sequence typing at a food manufacturing plant

When harmful bacteria are detected in the final product at a food manufacturing plant, it is necessary to identify and eliminate the source of contamination so that it does not occur again. In the current study, the source of contamination was tracked using core genome multilocus sequence typing (cgMLST) analysis in cases where Escherichia coli was detected in the final product at a food manufacturing plant. cgMLST analysis was performed on 40 strains of E. coli collected from the environment [floor (26 strains), drainage ditch (5 strains), container (4 strains), post-heating production line (1 strain)] and products [final product (3 strains) and intermediate product (1 strain)]. In total, 40 E. coli isolates were classified into 17 genogroups by cgMLST analysis. The 4 E. coli strains isolated from the intermediate and final products were classified into two genogroups (I and II). Certain isolates collected from the environment also belonged to those genogroups, it was possible to estimate the transmission of E. coli in the manufacturing plant. Thus, the dynamics of E. coli in the food manufacturing location were clarified by using cgMLST analysis. In conclusion, our results indicate that cgMLST analysis can be effectively used for hygiene management at food manufacturing locations.

Harnessing Whole Genome Sequence Data for Facility-Specific Signatures for Listeria monocytogenes: A Case Study With Turkey Processing Plants in the United States

Listeria monocytogenes is a Gram-positive foodborne pathogen responsible for the severe disease listeriosis and notorious for its ability to persist in food processing plants, leading to contamination of processed, ready-to-eat foods. L. monocytogenes persistence in various food processing environments (FPEs) has been extensively investigated by various subtyping tools, with increasing use of whole genome sequencing (WGS). However, major knowledge gaps remain. There is a need for facility-specific molecular signatures not only for adequate attribution of L. monocytogenes to a specific FPE but also for improved understanding of the ecology and evolution of L. monocytogenes in the food processing ecosystem. Furthermore, multiple strains can be recovered from a single FPE sample, but their diversity can be underestimated with common molecular subtyping tools. In this study we investigated a panel of 54 L. monocytogenes strains from four turkey processing plants in the United States. A combination of WGS and phenotypic assays was employed to assess strain persistence as well as identify facility-specific molecular signatures. Comparative analysis of allelic variation across the whole genome revealed that allelic profiles have the potential to be specific to individual processing plants. Certain allelic profiles remained associated with individual plants even when closely-related strains from other sources were included in the analysis. Furthermore, for certain sequence types (STs) based on the seven-locus multilocus sequence typing scheme, presence and location of premature stop codons in inlA, inlB length, prophage sequences, and the sequence content of a genomic hotspot could serve as plant-specific signatures. Interestingly, the analysis of different isolates from the same environmental sample revealed major differences not only in serotype and ST, but even in the sequence content of strains of the same ST. This study highlights the potential for WGS data to be deployed for identification of facility-specific signatures, thus facilitating the tracking of strain movement through the food chain. Furthermore, deployment of WGS for intra-sample strain analysis allows for a more complete environmental surveillance of L. monocytogenes in food processing facilities, reducing the risk of failing to detect strains that may be clinically relevant and potentially novel.

Antibacterial Activity of Pediocin and Pediocin-Producing Bacteria Against Listeria monocytogenes in Meat Products

One of the most important challenges in the food industry is to produce healthy and safe food products, and this could be achieved through various processes as well as the use of different additives, especially chemical preservatives. However, consumer awareness and concern about chemical preservatives have led researchers to focus on the use of natural antimicrobial compounds such as bacteriocins. Pediocins, which belong to subclass IIa of bacteriocin characterized as small unmodified peptides with a low molecular weight (2.7-17 kDa), are produced by some of the Pediococcus bacteria. Pediocin and pediocin-like bacteriocins exert a broad spectrum of antimicrobial activity against Gram-positive bacteria, especially against pathogenic bacteria, such as Listeria monocytogenes through formation of pores in the cytoplasmic membrane and cell membrane dysfunction. Pediocins are sensitive to most protease enzymes such as papain, pepsin, and trypsin; however, they keep their antimicrobial activity during heat treatment, at low temperatures even at -80°C, and after treatment with lipase, lysozyme, phospholipase C, DNase, or RNase. Due to the anti-listeria activity of pediocin on the one hand and the potential health hazards associated with consumption of meat products on the other hand, this review aimed to investigate the possible application of pediocin in preservation of meat and meat products against L. monocytogenes.

Listeria monocytogenes Contamination Characteristics in Two Ready-to-Eat Meat Plants From 2019 to 2020 in Shanghai

Listeria monocytogenes is a ubiquitous foodborne pathogen that causes listeriosis and is mostly linked to consumption of ready-to-eat (RTE) foods. Lack of hygiene in food processing environments may be a primary reason for contamination by L. monocytogenes isolates. In this study, L. monocytogenes strains isolated from two RTE meat processing plants in the Shanghai municipality, China, were characterized during 2019–2020 using pulsed-field gel electrophoresis and whole-genome sequencing. Results showed that 29 samples (12.2%) out of 239 were positive for L. monocytogenes, with 21 (18.9%) and 8 (6.25%) isolates from plants A and B, respectively. The packaging room at plant A had the most contamination (14, 48.3%; p < 0.05), with a peak occurrence of 76.5% in processing environments. Nineteen L. monocytogenes isolates belonging to the pulsotype (PT) 7 group were indistinguishable (≥ 95.7%). Furthermore, core-genome multiple loci sequencing typing identified up to nine allelic differences, and the closet pairwise differences among these ST5 isolates included 0–16 small nucleotide polymorphisms. Therefore, L. monocytogenes likely persisted at plant A during 2019–2020 with ongoing clone transmission. In contrast, no L. monocytogenes isolates were identified from processing environments at plant B. Most L. monocytogenes isolates were sampled from raw materials (62.5%). Several isolates (ST378, ST8, and ST120) were detected only once in 2020 and were considered as transient isolates. However, three ST121 isolates with the same PT (PT2) were detected in 2020 and should be noted for their stronger survival ability in harsh environments. These results suggest that continuous monitoring, stringent surveillance, and source tracking are crucial to guaranteeing food safety in RTE food plants.