Whole-Genome Sequence of Salmonella enterica Serovar Bispebjerg from Turkey Reveals Its Pathogenic Potential.

We report the genome sequence of a Salmonella enterica subsp. enterica serovar Bispebjerg strain that was isolated from a turkey flock in 2011. The genome analysis of the strain, a rare and multihost serovar, revealed its pathogenic potential due to antimicrobial resistance and a plethora of Salmonella pathogenicity islands and virulence factors.

Antibiotic resistance genes load in an antibiotic free organic broiler farm.

Antibiotic resistance is a serious concern for public health. Farm environments are relevant reservoirs of antibiotic resistant bacteria and antibiotic resistance genes (ARGs), thus strategies to limit the spread of ARGs from farms to the environment are needed. In this study a broiler farm, where antibiotics have never been used for any purpose, was selected to evaluate if this measure is effective in reducing the ARGs load in farm environment (FE) and in meat processing environment (MPE). Faecal samples from FE and MPE were processed for DNA extraction. Detection and quantification of the 16S rRNA gene and selected ARGs (blaTEM, qnrS, sul2, and tetA) were carried out by PCR and digital droplet PCR (ddPCR), respectively. Generally, the relative abundance of the quantified ARGs in FE was similar or higher than that measured in intensive farms. Furthermore, apart for tetA, no differences in relative abundances of the other ARGs between FE and MPE were determined. These results suggest that the choice to not use antibiotics in broiler farming is not so effective to limit the ARGs spread in MPE and that further sources of ARGs should be considered including the preceding production phase with particular reference to the breeding stage.

Corrigendum: Overview of Control Programs for Twenty-Four Infectious Cattle Diseases in Italy.

[This corrects the article DOI: 10.3389/fvets.2021.665607.].

A Strong Evidence Outbreak of Salmonella Enteritidis in Central Italy Linked to the Consumption of Contaminated Raw Sheep Milk Cheese.

Salmonellosis is the second most commonly reported gastrointestinal infection in humans after campylobacteriosis, and an important cause of foodborne outbreaks in the EU/EEA. The vast majority (72.4%) of the salmonellosis foodborne outbreaks reported in EU in 2019 were caused by Salmonella Enteritidis, even if their total number due to this serovar decreased. In spring 2020, a foodborne outbreak of S. Enteritidis occurred in the Marche region (Central Italy), involving 85 people. The common exposure source was a cheese, pecorino "primo sale", produced with raw sheep milk. The cheese batches were produced by two local dairies, with a livestock production facility, also including a sheep farm, being part of one dairy. Bacteriological analysis of samples collected allowed the detection of S. Enteritidis in animal faeces, environmental samples, raw-milk bulk tanks and milk taken from single animals. These data confirm that, despite the scarce scientific evidence, S. Enteritidis can infect sheep and be shed into the animals' milk. Hence, this is a real risk for public health when unpasteurized milk is used in production of such cheese. The present paper describes the results of the investigations conducted to clarify this outbreak.

Trend of Salmonella enterica occurrence and serotypes in Sardinian pig slaughterhouses.

The aim of this study was to evaluate Salmonella prevalence and serotypes in four Sardinian pig slaughterhouses. Moreover, a population study was conducted with pulsed field gel electrophoresis (PFGE). The results were compared with previous investigations carried out during years 2008 and 2014. A total of 147 samples were collected, 117 from slaughtered pigs (lymph nodes, colon content and carcass surface) and 30 from the slaughterhouse environment (surfaces in contact and not in contact with meat). Salmonella was isolated from 3.4% pig samples and was not detected from environmental samples. Comparing the results with those of previous investigations, occurrence showed a sharp decrease through the years in both animals (18.8% in 2008, 10% in 2014 and 3.4% in 2020) and environmental samples (34.1% in 2008, 3.7 in 2014, and 0% in 2020). At the same time, prevalence of carriers (pigs positive at lymph nodes and/or colon content level) showed a reduction through the years and was always lower in animals coming from local farms rather than those coming from other European Member States, probably indicating the role of stressful factors as transport in increasing Salmonella susceptibility and shedding. Salmonella serotypes were monophasic Typhimurium, Rissen and Muenchen. Overall, 13 different Salmonella serotypes were identified during the three surveys with the most prevalent being serotypes often isolated from slaughtered pigs and during human salmonellosis cases: S. Derby and S. Typhimurium in 2008, S. Anatum and S. Rissen in 2014, monophasic S. Typhimurium in 2020. Population study with pulsed field gel electrophoresis showed a high similarity between Salmonella strains belonging to the same serotype. The results of the investigations showed a decrease of Salmonella occurrence during twelve years in Sardinia, probably due to the improvement in the application of correct GMPs and GHPs at slaughterhouse and also to a reduction of the rate of carrier pigs at farm level.

The challenging task to select Salmonella target serovars in poultry: the Italian point of view.

According to the European Food Safety Authority (EFSA) and European Centre for Disease Prevention and Control (ECDC) annual report, human salmonellosis is mostly related to consumption of contaminated poultry products. Since 2003 in Europe, the Salmonella serovars considered relevant for human health and subject to control in breeding hens of Gallus gallus are: S. Enteritidis, S. Typhimurium (including the monophasic variant), S. Infantis, S. Hadar and S. Virchow. Herein, we investigated the Italian epidemiological situation from 2016 to 2018, comparing Salmonella serovar distributions in humans and poultry, in order to identify the target Salmonella serovars that, if controlled, would potentially have the largest public health impact in Italy. The results showed that control of S. Virchow and S. Hadar does no longer seem to be a priority in Italy and that S. Napoli and S. Derby, which are not included in the group of EU target serovars, are among the most frequent serovars isolated from humans in Italy. While S. Derby has its main reservoir in pigs, S. Napoli does not have a specific reservoir. However, because this serovar is frequently isolated from breeding poultry flocks and is characterised by causing severe human illness, it is a potential target Salmonella serovar in breeding hens of Gallus gallus in Italy.

Overview of Control Programs for Twenty-Four Infectious Cattle Diseases in Italy

The cattle industry is a major driving force for the Italian agricultural sector totalling about 5. 6 million heads for dairy and meat production together. It is particularly developed in the northern part of the country, where 70% of the whole Italian cattle population is reared. The cattle industry development in the rest of the country is hampered by the hard orography of the territories and a variety of socioeconomic features leading to the persistence of the traditional rural farming systems. The differences in the farming systems (industrial vs. traditional) also affect the health status of the farms. Whereas, Enzootic Bovine Leukosis (EBL) is almost eradicated across the whole country, in Southern Italy where Bovine Tuberculosis and Brucellosis are still present and Bluetongue is endemic due to the presence of the competent vector (Culicoides imicola), less investments are aimed at controlling diseases with economic impact or at improving farm biosecurity. On the other hand, with the eradication of these diseases in most part of the country, the need has emerged for reducing the economic burden of non-regulated endemic disease and control programs (CPs) for specific diseases have been implemented at regional level, based on the needs of each territory (for instance common grazing or trading with neighboring countries). This explains the coexistence of different types of programs in force throughout the country. Nowadays in Italy, among cattle diseases with little or no EU regulations only three are regulated by a national CP: Enzootic Bovine Leukosis, Bluetongue and Paratuberculosis, while Bovine Genital Campylobacteriosis and Trichomonosis are nationwide controlled only in breeding bulls. For some of the remaining diseases (Infectious Bovine Rhinotracheitis, Bovine Viral Diarrhea, Streptococcus agalactiae) specific CPs have been implemented by the regional Authorities, but for most of them a CP does not exist at all. However, there is a growing awareness among farmers and public health authorities that animal diseases have a major impact not only on the farm profitability but also on animal welfare and on the use of antibiotics in livestock. It is probable that in the near future other CPs will be implemented.

The Interplay between Campylobacter and the Caecal Microbial Community of Commercial Broiler Chickens over Time.

Campylobacter is the most frequent foodborne zoonotic bacteria worldwide, with chicken meat being overwhelmingly the most important reservoir for human infections. Control measures implemented at the farm level (i.e., biosecurity or vaccination), which have been successfully applied to limit other pathogens, such as Salmonella, have not been effective in reducing Campylobacter occurrence. Thus, new approaches are needed to fully understand the ecological interactions of Campylobacter with host animals to effectively comprehend its epidemiology. The objective of this study was to analyse longitudinally the gut microbiota composition of Campylobacter-infected and non-infected farms to identify any difference that could potentially be indicative of gut colonization by Campylobacter spp. Differences in the colonization rate and timing were observed at the farms that became positive for Campylobacter jejuni over the investigated time points, even though in positive tests, the occurrence of Campylobacter jejuni gut colonization was not observed before the second week of the life of the birds. Significant differences were observed in the abundances of specific bacterial taxa between the microbiota of individuals belonging to farms that became Campylobacter positive during the study and those who remained negative with particular reference to Bacteroidales and Clostridiales, respectively. Moreover, Campylobacter colonization dramatically influenced the microbiota richness, although to a different extent depending on the infection timing. Finally, a key role of Faecalibacterium and Lactobacillus genera on the Campylobacter microbial network was observed. Understanding the ecology of the Campylobacter interaction with host microbiota during infection could support novel approaches for broiler microbial barrier restoration. Therefore, evidence obtained through this study can be used to identify options to reduce the incidence of infection at a primary production level based on the targeted influence of the intestinal microbiota, thus helping develop new control strategies in order to mitigate the risk of human exposure to Campylobacter by chicken meat consumption.

Natural immunity in conventionally and organically reared turkeys and its relation with antimicrobial resistance.

Suboptimal animal welfare may affect natural immunity, rendering animals more susceptible to environmentally conditioned diseases, including those requiring antimicrobial treatment, which may promote antimicrobial resistance (AMR) in bacterial populations. Herewith, we tested the hypothesis that conventionally raised turkeys have higher levels of AMR in indicator Escherichia coli bacteria, but lower levels of natural immunity, as compared to turkeys reared under organic conditions. Litter and serum samples were collected from 28 conventional and 4 organic turkey farms: E. coli isolates from litter were tested for resistance to 14 antimicrobials, while 3 parameters of natural immunity (i.e., lysozyme, hemolytic complement levels, and serum bactericidal activity) were assessed in the sera. Resistant E. coli isolates were identified in both conventional and organic farms but generally more frequently in conventional farms. High rates of resistance to ampicillin (96%), tetracycline (95%), streptomycin (82%), sulfamethoxazole (80%), ciprofloxacin (73%), and trimethoprim (71%), as well as high rates of multiresistance, were observed in conventional farms. Organically raised turkeys had significantly higher levels of lysozyme and serum bactericidal activity than conventional turkeys, and these levels were also higher in turkeys housed in farms where AMR frequency was lower. Findings support the hypothesis that conventional farming conditions may affect turkeys' natural immunity, rendering the animals more susceptible to environmentally conditioned diseases requiring antimicrobial treatment, which would in turn promote AMR. Reducing AMR in turkey farming is therefore more likely to be successful when considering animal welfare as an option to reduce the need of antimicrobial use.

Characterizing Salmonella enterica Serovar Choleraesuis, var. Kunzendorf: A Comparative Case Study.

Different Salmonella serovars generally display different antigenic formulae, but there are some exceptions. For instance, the same antigenic formula, 6,7:c:1,5, is shared by Salmonella enterica serovar, Paratyphi C, Typhisuis, and Choleraesuis. Moreover, three biotypes have been described within the S. Choleraesuis serovar. A distinction among such biotypes can only be based on biochemical behaviors (biotyping) posing serious concerns when rapid characterization is required. The study of an outbreak of severe epizootic salmonellosis in wild boars occurred in Italy between 2012 and 2014 and the typing of the isolates recovered from the outbreak were used to test different approaches for serovar identification. A number of 30 S. Choleraesuis var. Kunzendorf isolates from the outbreak were typed by means of four different methods to derive serovar and biotype: (i) slide agglutination method followed by biochemical tests, (ii) suspension array xMAP® Salmonella Serotyping Assay (SSA), (iii) whole genome sequencing (WGS) and data analysis using SeqSero tool, and (iv) WGS and data analysis using Salmonella TypeFinder tool. Slide agglutination, xMAP® SSA and WGS, followed by SeqSero analysis, are methods that infer the serovars according to the White-Kauffmann-Le Minor (WKL) scheme, based exclusively on antigens. Using these methods, isolates with incomplete antigenic formulae could be misleadingly excluded from an outbreak. On the contrary, WGS followed by Salmonella TypeFinder data analysis, which predicts the serotype on the basis of Multilocus sequence typing (MLST), might be able to cluster together isolates belonging to the same outbreak irrespective of the antigenic formula. Results suggest the benefit of routine use of a combination of in silico MLST and antigenic formula analysis to solve specific ambiguous case studies for outbreak investigation purposes.

Evaluation and quantification of antimicrobial residues and antimicrobial resistance genes in two Italian swine farms.

Antimicrobial resistance genes (ARGs) are considered emerging environmental pollutants, posing potential risks for human and animal health: the misuse of antimicrobials in food-producing animals could favour the maintenance and spread of resistances in bacteria. The occurrence of ARGs in Italian swine farming - which has specific characteristics - was investigated in order to explore resistance spread dynamics. Two farrow-to-finish pig farms were longitudinally monitored: faecal samples from animals and environmental samples were collected. DNA was extracted and tetA, ermB, qnrS and mcr1 ARGs were analysed by qPCR for their ability to confer resistance to highly or critically important antimicrobials (CIAs). Moreover, 16SrDNA gene was analysed to assess bacterial abundance. ermB and tetA genes were found in animal samples and manure samples. On the contrary, mcr1 was exclusively found in weaners, while qnrS occurred in all animal categories but sows and finishers. Among the analysed genes, ermB and tetA showed the highest absolute and relative abundances. Our results indicate that ermB and tetA ARGs are widely disseminated in the explored farms, suggesting efficient maintenance among bacteria and persistence in the environment. Interestingly, the presence of qnrS and mcr1, limited to just a few animal categories, highlights inefficient dissemination of these genes in the farm environment, in particular for mcr1, a stable plasmid gene conferring resistance to the last-resort antimicrobial, colistin. Paying close attention only to the finishing phase would have hampered the discovery of resistances to CIAs at farm level, which we instead identified thanks to an intensive longitudinal monitoring programme.

Different Resolution Power of Multilocus Variable-Number Tandem Repeat Analysis and Whole-Genome Sequencing in the Characterization of S. 1,4,[5],12:i:- Isolates.

Salmonella enterica serovar 1,4,[5],12:i:- has emerged over the last two decades as one of the most common serovars causing human salmonellosis in Europe. It is supposed to originate from Salmonella enterica serovar Typhimurium due to antigenic and genotypic similarities between the two serovars. Due to the high level of similarity, the multilocus variable-number tandem repeat analysis (MLVA) protocol designed for Salmonella Typhimurium routine typing is commonly used also for the characterization of S. 1,4,[5],12:i. Nevertheless, the Salmonella Typhimurium-based MLVA protocol often shows poor discriminatory power for S. 1,4,[5],12:i. Indeed, only a limited number of MLVA profiles have been described for S. 1,4,[5],12:i:-. Moreover, based on the MLVA clustering, S. 1,4,[5],12:i:- is supposed to display high clonality. The aim of the present work was to assess whether the five loci of Salmonella Typhimurium investigated by MLVA are sufficiently accurate to correctly assign S. 1,4,[5],12:i:- isolates. For this purpose, 38 epidemiologically unrelated S. 1,4,[5],12:i:- were subjected to whole-genome sequencing. Isolates were selected among a collection of monophasic strains isolated in Italy from different sources over the period 2014-2016 and belonging to the five most commonly detected MLVA profiles. Results confirmed the possible clonality for S. 1,4,[5],12:i:- serovar in the light of the scarce difference observed in terms of single-nucleotide polymorphisms (SNPs) among investigated isolates. Nevertheless, unrelated isolates on the basis of the difference of SNP number were characterized as indistinguishable by MLVA profile, thus suggesting an insufficient resolution of MLVA. Hence, we can conclude that MLVA-based approach does not seem a valuable proxy to deepen into the epidemiological relationship among S. 1,4,[5],12:i:- isolates. These evidences can be useful to avoid incorrect assignment especially when surveillance data are used for outbreak investigations.

Assessing antimicrobial resistance gene load in vegan, vegetarian and omnivore human gut microbiota.

Massive antimicrobial use in animal farming is considered as the greatest contributor to the presence of antimicrobial-resistant bacteria (ARB) in food of animal origin. Nevertheless, sewage from treated animals may impact on vegetables grown on fertilised fields, but it is largely unknown whether and to what extent ARB are transferred to vegetables and the human gut. It could be hypothesised that food of animal and vegetal origin have a different role in ARB transfer to the human gut and that different diets could be characterised by different antimicrobial resistance gene (ARG) loads. This study included three groups comprising vegans (n = 26), vegetarians (n = 32) and omnivores (n = 43). Metadata regarding food consumption and anthropometric parameters were collected. Gut microbial communities were investigated by 16S rDNA analysis. Four ARGs (sul2, tetA, blaTEM and strB) were quantified by qPCR. The results showed a lower total load of investigated ARGs in vegan diet (pairwise comparison adjusted results: omnivorous-vegan, P = 0.0119; omnivorous-vegetarian, P = 0.7416; and vegan-vegetarian, P = 0.0119). No significant differences in abundance of each gene separately were found between the three groups. Neither the amount of animal protein nor the occurrence of ARGs was significant in explaining differences in the gut microbial community of individuals, and a large proportion of the differences between community composition (PERMANOVA, 46.87%) was not explained by the analysed variables. The results support the role of omnivorous and vegetarian diets in accumulating ARGs, suggesting a possible role for animal-derived food consumption.

Salmonella serovar distribution from non-human sources in Italy; results from the IT-Enter-Vet network.

The study summarises the results obtained over the period 2002-2013 by the Italian IT-Enter-Vet network, aimed at collecting data on Salmonella isolates from non-human sources. A total of 42,491 Salmonella isolates were reported with a progressive decrease over the years. S. Typhimurium was the most frequent serovar up to 2011, but then, it was overtaken by S. 4,[5],12,:i:-, S. Derby, S. Livingstone and S. Enteritidis alternated as the third most commonly isolated serovars. With regard to the sources of isolation, S. Typhimurium was distributed ubiquitously among the animal species. On the contrary, S. 4,[5],12,:i:- and S. Derby were strictly associated with pigs, whereas S. Livingstone, S. Enteritidis and S. Infantis were clearly related to poultry. Intriguingly, when the frequency of serovar distribution along the food chain was considered, it was evident that S. Typhimurium and S. Derby tended to persist along the chain, as they were isolated even more frequently from foods than from animals. A similar distribution was found for S. Enteritidis and S. Hadar. Despite limitations related to non-mandatory participation of laboratories in the network, the data presented are valuable to obtain a picture of the evolution of Salmonella from non-human sources over time in Italy.

Usefulness of indicator bacteria as potential marker of Campylobacter contamination in broiler carcasses.

According to Regulation (EC) No 2017/1495, amending Regulation (EC) No 2073/2005, a slaughterhouse process hygiene criterion based on a limit of 103 CFU/g of Campylobacter for no more than 20 (for the years 2018 and 2019), 15 (for the years 2020-2024) and 10 (starting from 2025) of 50 neck skin samples of broiler carcasses could be an effective measure to reduce the incidence of human campylobacteriosis. In order to stimulate the poultry industry to improve the control of Campylobacter along the slaughter-line, the quantification of indicator bacteria such as Escherichia coli or Enterobacteriaceae could be a useful strategy. The aims of this study were: a) to investigate the possible relationship between Campylobacter and indicator bacteria counts at two different points of the broiler slaughter-line and b) to evaluate the probability that carcasses have Campylobacter counts above 103 CFU/g in relation to indicator bacteria counts. E. coli, Enterobacteriaceae and Campylobacter were simultaneously enumerated on neck skin samples of broiler carcasses sampled at the post-evisceration (n = 75) and at the post-chilling points (n = 75) of three Italian poultry slaughterhouses. In general, the log counts of all the investigated microorganisms were significantly lower at the post-chilling point, and the indicator bacteria (E. coli and Enterobacteriaceae) counts were significantly higher than Campylobacter counts at both sampling points. A multilevel linear mixed model, relating the Campylobacter log10 counts with the E. coli and Enterobacteriaceae log10 counts, showed that the Campylobacter log10 counts increased significantly for every additional E. coli log10 count, and this was more evident at the post-chilling than at the post-evisceration sampling point. With regards to the Enterobacteriaceae, the increase was similar at the two sampling points. An additional model, developed to assess the probability that carcasses would have Campylobacter counts above 3 log10 CFU/g, showed that this probability increased significantly if the level of E. coli count also increased. Carcasses classified as Campylobacter > 3 log10 CFU/g according to the observed results of E. coli ≥ 4 log10 CFU/g did have high Campylobacter counts. Conversely, it was not possible to conclude anything for carcasses with E. coli < 4 log10 CFU/g. These findings support the hypothesis that the monitoring of poultry carcasses for E. coli load could be useful to identify those heavily contaminated with Campylobacter, in order to implement control measures on the farms of origin of such batches, or improving the slaughter process of the plants where the heavily contaminated batches are found.

Assessing the Influence of Vegan, Vegetarian and Omnivore Oriented Westernized Dietary Styles on Human Gut Microbiota: A Cross Sectional Study.

Diet and lifestyle have a strong influence on gut microbiota, which in turn has important implications on a variety of health-related aspects. Despite great advances in the field, it remains unclear to which extent the composition of the gut microbiota is modulated by the intake of animal derived products, compared to a vegetable based diet. Here the specific impact of vegan, vegetarian, and omnivore feeding type on the composition of gut microbiota of 101 adults was investigated among groups homogeneous for variables known to have a role in modulating gut microbial composition such as age, anthropometric variables, ethnicity, and geographic area. The results displayed a picture where the three different dietetic profiles could be well distinguished on the basis of participant's dietetic regimen. Regarding the gut microbiota; vegetarians had a significantly greater richness compared to omnivorous. Moreover, counts of Bacteroidetes related operational taxonomic units (OTUs) were greater in vegans and vegetarians compared to omnivores. Interestingly considering the whole bacterial community composition the three cohorts were unexpectedly similar, which is probably due to their common intake in terms of nutrients rather than food, e.g., high fat content and reduced protein and carbohydrate intake. This finding suggests that fundamental nutritional choices such as vegan, vegetarian, or omnivore do influence the microbiota but do not allow to infer conclusions on gut microbial composition, and suggested the possibility for a preferential impact of other variables, probably related to the general life style on shaping human gut microbial community in spite of dietary influence. Consequently, research were individuals are categorized on the basis of their claimed feeding types is of limited use for scientific studies, since it appears to be oversimplified.

Transfer Study of Silver Nanoparticles in Poultry Production.

Silver nanoparticles (AgNPs) are of interest due to their antimicrobial activity and are seen as potential candidates to replace antibiotics in animal husbandry. A few studies have focused on this new application, but they lack any considerations about residual accumulation of AgNPs in edible animal tissues and animal products. In this research, a 22 day in vivo study was carried out by oral administration of 20 nm spherical PVP coated AgNPs to hens. Six doses of approximately 1 mg kg-1 of AgNPs-PVP each were administered to animals throughout the experimentation. Atomic absorption spectroscopy (AAS) was used for quantitative determination of residual total Ag in different organs and matrices. The analyses showed that Ag accumulates in livers (concentration ranging from 141 µg kg-1 to 269 µg kg-1) and yolks (concentration ranging from 20 µg kg-1 to 49 µg kg-1) but not in muscles, kidneys, and albumen belonging to hens of the treated group (tG2). Ag was not detected in animals of the control group (uG1) (i.e., total Ag < LOD = 10 µg kg-1). Single particle inductively coupled plasma mass spectrometry (spICP-MS) and scanning electron microscopy with energy dispersive X-ray detection (SEM-EDX) were employed to elucidate the presence of AgNPs in livers and yolks belonging to tG2 animals. spICP-MS highlighted that part of residual Ag found in livers (about 5-20%) is in NP form with an average dimension of approximately 20 nm. SEM-EDX technique confirmed the presence of AgNPs only in livers of treated animals. The results show that feeding AgNPs to hens may become a source of consumer exposure to AgNPs. As far as we know this is the first study showing transfer of AgNPs or reaction products thereof from animal feed to animal products.

Resistance to Biocides in Listeria monocytogenes Collected in Meat-Processing Environments.

The emergence of microorganisms exerting resistance to biocides is a challenge to meat-processing environments. Bacteria can be intrinsically resistant to biocides but resistance can also be acquired by adaptation to their sub-lethal concentrations. Moreover, the presence of biocide resistance determinants, which is closely linked to antibiotic resistance determinants, could lead to co-selection during disinfection practices along the food chain, and select cross-resistant foodborne pathogens. The purpose of this work was to test the resistance of wild strains of Listeria monocytogenes, isolated from pork meat processing plants, toward benzalkonium chloride (BC), used as proxy of quaternary ammonium compounds. Furthermore, the expression of two non-specific efflux pumps genes (lde and mdrL) under biocide exposure was evaluated. L. monocytogenes were isolated from five processing plants located in the Veneto region (northeast of Italy) before and after cleaning and disinfection (C&D) procedures. A total of 45 strains were collected: 36 strains before and nine after the C&D procedures. Collected strains were typed according to MLST and ERIC profiles. Strains sampled in the same site, isolated before, and after the C&D procedures and displaying the same MLST and ERIC profiles were tested for their sensitivity to different concentrations of BC, in a time course assay. The expression of non-specific efflux pumps was evaluated at each time point by qPCR using tufA gene as housekeeping. A differential expression of the two investigated genes was observed: lde was found to be more expressed by the strains isolated before C&D procedures while its expression was dose-dependent in the case of the post C&D procedures strain. On the contrary, the expression of mdrL was inhibited under low biocidal stress (10 ppm BC) and enhanced in the presence of high stress (100 ppm BC). These findings suggests a possible role for C&D procedures to select L. monocytogenes persisters, pointing out the importance of dealing with the identification of risk factors in food plants sanification procedures that might select more tolerant strains.