Antimicrobial susceptibility and antibiotic resistance gene transfer analysis of foodborne, clinical, and environmental Listeria spp. isolates including Listeria monocytogenes

Listeria monocytogenes in beef: a hidden risk

Listeria monocytogenes in beef receives less attention compared to other pathogens such as Salmonella and Escherichia coli. To address this gap, we conducted a literature review focusing on the presence of L. monocytogenes in beef. This review encompasses the pathogenic mechanisms, routes of contamination, prevalence rates, and the laws and regulations employed in various countries. Our findings reveal a prevalence of L. monocytogenes in beef and beef products ranging from 2.5% to 59.4%. Notably, serotype 4b was most frequently isolated in cases of beef contamination during food processing, with the skinning and evisceration stages identified as critical points of contamination.

Occurrence and Multidrug Resistance in Strains of Listeria monocytogenes Recovered from the Anaerobic Co-Digestion Sludge Contained in a Single Stage Steel Biodigester: Implications for Antimicrobial Stewardship

L. monocytogenes is a zoonotic foodborne pathogen with inherent adaptability to tolerate environmental and physiological stresses, thereby causing severe disease outbreaks. Antibiotic resistant foodborne pathogens are a challenge to the food industry. A total of 18 samples were pooled from a bio-digester co-digesting swine manure/pinewood sawdust, and evaluated for the occurrence of bacterium plus total viable counts using the spread plate method. The recovered bacterial isolates were presumptively identified by growth on selective medium and confirmed by biochemical characterisation, leading to the isolation of 43 L. monocytogenes. The isolates were characterized based on their susceptibility to antibiotics via the Kirby-Bauer disc diffusion technique against a panel of 14 antibiotics. Equally, the multiple antibiotic resistance (MAR) index was calculated, and MAR phenotypes generated. The bacterial counts were between 102 and104 cfu/mL. Complete susceptibility (100%) was demonstrated to ampicillin, gentamicin and sulfamethoxazole, which are the drugs of choice in the treatment of listeriosis. In addition, intermediate sensitivity occurred at 25.58% to cefotaxime, and the highest resistance (51.16%) was exhibited against nalidixic acid. The MAR index ranged from 0 to 0.71. Overall, 41.86% of the Listeria isolates displayed multidrug resistance, with 18 different MAR phenotypes, demonstrating CIP, E, C, TET, AUG, S, CTX, NA, AML, NI as the greatest MAR phenotype. It can be concluded that the isolates yielding MAR > 0.2 originated from the farm, where antibiotics had been in routine use. Therefore, strict monitoring of antibiotics use in the farm is crucial to mitigate further increase in antibiotic resistance amongst these bacterial isolates.

Antimicrobial Susceptibility Profile of Pathogenic and Commensal Bacteria Recovered from Cattle and Goat Farms

The use of antibiotics in food animals results to antimicrobial resistant bacteria that complicates the ability to treat infections. The purpose of this study was to investigate the prevalence of pathogenic and commensal bacteria in soil, water, manure, and milk from cattle and goat farms. A total of 285 environmental and 81 milk samples were analyzed for Enterobacteriaceae by using biochemical and PCR techniques. Susceptibility to antibiotics was determined by the Kirby-Bauer disk diffusion technique. A total of 15 different Enterobacteriaceae species were identified from goat and cattle farms. Manure had significantly higher (p < 0.05) Enterobacteriaceae (52.0%) than soil (37.2%), trough water (5.4%), and runoff water (5.4%). There was a significant difference (p < 0.05) in Enterobacteriaceae in goat milk (53.9%) and cow milk (46.2%). Enterobacteriaceae from environment showed 100% resistance to novobiocin, erythromycin, and vancomycin E. coli O157:H7, Salmonella spp., Enterococcus spp., and Listeria monocytogenes displayed three, five, six, and ten. AMR patterns, respectively. NOV-TET-ERY-VAN was the most common phenotype observed in all isolates. Our study suggest that cattle and goat farms are reservoirs of multidrug-resistant bacteria. Food animal producers should be informed on the prudent use of antimicrobials, good agricultural practices, and biosecurity measures.

Antibiotic Resistance Profile of Listeria monocytogenes Recovered from Ready-to-Eat Foods Surveyed in South Africa

ABSTRACT

In recent decades, there has been an increase in the reports of antimicrobial resistance of Listeria monocytogenes, which constitutes a serious threat to the therapeutic management of listeriosis infection. Our study profiled the antibiogram fingerprint of L. monocytogenes isolates (n = 194) recovered from common South African ready-to-eat foods. L. monocytogenes isolates recovered from foods were tested against a panel of 22 antibiotics using the disk diffusion method. Antimicrobial resistance (>50%) against ceftriaxone (53.1%), trimethoprim (56.2%), streptomycin, cefotetan (59.3%), sulfamethoxazole (61.9%), vancomycin, and oxytetracyclines (62.9%) were observed. Thirty of the isolates (15.5%) were resistant against only one or two antibiotics, whereas 162 (83.5%) exhibited phenotypic multiple antibiotic resistance. Only two (1%) of the isolates did not exhibit phenotypic resistance against any antibiotics screened. Multiple antibiotic phenotypes revealed high resistance patterns, and the multiple antibiotic indices were greater than the Krumperman permissible (>0.2) benchmark. Of the 44 genes screened, 22 antimicrobial resistance genes were detected among ready-to-eat food isolates, including resistance determinants that encode sulfonamides (n = 125, 64.4%), β-lactams (n = 86, 44.3%), phenicols (n = 25, 12.9), and aminoglycosides (n = 93, 47.9%) resistance. We conclude that the presence of resistant L. monocytogenes isolates harboring corresponding antimicrobial resistance genes in foods could compromise safety and constitute severe health consequences if consumed.

HIGHLIGHTS

Antimicrobial Resistance of Listeria monocytogenes from Animal Foods to First- and Second-Line Drugs in the Treatment of Listeriosis from 2008 to 2021: A Systematic Review and Meta-Analysis

First-line drugs for the treatment of listeriosis are the same around the world, but particular conditions might reduce their efficacy, including antimicrobial resistance. Therefore, this study aimed to verify, based on a systematic review and meta-analysis, whether the prevalence of antimicrobial resistance in Listeria monocytogenes from animal foods is higher for first- or second-line antimicrobials. From the total of 302 identified studies, 16 met all the eligibility criteria from 2008 to 2021 and were included in this meta-analysis. They comprised a dataset of 1152 L. monocytogenes isolates, obtained from different animal food products, food processing environment, and live animals. The included studies were developed in South America (n = 5), Europe (n = 4), Asia (n = 3), Africa (n = 2), and North America (n = 2), testing a total of 35 different antimicrobials, 11 of them classified as first-line drugs. Complete lack of antimicrobial resistance across the studies (all L. monocytogenes isolates tested as susceptible) was only observed for linezolid, while widespread antimicrobial resistance (all L. monocytogenes isolates tested resistant) was described for amoxicillin, benzylpenicillin, cefoxitin, fusidic acid, imipenem, sulfamethoxazole, and vancomycin. Overall, the meta-analysis results indicated no evidence that antimicrobial resistance in L. monocytogenes isolated from animal-based food is higher for first-line antimicrobials compared to second-line compounds (p=0.37). A greater volume of publication, together with better characterization of the isolates, is still needed for a more precise estimate of the real prevalence of antimicrobial resistance in L. monocytogenes.

High prevalence of antibiotic resistance in pathogenic foodborne bacteria isolated from bovine milk

This study aimed to investigate the prevalence of foodborne pathogenic bacteria in bovine milk, their antibiogram phenotype, and the carriage of antibiotic resistance genes. Raw bovine milk samples (n = 100) were randomly collected from different suppliers in the northwest of Iran. Antibiotic-resistant patterns and the presence of antibiotic resistance genes were evaluated in the isolates. Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, and Salmonella spp. were isolated from 78%, 47%, 25%, and 21% of samples, respectively. All isolates showed high rates of resistance to amoxicillin, penicillin, and cefalexin. The bla_TEM and bla_SHV genes were detected in 50.0% and 6.4% of E. coli isolates, respectively. Also, 28.5% and 19.0% of Salmonella isolates were positive for bla_TEM and bla_SHV. The frequency of mecA and bla_Z in S. aureus isolates was 20.0% and 12.0%, respectively. The high prevalence of bovine milk contamination with antimicrobial-resistant species in this study necessitates precise control on antibiotic prescription in veterinary medicine.

The Saprophytic Lifestyle of Listeria monocytogenes and Entry Into the Food-Processing Environment

Listeria monocytogenes is an environmentally adapted saprophyte that can change into a human and animal bacterial pathogen with zoonotic potential through several regulatory systems. In this review, the focus is on the occurrence of Listeria sensu stricto and sensu lato in different ecological niches, the detection methods, and their analytical limitations. It also highlights the occurrence of L. monocytogenes genotypes in the environment (soil, water, and wildlife), reflects on the molecular determinants of L. monocytogenes for the saprophytic lifestyle and the potential for antibiotic resistance. In particular, the strain-specific properties with which some genotypes circulate in wastewater, surface water, soil, wildlife, and agricultural environments are of particular interest for the continuously updating risk analysis.

The prevalence of Listeria monocytogenes in meat products in Brazil: A systematic literature review and meta-analysis

Listeria monocytogenes, a foodborne pathogen that causes human listeriosis, is commonly found in meat products. This study aimed to estimate the prevalence of L. monocytogenes in a variety of Brazilian meat products, using a meta-analysis of data from the literature. A total of 29 publications from five databases, published between January 1, 2009, and December 31, 2019, were included in the study. Estimated by the random-effects model, the combined prevalence of L. monocytogenes was 13%, ranging from 0 to 59%. The combined prevalence of L. monocytogenes was 14% and 11% for raw meat and ready-to-eat (RTE) meat, respectively. The prevalence of L. monocytogenes was higher in the swine species' meat products and the Southeast region of Brazil. Regarding the type of establishment, it was the retail market that presented the highest combined prevalence rate (19%). The most prevalent serotypes of L. monocytogenes were 4b, 1/2a, 1/2b, and 1/2c. The knowledge of differences in the prevalence levels of L. monocytogenes in different meat products can guide in its efficient control by the competent authorities and by industry.

Prevalence and molecular characterization of Listeria monocytogenes isolated from wastewater of cattle slaughterhouses in Turkey

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.

Impact of spent engine oil contamination on the antibiotic resistome of a tropical agricultural soil

Profiling of hydrocarbon-contaminated soils for antibiotic resistance genes (ARGs) is becoming increasingly important due to emerging realities of their preponderance in hydrocarbon-inundated matrices. In this study, the antibiotic resistome of an agricultural soil (1S) and agricultural soil contaminated with spent engine oil (AB1) were evaluated via functional annotation of the open reading frames (ORFs) of their metagenomes using the comprehensive antibiotic database (CARD) and KEGG KofamKOALA. CARD analysis of AB1 metagenome revealed the detection of 24 AMR (antimicrobial resistance) gene families, 66 ARGs, and the preponderance (69.7%) of ARGs responsible for antibiotic efflux in AB1 metagenome. CARD analysis of 1S metagenome revealed four AMR gene families and five ARGs. Functional annotation of the two metagenomes using KofamKOALA showed 171 ARGs in AB1 and 29 ARGs in 1S, respectively. Majority of the detected ARGs in AB1 (121; 70.8%) and 1S (16; 55.2%) using KofamKOALA are responsible for antibiotic efflux while ARGs for other resistance mechanisms were also detected. All the five major antibiotic efflux pump systems were detected in AB1 metagenome, though majority of the ARGs for antibiotic efflux belong to the RND (resistance-nodulation-cell division) and MFS (major facilitator superfamily) efflux systems. Significant differences observed in the ARGs recovered from 1S and AB1 metagenomes were statistically validated (P < 0.05). SEO contamination is believed to be responsible for ARGs increase in AB1 metagenome via mechanisms of cross-resistance especially with efflux pumps. The detection of these ARGs is of great public health concern in this era of multidrug resistant isolates resurgence.

Whole Genome Analysis of Three Multi-Drug Resistant Listeria innocua and Genomic Insights Into Their Relatedness With Resistant Listeria monocytogenes

Listeria innocua are Gram-positive rod-shaped bacteria, which are not generally infectious as opposed to Listeria monocytogenes. However, the comparatively high genomic similarity between both along with on occasion, their coexistence in similar ecological niches may present the opportunity for resistance or virulence gene transfer. In this study, three multi-drug resistant L. innocua originally cultured from food were put forward for long-read genome sequencing. Chromosome and plasmid genomes were assembled and annotated. Analysis demonstrated that the resistant phenotypes correlated well with genotypes. Three plasmids pLI42, pLI203, and pLI47-1 were identified which harbor resistance islands. Sequence alignments suggested that plasmids pLI42 and pLI203 were highly similar to a previously sequenced L. monocytogenes plasmid pLR1. Similarly, another three types of resistance gene islands were observed on chromosome, including tet(M) gene islands (transposon Tn916 orthologs), dfrG gene islands and optrA-erm(A) gene islands. All three L. innocua isolates possessed listeria pathogenicity island-4 (LIPI-4) which is linked to cases of mengitis. Further genome environment and phylogenic analysis of regions flanking LIPI-4 of L. innocua and L. monocytogenes showed that these may have common origins and with the potential to transmit from the former. Our findings raise the possible need to include both L. monocytogenes and L. innocua in food surveillance programs so as to further understand of the origins of antimicrobial resistance and virulence markers of public health importance in L. monocytogenes.

Characterization of Listeria monocytogenes isolates from lactating dairy cows in a Wisconsin farm: Antibiotic resistance, mammalian cell infection, and effects on the fecal microbiota

Listeria monocytogenes is an invasive foodborne pathogen that is ubiquitously present in the dairy farm environment. Although cattle are a reservoir of L. monocytogenes, most adult animals do not exhibit clinical symptoms, suggesting a homeostasis between this pathogen and the bovine gastrointestinal ecosystem. Nevertheless, substantial prevalence of L. monocytogenes fecal shedding by dairy cattle has been reported in many studies, posing threats of transmission within the herd and contamination of the human food supply. Accordingly, understanding the L. monocytogenes ecology within the bovine gastrointestinal tract is important to prevent clinical illness in the animal host, reduce transmission, and guide intervention strategies. In this study, we conducted a longitudinal sampling of fecal samples from 20 lactating dairy cows in one Wisconsin farm over a 29-d period and found a strikingly high incidence of L. monocytogenes shedding, in 90% of sampled animals. The L. monocytogenes isolates were genetically diverse, representing all common serotypes previously identified from cattle. Additionally, most tested isolates were resistant to ampicillin, and a few were also resistant to gentamicin or trimethoprim/sulfamethoxazole. Most isolates effectively infected human epithelial cells (Caco-2) and murine fibroblasts (L2), suggesting that they are all capable of causing systemic infection if the intestinal barrier is breached. Finally, we investigated the effects of L. monocytogenes colonization on the gastrointestinal tract microbiota by analyzing the fecal bacterial communities of some shedding and nonshedding cows. Whereas L. monocytogenes did not affect the α and β diversity of tested animals, a subset of shedding cows exhibited different abundances of certain operational taxonomic units within the Bacteroidetes and Firmicutes phyla compared with nonshedding cows. Overall, our findings highlight the threat of antibiotic resistance among some L. monocytogenes isolates, emphasize the need for a strain-specific approach in listeriosis treatment, and suggest the potential negative influence of subclinical L. monocytogenes carriage on animal gut health.

Whole-Genome Sequencing-Based Characterization of Listeria monocytogenes from Fish and Fish Production Environments in Poland

Listeria monocytogenes, an important foodborne pathogen, may be present in different kinds of food and in food processing environments where it can persist for a long time. In this study, 28 L. monocytogenes isolates from fish and fish manufactures were characterized by whole genome sequencing (WGS). Core genome multilocus sequence typing (cgMLST) analysis was applied to compare the present isolates with publicly available genomes of L. monocytogenes strains recovered worldwide from food and from humans with listeriosis. All but one (96.4%) of the examined isolates belonged to molecular serogroup IIa, and one isolate (3.6%) was classified to serogroup IVb. The isolates of group IIa were mainly of MLST sequence types ST121 (13 strains) and ST8 (four strains) whereas the isolate of serogroup IVb was classified to ST1. Strains of serogroup IIa were further subtyped into eight different sublineages with the most numerous being SL121 (13; 48.1% strains) which belonged to six cgMLST types. The majority of strains, irrespective of the genotypic subtype, had the same antimicrobial resistance profile. The cluster analysis identified several molecular clones typical for L. monocytogenes isolated from similar sources in other countries; however, novel molecular cgMLST types not present in the Listeria database were also identified.

A review of Listeria monocytogenes from meat and meat products: Epidemiology, virulence factors, antimicrobial resistance and diagnosis

Listeria monocytogenes is a zoonotic food-borne pathogen that is associated with serious public health and economic implications. In animals, L. monocytogenes can be associated with clinical listeriosis, which is characterised by symptoms such as abortion, encephalitis and septicaemia. In human beings, listeriosis symptoms include encephalitis, septicaemia and meningitis. In addition, listeriosis may cause gastroenteric symptoms in human beings and still births or spontaneous abortions in pregnant women. In the last few years, a number of reported outbreaks and sporadic cases associated with consumption of contaminated meat and meat products with L. monocytogenes have increased in developing countries. A variety of virulence factors play a role in the pathogenicity of L. monocytogenes. This zoonotic pathogen can be diagnosed using both classical microbiological techniques and molecular-based methods. There is limited information about L. monocytogenes recovered from meat and meat products in African countries. This review strives to: (1) provide information on prevalence and control measures of L. monocytogenes along the meat value chain, (2) describe the epidemiology of L. monocytogenes (3) provide an overview of different methods for detection and typing of L. monocytogenes for epidemiological, regulatory and trading purposes and (4) discuss the pathogenicity, virulence traits and antimicrobial resistance profiles of L. monocytogenes.

Antimicrobial Susceptibility and Multilocus Sequence Typing of Listeria monocytogenes Isolated Over 11 Years from Food, Humans, and the Environment in Italy

Due to the increasing number of studies reporting the detection of antimicrobial-resistant isolates of Listeria monocytogenes, we sought to determine the antimicrobial susceptibility of L. monocytogenes isolates collected in Italy and find potential correlations to their serotypes and multilocus sequence types (MLST). The antimicrobial susceptibility of 317 L. monocytogenes isolates collected from food, humans, and the environment from 1998 to 2009 was assessed by minimum inhibitory concentration (MIC). Serotyping and MLST was also performed on all isolates. Potential correlations among antimicrobial resistance profiles, serotyping, and MLST were statistically evaluated. Twenty-four percent of L. monocytogenes isolates were resistant to oxacillin, 28.7% intermediate to clindamycin, and 24.3% to ciprofloxacin. The majority of isolates with elevated MIC to oxacillin was of environmental origin and belonged to serotype 4b/4e and ST2. Isolates with intermediate MIC values to clindamycin and ciprofloxacin were mostly of food and human origin and belonged to serotype 4b/4e and ST9. Regarding the time frame of isolate collection, comparing the last 3 years (2007-2009) to previous years (1998-2006), an increase was observed in the percentage of resistant and intermediate isolates per year. This trend strongly suggests the need for increasing attention on the prevalence of antimicrobial resistance in L. monocytogenes in Italy. To predict future resistance trends, the monitoring of clinical intermediate resistance might represent a useful tool especially for antibiotics associated to multiple-step mechanisms of acquired resistance. A specific focus should be addressed to antimicrobial-resistant isolates of serotype 4b, repeatedly associated with food-borne outbreaks.

Characterization of antibiogram fingerprints in Listeria monocytogenes recovered from irrigation water and agricultural soil samples

Listeria monocytogenes (L. monocytogenes) is a foodborne pathogen and the etiologic agent of listeriosis, which can be disseminated within the agricultural environment particularly soil and irrigation water, contaminate farm produce and cause high mortality and morbidity among vulnerable individuals. This study assessed the incidence and antibiogram of L. monocytogenes recovered from irrigation water and agricultural soil samples collected from Chris Hani and Amathole District Municipalities (DMs) in Eastern Cape Province, South Africa. The distribution of presumptive L. monocytogenes in irrigation water and agricultural soil samples was done using the standard plate count method, while polymerase chain reaction (PCR) was used to identify the isolates. The confirmed isolates were screened for 9 key virulence markers using PCR after which they were subjected to antibiotic susceptibility testing against 18 antibiotics used for the alleviation of listeriosis using the disk diffusion method. Relevant putative antibiotic resistance genes in the resistant variants were screened for using PCR. The distribution of L. monocytogenes in irrigation water samples was statistically significant (P ≤ 0.05) and ranged from log₁₀ 1.00 CFU/100ml to log₁₀ 3.75 CFU/100 ml. In agricultural soil samples, the distribution ranged significantly (P ≤ 0.05) from log₁₀ 2.10 CFU/g to log₁₀ 3.51 CFU/g. Of the 117 presumptive L. monocytogenes recovered from irrigation water samples and 183 presumptive L. monocytogenes isolated from agricultural soil samples, 8 (6.8%) and 12 (6.6%) isolates were confirmed respectively. Nine virulence genes including inlA, inlB, inlC, inlJ, actA, hlyA, plcA, plcB, and iap were detected in all the isolates. The proportion of the isolates exhibiting phenotypic resistance against the test antimicrobials followed the order: tetracycline (90%), doxycycline (85%), cefotaxime (80%), penicillin (80%), chloramphenicol (70%), linezolid (65%), erythromycin (60%) and trimethoprim/sulfamethoxazole (55%). The isolates exhibited multiple antibiotic resistance against 3 or more antibiotics and the MAR indices of all the multidrug isolates were ≥0.2. The isolates harboured antibiotic resistance genes including tetA, tetB, tetC, sulI, sulII, aadA, aac(3)-IIa and ESBLs including bla_TEM, bla_CTX-M group 9, bla_VEBas well as AmpC. None of the isolates harboured the carbapenemases. We conclude that irrigation water and agricultural soil collected from Chris Hani and Amathole District Municipalities (DMs) in Eastern Cape Province of South Africa are reservoirs and potential transmission routes of multidrug-resistant L. monocytogenes to the food web and consequently threat to public health.

Prevalence, Pathogenicity, Virulence, Antibiotic Resistance, and Phylogenetic Analysis of Biofilm-Producing Listeria monocytogenes Isolated from Different Ecological Niches in Egypt: Food, Humans, Animals, and Environment

Serious outbreaks of foodborne disease have been caused by Listeria monocytogenes found in retail delicatessens and the severity of disease is significant, with high hospitalization and mortality rates. Little is understood about the formidable public health threat of L. monocytogenes in all four niches, humans, animals, food, and environment, in Egypt. This study analyzed the presence of L. monocytogenes collected from the four environmental niches and bioinformatics analysis was implemented to analyze and compare the data. PCR was used to detect virulence genes encoded by pathogenicity island (LIPI-1). prfA amino acid substation that causes constitutive expression of virulence was common in 77.7% of isolates. BLAST analysis did not match other isolates in the NCBI database, suggesting this may be a characteristic of the region associated with these isolates. A second group included the NH1 isolate originating in China, and BLAST analysis showed this prfA allele was shared with isolates from other global locations, such as Europe and North America. Identification of possible links and transmission pathways between the four niches helps to decrease the risk of disease in humans, to take more specific control measures in the context of disease prevention, to limit economic losses associated with food recalls, and highlights the need for treatment options.

Two perspectives of Listeria monocytogenes hazards in dairy products: the prevalence and the antibiotic resistance

Listeria monocytogenes is among the most food-borne pathogens. It has the ability to grow over a range of temperature, including refrigeration temperature. Foods kept in refrigerator more than the prescribed period of time create an opportunity for the occurrence of Listeria monocytogenes. As this review shows, the prevalence of L. monocytogenes has more likely evident in pasteurized milk than other dairy products, such as raw milk. Inadequate temperature and faults in technology during pasteurization can be the disposing factors for the presence of the organism in dairy products. The organism, on the other hand, has been found to be resistant to those commonly known antibiotics that have human and veterinary importance, namely, ampicillin, Tetracycline, and chloramphenicol, streptomycin, erytromycin, penicillin G., and others. Resistance ability of the organism can be mediated by different natural and acquired resistance mechanisms, such as self-transferrable plasmids, mobilizable plasmids, and conjugative transposons. The emergence and spread of antibiotic resistance of L. monocytogenes has serious public health and economic impacts at large. This paper has reviewed the prevalence and the antibiotic resistance of L. monocytogenes isolates of dairy products and the strategic mechanisms of the organism develop resistance against the antibiotics.

Listeria monocytogenes in sliced cheese and ham from retail markets in southern Brazil

The aims of this study were to evaluate the occurrence of Listeria monocytogenes and Salmonella spp. in sliced cheese and ham from retail markets in southern Brazil, as well as to perform molecular characterization and to assess the antimicrobial resistance profile of the isolates. Samples (n = 160) of sliced cheese and ham were collected at retail level from the city of Pelotas, Brazil. The isolation of L. monocytogenes and Salmonella spp. was performed and the isolates were confirmed by PCR, submitted to antimicrobial susceptibility testing and pulsed-field gel electrophoresis (PFGE). Listeria monocytogenes was found in 9.4% (15/160) of the samples. All L. monocytogenes isolates were positive for the prs, inlA, inlC and inlJ genes. Salmonella spp. was not isolated. Regarding the antimicrobial susceptibility, one (6.6%) L. monocytogenes isolate was resistant to streptomycin and four (26.6%) to clindamycin. Macrorestriction analysis with ApaI and AscI enzymes yielded two major PFGE groups I and II. All L. monocytogenes isolates showed virulence genes, and some of them were resistant to clinically used antimicrobials, representing a risk to public health. Moreover, PFGE patterns with high similarity were visualized in L. monocytogenes isolates at different times, demonstrating adaptability of the pathogen at retail level in the region.

Whole-Genome Sequencing-Based Characterization of 100 Listeria monocytogenes Isolates Collected from Food Processing Environments over a Four-Year Period

Listeria monocytogenes is frequently found in foods and processing facilities, where it can persist, creating concerns for the food industry. Its ability to survive under a wide range of environmental conditions enhances the potential for cross-contamination of the final food products, leading to possible outbreaks of listeriosis. In this study, whole-genome sequencing (WGS) was applied as a tool to characterize and track 100 L. monocytogenes isolates collected from three food processing environments. These WGS data from environmental and food isolates were analyzed to (i) assess the genomic diversity of L. monocytogenes, (ii) identify possible source(s) of contamination, cross-contamination routes, and persistence, (iii) detect absence/presence of antimicrobial resistance-encoding genes, (iv) assess virulence genotypes, and (v) explore in vivo pathogenicity of selected L. monocytogenes isolates carrying different virulence genotypes. The predominant L. monocytogenes sublineages (SLs) identified were SL101 (21%), SL9 (17%), SL121 (12%), and SL5 (12%). Benzalkonium chloride (BC) tolerance-encoding genes were found in 62% of these isolates, a value that increased to 73% among putative persistent subgroups. The most prevalent gene was emrC followed by bcrABC, qacH-Tn6188, and qacC. The L. monocytogenes major virulence factor inlA was truncated in 31% of the isolates, and only one environmental isolate (L. monocytogenes CFS086) harbored all major virulence factors, including Listeria pathogenicity island 4 (LIPI-4), which has been shown to confer hypervirulence. A zebrafish embryo infection model showed a low (3%) embryo survival rate for all putatively hypervirulent L. monocytogenes isolates assayed. Higher embryo survival rates were observed following infection with unknown virulence potential (20%) and putatively hypovirulent (53 to 83%) L. monocytogenes isolates showing predicted pathogenic phenotypes inferred from virulence genotypes.IMPORTANCE This study extends current understanding of the genetic diversity among L. monocytogenes from various food products and food processing environments. Application of WGS-based strategies facilitated tracking of this pathogen of importance to human health along the production chain while providing insights into the pathogenic potential for some of the L. monocytogenes isolates recovered. These analyses enabled the grouping of selected isolates into three putative virulence categories according to their genotypes along with informing selection for phenotypic assessment of their pathogenicity using the zebrafish embryo infection model. It has also facilitated the identification of those isolates with genes conferring tolerance to commercially used biocides. Findings from this study highlight the potential for the application of WGS as a proactive tool to support food safety controls as applied to L. monocytogenes.

Pediocin-Like Antimicrobial Peptides of Bacteria

Bacteriocins are bacterial antimicrobial peptides that, unlike classical peptide antibiotics, are products of ribosomal synthesis and usually have a narrow spectrum of antibacterial activity against species closely related to the producers. Pediocin-like bacteriocins (PLBs) belong to the class IIa of the bacteriocins of Gram-positive bacteria. PLBs possess high activity against pathogenic bacteria from Listeria and Enterococcus genera. Molecular target for PLBs is a membrane protein complex - bacterial mannose-phosphotransferase. PLBs can be synthesized by components of symbiotic microflora and participate in the maintenance of homeostasis in various compartments of the digestive tract and on the surface of epithelial tissues contacting the external environment. PLBs could give a rise to a new group of antibiotics of narrow spectrum of activity.

Epidemiology and Clinical Manifestations of Listeria monocytogenes Infection

Listeria monocytogenes is a Gram-positive pathogenic bacterium which can be found in soil or water. Infection with the organism can develop after ingestion of contaminated food products. Small and large outbreaks of listeriosis have been described. Listeria monocytogenes can cause a number of clinical syndromes, most frequently sepsis, meningitis, and rhombencephalitis, particularly in immunocompromised hosts. The latter syndrome mimics the veterinary infection in ruminants called "circling disease". Neonatal infection can occur as a result of maternal chorioamnionitis ("early onset" sepsis) or through passage through a birth canal colonized with Listeria from the gastrointestinal tract. ("late onset" meningitis). Treatment of listeriosis is usually with a combination of ampicillin and an aminoglycoside but other regimens have been used. The mortality rate is high, reflecting the combination of an immunocompromised host and an often delayed diagnosis.

Antimicrobial Resistance in Listeria Species

For nearly a century the use of antibiotics to treat infectious diseases has benefited human and animal health. In recent years there has been an increase in the emergence of antibiotic-resistant bacteria, in part attributed to the overuse of compounds in clinical and farming settings. The genus Listeria currently comprises 17 recognized species found throughout the environment. Listeria monocytogenes is the etiological agent of listeriosis in humans and many vertebrate species, including birds, whereas Listeria ivanovii causes infections mainly in ruminants. L. monocytogenes is the third-most-common cause of death from food poisoning in humans, and infection occurs in at-risk groups, including pregnant women, newborns, the elderly, and immunocompromised individuals.

Phenotypic and Genotypic Analysis of Antimicrobial Resistance among Listeria monocytogenes Isolated from Australian Food Production Chains

The current global crisis of antimicrobial resistance (AMR) among important human bacterial pathogens has been amplified by an increased resistance prevalence. In recent years, a number of studies have reported higher resistance levels among Listeria monocytogenes isolates, which may have implications for treatment of listeriosis infection where resistance to key treatment antimicrobials is noted. This study examined the genotypic and phenotypic AMR patterns of 100 L. monocytogenes isolates originating from food production supplies in Australia and examined this in the context of global population trends. Low levels of resistance were noted to ciprofloxacin (2%) and erythromycin (1%); however, no resistance was observed to penicillin G or tetracycline. Resistance to ciprofloxacin was associated with a mutation in the fepR gene in one isolate; however, no genetic basis for resistance in the other isolate was identified. Resistance to erythromycin was correlated with the presence of the ermB resistance gene. Both resistant isolates belonged to clonal complex 1 (CC1), and analysis of these in the context of global CC1 isolates suggested that they were more similar to isolates from India rather than the other CC1 isolates included in this study. This study provides baseline AMR data for L. monocytogenes isolated in Australia, identifies key genetic markers underlying this resistance, and highlights the need for global molecular surveillance of resistance patterns to maintain control over the potential dissemination of AMR isolates.

Antibiotic susceptibility of 259 Listeria monocytogenes strains isolated from food, food-processing plants and human samples in Germany

BACKGROUND

The objective of this study was to evaluate the susceptibility of 259 Listeria monocytogenes strains isolated from food and food-processing environments and patient samples in Germany to 14 antibiotics widely used in veterinary and human medicine. L. monocytogenes strains were isolated mainly from milk and milk products and classified according to their molecular serotypes IIa (n=112), IIb (n=41), IIc (n=36), IVa (n=1), IVb (n=66), and IVb-v1 (n=3).

METHODS

Susceptibility tests were performed by using the automated 96-well based microdilution system Micronaut-S. Ampicillin, benzylpenicillin, ceftriaxone, ciprofloxacin, daptomycin, erythromcyin, gentamicin, linezolid, meropenem, rifampicin, tetracycline, tigecycline, trimethoprim/sulfamethoxazole and vancomycin were tested in at least five different concentrations.

RESULTS

Among the 259 strains under study, 145 strains revealed multidrug-resistance (resistance to ≥3 antibiotics) and predominantly belonged to serotype IV (59%). Strains were mainly resistant to daptomycin, tigecycline, tetracycline, ciprofloxacin, ceftriaxone, trimethropim/sulfamethoxazole and gentamicin.

CONCLUSIONS

Antibiotic resistance in general and multidrug-resistance in particular were more prevalent in L. monocytogenes strains isolated in Germany compared to similar reference stocks from other European countries and the USA but similar to stocks from China.

Listeria monocytogenes in Food-Processing Facilities, Food Contamination, and Human Listeriosis: The Brazilian Scenario

Listeria monocytogenes is a foodborne pathogen that contaminates food-processing environments and persists within biofilms on equipment, utensils, floors, and drains, ultimately reaching final products by cross-contamination. This pathogen grows even under high salt conditions or refrigeration temperatures, remaining viable in various food products until the end of their shelf life. While the estimated incidence of listeriosis is lower than other enteric illnesses, infections caused by L. monocytogenes are more likely to lead to hospitalizations and fatalities. Despite the description of L. monocytogenes occurrence in Brazilian food-processing facilities and foods, there is a lack of consistent data regarding listeriosis cases and outbreaks directly associated with food consumption. Listeriosis requires rapid treatment with antibiotics and most drugs suitable for Gram-positive bacteria are effective against L. monocytogenes. Only a minority of clinical antibiotic-resistant L. monocytogenes strains have been described so far; whereas many strains recovered from food-processing facilities and foods exhibited resistance to antimicrobials not suitable against listeriosis. L. monocytogenes control in food industries is a challenge, demanding proper cleaning and application of sanitization procedures to eliminate this foodborne pathogen from the food-processing environment and ensure food safety. This review focuses on presenting the L. monocytogenes distribution in food-processing environment, food contamination, and control in the food industry, as well as the consequences of listeriosis to human health, providing a comparison of the current Brazilian situation with the international scenario.

Inhibition of listeriolysin O oligomerization by lutein prevents Listeria monocytogenes infection

The foodborne pathogenic bacterial species Listeria monocytogenes (L. monocytogenes) has caused incalculable damages to public health, and its successful infection requires various virulence factors, including Listeriolysin O (LLO). By forming pores in phagosomal membranes and even in some organelles, LLO plays an indispensable role in the ability of L. monocytogenes to escape from host immune attacks. Because of its critical role, LLO offers an appropriate therapeutic target against L. monocytogenes infection. Here, lutein, a natural small molecule existing widely in fruits and vegetables, is demonstrated as an effective inhibitor of LLO that works by blocking its oligomerization during invasion without showing significant bacteriostatic activity. Further assays applying lutein in cell culture models of invasion and in animal models showed that lutein could effectively inhibit L. monocytogenes infection. Overall, our results indicate that lutein may represent a promising and novel therapeutic agent against L. monocytogenes infection.

Listeria monocytogenes isolates from food and food environment harbouring tetM and ermB resistance genes

Listeria monocytogenes is a foodborne pathogen that has become an important cause of human and animal diseases worldwide. The purpose of this study was to evaluate the serotypes, virulence potential, antimicrobial resistance profile, and genetic relationships of 50 L. monocytogenes isolates from food and food environment in southern Brazil. In this study, the majority of L. monocytogenes isolates belonged to the serotypes 1/2b (42%) and 4b (26%), which are the main serotypes associated with human listeriosis. In addition, all isolates harboured internalin genes (inlA, inlC, inlJ), indicating a virulence potential. The isolates were sensitive to most of the antimicrobial compounds analysed, and five isolates (10%) were multi-resistant. Two isolates harboured antimicrobial resistance genes (tetM and ermB) and in one of them, the gene was present in the plasmid. Moreover, according to the pulsed field gel electrophoresis assay, two multi-resistant isolates were a single clone isolated from food and the processing plant. The isolates were susceptible to the most frequently used antibiotics for listeriosis treatment. However, the presence of multidrug-resistant isolates and antimicrobial resistance genes including in the plasmid could even be transferred between bacterial species, suggesting a potential health risk to consumers and a potential risk of spreading multi-resistance genes to other bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

Listeria monocytogenes is an important agent of foodborne diseases. The results of this study suggest a potential capacity of L. monocytogenes isolates from food and food environment to cause human infections. Antimicrobial multi-resistance profiles were detected in 10%, and two isolates harboured tetM and ermB resistance genes. Moreover, the present research can help to build up a better knowledge about antimicrobial resistance of L. monocytogenes. Additionally, we found one isolate carrying tetM resistance gene in a plasmid, that suggests a possible transmission between commensal and/or other pathogenic bacteria of food environment, thereby raising up concerns regarding bacterial resistance.

Diversity of Listeria monocytogenes Strains of Clinical and Food Chain Origins in Belgium between 1985 and 2014

Listeriosis is a rare but severe disease, mainly caused by Listeria monocytogenes. This study shows the results of the laboratory-based surveillance of Listeriosis in Belgium over the period 1985-2014. Besides the incidence and some demographic data we present also more detailed microbiological and molecular characteristics of human strains isolated since 2000. The strains from the latter period were compared to food and animal strains from the same period. Our study shows that different food matrices were commonly contaminated with L. monocytogenes presenting the same PFGE profile as in patient's isolates. Since 1985, we observed a significant decrease in incidence of the Materno-Neonatal cases (from 0.15 to 0.04 cases /100,000 inhabitants-year), which is probably to be attributed to active prevention campaigns targeting pregnant women. Despite the strengthening of different control measures by the food industry, the incidence of non-Materno-Neonatal listeriosis increased in Belgium (from 0.3 to 0.7 cases /100,000 inhabitants-year), probably due to the rise of highly susceptible patients in an aging population. This significant increase found in non-Materno-Neonatal cases (slope coefficient 7.42%/year, P<0.0001) can be attributed to significant increase in incidence of isolates belonging to serovars 1/2a (n = 393, slope coefficient 6.62%/year, P<0.0001). Although resistance to antimicrobials is rare among L. monocytogenes isolates, a trend to increasing MIC values is evident with chloramphenicol, amoxicillin, tetracycline and ciprofloxacin. We show that fluoroquinolone resistance is not linked to chromosomal mutations, but caused by a variety of efflux pumps. Our study also shows that huge majority of known underlying pathologies (426 out of 785 cases) were cancers (185/426, 43.1%) and haematological malignancies (75/185, 40.5%). Moreover the risk population is susceptible to low levels of contamination in food stressing the need of prevention campaigns specifically targeting these persons.