Predominance of Distinct Listeria Innocua and Listeria Monocytogenes in Recurrent Contamination Events at Dairy Processing Facilities

Genetic diversity of Listeria monocytogenes from seafood products, its processing environment, and clinical origin in the Western Cape, South Africa using whole genome sequencing

Listeria monocytogenes is a concern in seafood and its food processing environment (FPE). Several outbreaks globally have been linked to various types of seafood. Genetic profiling of L. monocytogenes is valuable to track bacterial contamination throughout the FPE and in understanding persistence mechanisms, with limited studies from South Africa. Forty-six L. monocytogenes isolates from origins: Fish/seafood products (n = 32) (salmon, smoked trout, fresh hake, oysters), the FPE (n = 6), and clinical (n = 8) were included in this study. Lineage typing, antibiotic susceptibility testing, and screening for two genes (bcrABC and emrC) conferring sanitizer tolerance was conducted. The seafood and FPE isolates originated from seven different factories processing various seafood products with undetermined origin. All clinical isolates were categorized as lineage I, and seafood and FPE isolates were mostly categorized into lineage II (p < 0.01). Seafood and FPE isolates (53%) carried the bcrABC gene cassette and one fish isolate, the emrC gene. A subset, n = 24, was grouped into serotypes, sequence types (STs), and clonal complexes (CCs) with whole genome sequencing (WGS). Eight CCs and ten STs were identified. All clinical isolates belonged to serogroup 4b, hypervirulent CC1. CC121 was the most prevalent in isolates from food and the FPE. All isolates carried Listeria pathogenicity islands (LIPI) 1 and 2. LIPI-3 and LIPI-4 were found in certain isolates. We identified genetic determinants linked to enhanced survival in the FPE, including stress survival islets (SSI) and genes conferring tolerance to sanitizers. SSI-1 was found in 44% isolates from seafood and the FPE. SSI-2 was found in all the ST121 seafood isolates. Isolates (42%) harbored transposon Tn1688_qac (ermC), conferring tolerance to quaternary ammonium compounds. Five plasmids were identified in 13 isolates from seafood and the FPE. This is the first One Health study reporting on L. monocytogenes genetic diversity, virulence and resistance profiles from various types of seafood and its FPE in South Africa.

Utilizing whole genome sequencing to characterize Listeria spp. persistence and transmission patterns in a farmstead dairy processing facility and its associated farm environment

Farmstead dairy processing facilities may be particularly susceptible to Listeria spp. contamination due to the close physical proximity of their processing environments (PE) to associated dairy farm environments (FE). In this case study, we supported the implementation of interventions focused on improving (i) cleaning and sanitation efficacy, (ii) hygienic zoning, and (iii) sanitary equipment/facility design and maintenance in a farmstead dairy processing facility, and evaluated their impact on Listeria spp. detection in the farmstead's PE over 1 year. Detection of Listeria spp. in the farmstead's PE was numerically reduced from 50% to 7.5% after 1 year of intervention implementation, suggesting that these interventions were effective at improving Listeria spp. control. In addition, environmental samples were also collected from the farmstead's FE to evaluate the risk of the FE as a potential source of Listeria spp. in the PE. Overall, detection of Listeria spp. was higher in samples collected from the FE (75%, 27/36) compared with samples collected from the PE (24%, 29/120). Whole genome sequencing (WGS) performed on select isolates collected from the PE and FE supported the identification of 6 clusters (range of 3 to 15 isolates per cluster) that showed ≤ 50 high quality single nucleotide polymorphism (hqSNP) differences. Of these 6 clusters, 3 (i.e., clusters 2, 4, and 5) contained isolates that were collected from both the PE and FE, suggesting that transmission between these 2 environments was likely. Moreover, all cluster 2 isolates represented a clonal complex (CC) of L. monocytogenes commonly associated with dairy farm environmental reservoirs (i.e., CC666), which may support that the farmstead's FE represented an upstream source of the cluster 2 isolates that were found in the PE. Overall, our data underscore that, while the FE can represent a potential upstream source of Listeria spp. contamination in a farmstead dairy processing facility, implementation of targeted interventions can help effectively minimize Listeria spp. contamination in the PE.

Exploring the occurrence of Listeria in biofilms and deciphering the bacterial community in a frozen vegetable producing environment

The establishment of Listeria (L.) monocytogenes within food processing environments constitutes a significant public health concern. This versatile bacterium demonstrates an exceptional capacity to endure challenging environmental conditions in the food processing environment, where contamination of food products regularly occurs. The diverse repertoire of stress resistance genes, the potential to colonize biofilms, and the support of a co-existing microbiota have been proposed as root causes for the survival of L. monocytogenes in food processing environments. In this study, 71 sites were sampled after cleaning and disinfection in a European frozen vegetable processing facility, where L. monocytogenes in-house clones persisted for years. L. monocytogenes and L. innocua were detected by a culture-dependent method at 14 sampling sites, primarily on conveyor belts and associated parts. The presence of biofilms, as determined by the quantification of bacterial load and the analysis of extracellular matrix components (carbohydrates, proteins, extracellular DNA) was confirmed at nine sites (12.7%). In two cases, L. innocua was detected in a biofilm. Furthermore, we explored the resident microbial community in the processing environment and on biofilm-positive sites, as well as the co-occurrence of bacterial taxa with Listeria by 16S rRNA gene sequencing. Pseudomonas, Acinetobacter, and Exiguobacterium dominated the microbial community of the processing environment. Using differential abundance analysis, amplicon sequence variants (ASVs) assigned to Enterobacterales (Enterobacter, Serratia, unclassified Enterobacteriaceae) and Carnobacterium were found to be significantly higher abundant in Listeria-positive samples. Several Pseudomonas ASVs were less abundant in Listeria-positive compared to Listeria-negative samples. Acinetobacter, Pseudomonas, Janthinobacterium, Brevundimonas, and Exiguobacterium were key players in the microbial community in biofilms, and Exiguobacterium and Janthinobacterium were more relatively abundant in biofilms. Further, the microbial composition varied between the different areas and the surface materials.

Raw milk cheeses from Beira Baixa, Portugal-A contributive study for the microbiological hygiene and safety assessment

Due to specific bacterial microbiota, raw milk cheeses have appreciated sensory properties. However, they may pose a threat to consumer safety due to potential pathogens presence. This study evaluated the microbiological contamination of 98 raw milk cheeses from Beira Baixa, Portugal. Presence and enumeration of Coagulase Positive Staphylococci (CPS), Listeria monocytogenes, Salmonella spp., pathogenic Escherichia coli, and indicator microorganisms (non-pathogenic E. coli and Listeria spp.) was attained. E. coli antimicrobial resistance (AMR) was also evaluated. PCR and/or Whole genome sequencing (WGS) was used to characterize E. coli, Salmonella spp. and L. monocytogenes isolates. Sixteen cheeses (16.3%) were classified as Satisfactory, 59 (60.2%) as Borderline and 23 (23.5%) as Unsatisfactory/Potential Injurious to Health. L. monocytogenes, CPS > 104 cfu g-1, Extraintestinal pathogenic E. coli (ExPEC) and Salmonella spp. were detected in 4.1%, 6.1%, 3.1% and 1.0% of the samples, respectively. Listeria innocua (4.1%) and E. coli > 104 cfu g-1 (16.3%) were also detected. AMR E. coli was detected in 23/98 (23.5%) of the cheese samples, of which two were multidrug resistant. WGS identified genotypes already associated to human disease and Listeria spp. cluster analysis indicated that cheese contamination might be related with noncompliance with Good Hygiene Practices during cheese production.

Intensive Environmental Sampling and Whole Genome Sequence-based Characterization of Listeria in Small- and Medium-sized Dairy Facilities Reveal Opportunities for Simplified and Size-appropriate Environmental Monitoring Strategies

Small- and medium-sized dairy processing facilities (SMDFs) may face unique challenges with respect to controlling Listeria in their processing environments, e.g., due to limited resources. The aim of this study was to implement and evaluate environmental monitoring programs (EMPs) for Listeria control in eight SMDFs in a ∼1-year longitudinal study; this included a comparison of pre-operation (i.e., after cleaning and sanitation and prior to production) and mid-operation (i.e., at least 4 h into production) sampling strategies. Among 2,072 environmental sponge samples collected across all facilities, 272 (13%) were positive for Listeria. Listeria prevalence among pre- and mid-operation samples (15% and 17%, respectively), was not significantly different. Whole genome sequencing (WGS) performed on select isolates to characterize Listeria persistence patterns revealed repeated isolation of closely related Listeria isolates (i.e., ≤20 high-quality single nucleotide polymorphism [hqSNP] differences) in 5/8 facilities over >6 months, suggesting Listeria persistence and/or reintroduction was relatively common among the SMDFs evaluated here. WGS furthermore showed that for 41 sites where samples collected pre- and mid-operation were positive for Listeria, Listeria isolates obtained were highly related (i.e., ≤10 hqSNP differences), suggesting that pre-operation sampling alone may be sufficient and more effective for detecting sites of Listeria persistence. Importantly, our data also showed that only 1/8 of facilities showed a significant decrease in Listeria prevalence over 1 year, indicating continued challenges with Listeria control in at least some SMDFs. We conclude that options for simplified Listeria EMPs (e.g., with a focus on pre-operation sampling, which allows for more rapid identification of likely persistence sites) may be valuable for improved Listeria control in SMDFs.

Genomic characterization of Listeria monocytogenes and Listeria innocua isolated from milk and dairy samples in Ethiopia

Listeriosis caused by Listeria monocytogenes often poses a significant threat to vulnerable populations. Dairy products have been implicated in outbreaks of listeriosis worldwide. In Ethiopia, studies have identified Listeria spp. and L. monocytogenes in various dairy products, but the genetic diversity and phylogenetic relationships of these bacteria remain largely unknown in the low- and middle-income countries. Therefore, we conducted whole-genome sequencing on 15 L. monocytogenes and 55 L. innocua isolates obtained from different levels of the dairy supply chains across three regions in Ethiopia. Genomes were assembled and used for MLST genotyping and single nucleotide polymorphism (SNP) analysis to infer phylogenetic relationships. We identified a total of 3 L. monocytogenes (i.e., 2, 145, and 18) and 12 L. innocua (i.e., 1489, 1619, 603, 537, 1010, 3186, 492, 3007, 1087, 474, 1008, and 637) MLST sequence types among the studied isolates. Some of these sequence types showed region-specific occurrence, while others were broadly distributed across regions. Through high-quality SNP analysis, we found that among 13 L. monocytogenes identified as ST 2, 11 of them were highly similar with low genetic variation, differing by only 1 to 10 SNPs, suggesting potential selection in the dairy food supply chain. The L. innocua isolates also exhibited low intra-ST genetic variation with only 0-10 SNP differences, except for the ST 1619, which displayed a greater diversity.

Impact of vitamin B12 on rhamnose metabolism, stress defense and in-vitro virulence of Listeria monocytogenes

Listeria monocytogenes is a facultative anaerobe which can cause a severe food-borne infection known as listeriosis. L. monocytogenes is capable of utilizing various nutrient sources including rhamnose, a naturally occurring deoxy sugar abundant in foods. L. monocytogenes can degrade rhamnose into lactate, acetate and 1,2-propanediol. Our previous study showed that addition of vitamin B12 stimulated anaerobic growth of L. monocytogenes on rhamnose due to the activation of bacterial microcompartments for 1,2-propanediol utilization (pdu BMC) with concomitant production of propionate and propanol. Notably, anaerobic 1,2-propanediol metabolism has been linked to virulence of enteric pathogens including Salmonella spp. and L. monocytogenes. In this study we investigated the impact of B12 and BMC activation on i) aerobic and anerobic growth of L. monocytogenes on rhamnose and ii) the level of virulence. We observed B12-induced pdu BMC activation and growth stimulation only in anaerobically grown cells. Comparative Caco-2 virulence assays showed that these pdu BMC-induced cells have significantly higher translocation efficiency compared to non-induced cells (anaerobic growth without B12; aerobic growth with or without B12), while adhesion and invasion capacity is similar for all cells. Comparative proteome analysis showed specific and overlapping responses linked to metabolic shifts, activation of stress defense proteins and virulence factors, with RNA polymerase sigma factor SigL, teichoic acid export ATP-binding protein TagH, DNA repair and protection proteins, RadA and DPS, and glutathione synthase GshAB, previously linked to activation of virulence response in L. monocytogenes, uniquely upregulated in anaerobically rhamnose grown pdu-induced cells. Our results shed light on possible effects of B12 on L. monocytogenes competitive fitness and virulence activation when utilizing rhamnose in anaerobic conditions encountered during transmission and the human intestine.

Persistence of microbiological hazards in food and feed production and processing environments

Listeria monocytogenes (in the meat, fish and seafood, dairy and fruit and vegetable sectors), Salmonella enterica (in the feed, meat, egg and low moisture food sectors) and Cronobacter sakazakii (in the low moisture food sector) were identified as the bacterial food safety hazards most relevant to public health that are associated with persistence in the food and feed processing environment (FFPE). There is a wide range of subtypes of these hazards involved in persistence in the FFPE. While some specific subtypes are more commonly reported as persistent, it is currently not possible to identify universal markers (i.e. genetic determinants) for this trait. Common risk factors for persistence in the FFPE are inadequate zoning and hygiene barriers; lack of hygienic design of equipment and machines; and inadequate cleaning and disinfection. A well-designed environmental sampling and testing programme is the most effective strategy to identify contamination sources and detect potentially persistent hazards. The establishment of hygienic barriers and measures within the food safety management system, during implementation of hazard analysis and critical control points, is key to prevent and/or control bacterial persistence in the FFPE. Once persistence is suspected in a plant, a 'seek-and-destroy' approach is frequently recommended, including intensified monitoring, the introduction of control measures and the continuation of the intensified monitoring. Successful actions triggered by persistence of L. monocytogenes are described, as well as interventions with direct bactericidal activity. These interventions could be efficient if properly validated, correctly applied and verified under industrial conditions. Perspectives are provided for performing a risk assessment for relevant combinations of hazard and food sector to assess the relative public health risk that can be associated with persistence, based on bottom-up and top-down approaches. Knowledge gaps related to bacterial food safety hazards associated with persistence in the FFPE and priorities for future research are provided.

Comparative genomics unveils extensive genomic variation between populations of Listeria species in natural and food-associated environments

Comprehending bacterial genomic variation linked to distinct environments can yield novel insights into mechanisms underlying differential adaptation and transmission of microbes across environments. Gaining such insights is particularly crucial for pathogens as it benefits public health surveillance. However, the understanding of bacterial genomic variation is limited by a scarcity of investigations in genomic variation coupled with different ecological contexts. To address this limitation, we focused on Listeria, an important bacterial genus for food safety that includes the human pathogen L. monocytogenes, and analyzed a large-scale genomic dataset collected by us from natural and food-associated environments across the United States. Through comparative genomics analyses on 449 isolates from the soil and 390 isolates from agricultural water and produce processing facilities representing L. monocytogenes, L. seeligeri, L. innocua, and L. welshimeri, we find that the genomic profiles strongly differ by environments within each species. This is supported by the environment-associated subclades and differential presence of plasmids, stress islands, and accessory genes involved in cell envelope biogenesis and carbohydrate transport and metabolism. Core genomes of Listeria species are also strongly associated with environments and can accurately predict isolation sources at the lineage level in L. monocytogenes using machine learning. We find that the large environment-associated genomic variation in Listeria appears to be jointly driven by soil property, climate, land use, and accompanying bacterial species, chiefly representing Actinobacteria and Proteobacteria. Collectively, our data suggest that populations of Listeria species have genetically adapted to different environments, which may limit their transmission from natural to food-associated environments.

Genomic Characterization of Listeria innocua Isolates Recovered from Cattle Farms, Beef Abattoirs, and Retail Outlets in Gauteng Province, South Africa

Whole-genome sequencing (WGS) was used for the genomic characterization of one hundred and ten strains of Listeria innocua (L. innocua) isolated from twenty-three cattle farms, eight beef abattoirs, and forty-eight retail outlets in Gauteng province, South Africa. In silico multilocus sequence typing (MLST) was used to identify the isolates' sequence types (STs). BLAST-based analyses were used to identify antimicrobial and virulence genes. The study also linked the detection of the genes to the origin (industries and types of samples) of the L. innocua isolates. The study detected 14 STs, 13 resistance genes, and 23 virulence genes. Of the 14 STs detected, ST637 (26.4%), ST448 (20%), 537 (13.6%), and 1085 (12.7%) were predominant, and the frequency varied significantly (p < 0.05). All 110 isolates of L. innocua were carriers of one or more antimicrobial resistance genes, with resistance genes lin (100%), fosX (100%), and tet(M) (30%) being the most frequently detected (p < 0.05). Of the 23 virulence genes recognized, 13 (clpC, clpE, clpP, hbp1, svpA, hbp2, iap/cwhA, lap, lpeA, lplA1, lspA, oatA, pdgA, and prsA2) were found in all 110 isolates of L. innocua. Overall, diversity and significant differences were detected in the frequencies of STs, resistance, and virulence genes according to the origins (source and sample type) of the L. innocua isolates. This, being the first genomic characterization of L. innocua recovered from the three levels/industries (farm, abattoir, and retail) of the beef production system in South Africa, provides data on the organism's distribution and potential food safety implications.

Effects of Selected Essential Oils on Listeria monocytogenes in Biofilms and in a Model Food System

The composition of 18 essential oils was determined using gas chromatography-mass spectrometry, and their antilisterial activity was evaluated by the disk diffusion method, followed by the determination of the minimum inhibitory and minimum bactericidal concentrations. The most active essential oils were oregano, thyme, cinnamon, winter savory, and clove, with MIC values ranging from 0.09 to 1.78 µL/mL. We investigated the biofilm-forming potential of Listeria monocytogenes on polystyrene at 5 °C, 15 °C, and 37 °C in three different media. The formation of biofilm was found to be dependent on the temperature and the availability of nutrients. After treatment with selected essential oils, the reduction in biofilm biomass was in the range of 32.61% and 78.62%. Micromorphological changes in the L. monocytogenes treated by oregano and thyme essential oils were observed in the form of impaired cell integrity and cell lyses by using scanning electron microscope. Oregano and thyme essential oils (MIC and 2MIC) significantly (p < 0.05) reduced the population of L. monocytogenes in minced pork meat during storage at 4 °C. In conclusion, the obtained results indicated the good activity of some selected essential oils on L. monocytogenes, with bacteriostatic, bactericidal, and antibiofilm effects at very low concentrations.

Evaluation of Commercial Anti-Listerial Products for Improvement of Food Safety in Ready-to-Eat Meat and Dairy Products

In ready-to-eat products, such as cooked ham, fresh cheese, and fuet in which Listeria monocytogenes is a concern, the use of biopreservation techniques represents an additional hurdle to inhibit pathogen growth during storage. The objective of this study was to apply several biopreservation techniques in three different food matrices to reduce the growth of Listeria innocua, used as a surrogate of L. monocytogenes. Several lactic acid bacteria, the bacteriocin nisin, the bacteriophage PhageGuard Listex^TM P100, and the enzyme lysozyme were evaluated. Cooked ham treated with the bacteriophage PhageGuard Listex^TM at 0.5% or with the lactic acid bacteria SafePro^® B-SF-43 (25 g/100 kg) reduced L. innocua population to below the detection limit after 7 days of storage (4 °C plus modified atmosphere packaging). In fresh cheese, the application of PhageGuard Listex^TM at 0.2 and 0.5% reduced L. innocua counts by more than 3.4 logarithmic units after 6 days at 4 °C. In fuet, the 1.0% of PhageGuard Listex^TM reduced L. innocua population by 0.7 ± 0.2 logarithmic units in front of control with no significant differences to other evaluated biopreservative agents. The present results confirm that the application of biopreservation techniques was able to inhibit L. innocua in fuet, cooked ham, and fresh cheese, and suggest that the type of food matrix and its physicochemical characteristics influence the biopreservative efficacy.

Tracing of persistent Listeria monocytogenes contamination in ewe's milk farm

Ewe's milk farm production is permanently associated with the risk of contamination by pathogenic bacteria, including Listeria monocytogenes. In the present study, the prevalence and diversity of L. monocytogenes strains repeatedly isolated from tank ewe's milk and the milking environment on a farm in Slovakia during a prolonged period were investigated to identify the source of potentially persistent contamination. A total of 140 samples along the milk production chain were collected during an 18-month period. From all these samples, 45 samples were found L. monocytogenes positive with 90.3% positivity of tank milk samples (28 positive samples from 31 analysed). Pulsed-field gel electrophoresis profiling resulted in strain discrimination into six profiles with one pulsotype (NS1) corresponding to MLST-ST14 being predominant. A total of 17 proportionally selected L. monocytogenes isolates, including 11 NS1/ST14 isolates, were subjected to whole genome sequencing. Resulted data were used to compare the genomes diversity and to confirm the persistent contamination when <10 allelic differences threshold in cgMLST analysis was applied. The source of persistent contamination was localized inside the milking apparatus, probably in shelters that were very difficult to clean. Despite great efforts, the ewe's milk contamination could not be eliminated during the reporting period.

Identification of Listeria species and Multilocus Variable-Number Tandem Repeat Analysis (MLVA) Typing of Listeria innocua and Listeria monocytogenes Isolates from Cattle Farms and Beef and Beef-Based Products from Retail Outlets in Mpumalanga and North West Provinces, South Africa

In this study, Listeria isolates (214) were characterized as follows: L. innocua (77.10%), L. monocytogenes (11.21%), L. welshimeri (5.61%), L. grayi (1.40%), L. seeligeri (0.93%), and L. species (3.73%) that were not identified at the species level, from beef and beef based products from retail and farms in Mpumalanga and North West provinces of South Africa. MLVA was further used to type Listeria innocua isolates (165) and Listeria monocytogenes isolates (24). The L. monocytogenes isolates were also serogrouped using PCR. The MLVA protocol for L. monocytogenes typing included six tandem repeat primer sets, and the MLVA protocol for L. innocua included the use of three tandem repeats primer sets. The L. monocytogenes serogroups were determined as follows: 4b-4d-4e (IVb) (37.50%), 1/2a-3a (IIa) (29.16%), 1/2b-3b (IIb) (12.50%), 1/2c-3c (IIc) (8.33%), and IVb-1 (4.16%). MLVA could cluster isolates belonging to each specie, L. monocytogenes, and L. innocua isolates, into MLVA-related strains. There were 34 and 10 MLVA types obtained from the MLVA typing of L. innocua and L. monocytogenes, respectively. MLVA clustered the L. monocytogenes isolates irrespective of sample category, serogroups, and geographical origin. Similarly, the L. innocua isolates clustered irrespective of meat category and geographical origin. MLVA was able to cluster isolates based on MLVA relatedness. The clustering of isolates from farms and retailers indicates transmission of Listeria spp. MLVA is an affordable, simple, and discriminatory method that can be used routinely to type L. monocytogenes and L. innocua isolates.

Genetic diversity and known virulence genes in Listeria innocua strains isolated from cattle abortions and farm environment

Listeria innocua is considered as non-pathogenic bacteria living in an environment although several cases of immunocompromised humans and ruminant listeriosis infections have been reported. Previously, L. innocua was identified as a potential pathogen and virulence in association with L. monocytogenes PrfA dependent virulence (LIPI-1) gene cluster was demonstrated in hemolytic L. innocua. L. innocua usually considered non-pathogenic versus pathogenic L. monocytogenes and L. ivanovii because of the main virulence gene loss. There are limited studies and reports available about L. innocua-caused illness in cattle. A total of 18 STs were identified in cattle abortions while 17 STs in the farm environment with majority of STs were present in both abortions and environmental samples. Genome sequencing showed that in one farm identical L. innocua clones were represented in water, feed, soil, and faeces sample groups, suggesting that animals most likely through the faecal shedding may remain as the main source of L. innocua in a farm environment. Out of all L. innocua isolates PrfA-dependent virulence genes were not found in aborted foetuses isolates and environmental L. innocua isolate groups; however, in 20% of isolates a complete LIPI-3 pathogenicity island encoding listeriolysin S was identified. In this study, we demonstrated that genetically diverse L. innocua clones were widely distributed in cattle farm environment and certain isolates had a significant pathogenicity potential for cattle, thus causing adverse health effects, including abortions.

Comparison between qPCR, VIDAS immunoassays and agar streaking for the detection of Listeria monocytogenes from food and environmental surfaces containing and not containing Listeria innocua

Comparisons among a qPCR assay, VIDAS® assays and a conventional agar streaking method following the same enrichment for the detection of Listeria monocytogenes were performed under two challenging conditions. In the first comparison, L. innocua and L. monocytogenes were coinoculated into sausages at ratios (L. innocua-to-L. monocytogenes) of 10, 100, 1000, and 10 000. qPCR provided the most sensitive detection at all ratios after both 24-h and 48-h enrichments. A modified VIDAS® LMO2 assay (i.e., replacement of the kit-specified enrichment scheme with the enrichment scheme used in this study) and agar streaking yielded equivalent results when the ratio was 10 and 100; agar streaking was more sensitive when the ratio was 1000; neither method could detect L. monocytogenes at the ratio of 10 000. Enrichment duration of 48 h was needed for modified VIDAS® to detect L. monocytogenes when the ratio was 1000. Agar streaking after 24-h enrichment isolated L. monocytogenes better than after 48-h enrichment when the ratio was 100 and 1000. In the second comparison, we followed the validation guidelines of AOAC International and inoculated L. monocytogenes, without any L. innocua, onto lettuce and stainless-steel surfaces at low levels. The numbers of positive samples detected by qPCR, VIDAS® LIS assay, modified VIDAS® LMO2 assay, and agar streaking after 48-h enrichment were not statistically different. Our data showed that qPCR was the most sensitive method, while agar streaking and VIDAS® performed reasonably well. Streaking after 24-h enrichment was needed when background flora could overgrow L. monocytogenes during prolonged enrichment, and this is critical for confirming rapid screening assays. Appropriate selection of enrichment duration and rapid assays will enhance the testing of L. monocytogenes in food and environmental samples.

Isolation, discrimination, and molecular detection of Listeria species from slaughtered cattle in Namwala District, Zambia

BACKGROUND

The food industry is increasingly becoming more scrutinized, given the frequency and intensity with which zoonotic diseases are being reported. Pathogen tracking has become more applicable with regards food safety. It is in this regard that the present study was formulated to track Listeria species. in freshly slaughtered cattle carcasses by utilizing standard and molecular biological techniques.

METHODS

A cross-sectional study design was conducted from March to December 2020 with 200 samples being equally collected in the rainy and dry seasons. A total of 180 and 20 swabs were aseptically collected from carcasses and the environment respectively. Samples were first subjected to pre-enrichment in half-strength Fraser broth followed by enrichment in full strength Fraser broth and subsequent plating on Listeria agar. Listeria growth characteristics were identified up to species level based on their morphological and biochemical characteristics. Further, molecular detection and phylogenetic analysis was conducted. Quantitative proportionate survey data were analyzed using Stata Version 15 software to estimate crude prevalence taking into account complex design at abattoir level. Factors associated with contamination were characterized using logistic regression. Sequences were analyzed using, Genetyyx version 12 and phylogenetic Mega.

RESULTS

Of the 200 samples, 19 were positive for Listeria species identified as L.innocua 14/19 (73.7%) and L. monocytogenes 5/19 (26.3%). All isolates were from freshly slaughtered carcasses, and none from environment. Siginificant differences in contamination levels were observed based on season: rainy season yielded 14 (73.6%) whilst the dry season 5 (26.3%). The L. monocytogenes strains showed a high degree of homogeneity on phylogenetic analysis and clustered based on abattoir. Seasonality was identified as a major determinant influencing contamination based on the final logistic regression model.

CONCLUSION

This study found evidence of L. monocytogenes contamination on traditionally raised beef carcasses across various abattoirs surveyed. The failure to find Listeria contamination on the abattoir environment may to a greater extent intimate cattle carccases as primary sources of contamination. However, a more comprerehnsive study incorporating different geographical regions is needed to conclusively ascertain these present findings.

Antibiotic Resistance Patterns of Listeria Species Isolated from Broiler Abattoirs in Lusaka, Zambia

L. monocytogenes is a public health threat linked to fast foods such as broiler chickens. This study aimed to verify the occurrence of Listeria species in chickens from abattoirs and evaluate their antimicrobial resistance. In total, 150 broiler carcass swabs distributed as cloacal (n = 60), exterior surface (n = 60), and environmental (n = 30) were collected. Listeria species were characterized using biochemical tests and PCR. We conducted antibiotic resistance tests using the disc diffusion and Etest (Biomerieux, Durham, NC, USA) methods. Overall isolation of Listeria species was 15% (23/150) 95% CI (10.16–22.33), 2% (3/150) 95% CI (0.52–6.19) and 13% (20/150) 95% CI (8.53–20.08) came from environmental swabs and carcass swabs, respectively. Proportions of positive Listeria isolates were L. monocytogenes 74% (17/23), L. welshimeri 22% (5/23), and L. innocua 4% (1/23). Listeria species from the exterior carcass swabs was 61% (14/23), cloacal swabs 26% (6/23), and environmental swabs 3% (3/23). L. monocytogenes had the greatest resistance percentage to the following antibiotics: clindamycin (61%, 10/23), tetracycline 30% (7/23), and erythromycin 13%, (3/23). Isolation of L. monocytogenes in relatively high numbers, including the antimicrobial profiles, suggests a potential risk of the pathogen remaining viable in the food continuum and a public health risk to would-be consumers.

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 Special Issue: Transmission and Detection of Food and Environmental Pathogens

To progress towards a full comprehension of the risk caused by pathogenic microorganisms transmitted via food and environmental routes, extensive information on the prevalence, the mechanisms of contamination, and the survival of pathogens is required, particularly to assist with the development of effective systems to reduce contamination, and to formulate procedural control measures, such as the implementation of food safety criteria [...].

Monitoring by a Sensitive Liquid-Based Sampling Strategy Reveals a Considerable Reduction of Listeria monocytogenes in Smeared Cheese Production over 10 Years of Testing in Austria

Most Austrian dairies and cheese manufacturers participated in a Listeria monitoring program, which was established after the first reports of dairy product-associated listeriosis outbreaks more than thirty years ago. Within the Listeria monitoring program, up to 800 mL of product-associated liquids such as cheese smear or brine are processed in a semi-quantitative approach to increase epidemiological sensitivity. A sampling strategy within cheese production, which detects environmental contamination before it results in problematic food contamination, has benefits for food safety management. The liquid-based sampling strategy was implemented by both industrial cheese makers and small-scale dairies located in the mountainous region of Western Austria. This report considers more than 12,000 Listeria spp. examinations of liquid-based samples in the 2009 to 2018 timeframe. Overall, the occurrence of L. monocytogenes in smear liquid samples was 1.29% and 1.55% (n = 5043 and n = 7194 tested samples) for small and industrial cheese enterprises, respectively. The liquid-based sampling strategy for Listeria monitoring at the plant level appears to be superior to solid surface monitoring. Cheese smear liquids seem to have good utility as an index of the contamination of cheese up to that point in production. A modelling or validation process should be performed for the new semi-quantitative approach to estimate the true impact of the method in terms of reducing Listeria contamination at the cheese plant level.

Co-Occurrence of Listeria spp. and Spoilage Associated Microbiota During Meat Processing Due to Cross-Contamination Events

A large part of foodborne outbreaks related to Listeria monocytogenes are linked to meat and meat products. Especially, recontamination of meat products and deli-meat during slicing, packaging, and repackaging is in the focus of food authorities. In that regard, L. monocytogenes persistence in multi-species biofilms is one major issue, since they survive elaborate cleaning and disinfection measures. Here, we analyzed the microbial community structure throughout a meat processing facility using a combination of high-throughput full-length 16S ribosomal RNA (rRNA) gene sequencing and traditional microbiological methods. Samples were taken at different stages during meat cutting as well as from multiple sites throughout the facility environment to capture the product and the environmental associated microbiota co-occurring with Listeria spp. and L. monocytogenes. The listeria testing revealed a widely disseminated contamination (50%; 88 of 176 samples were positive for Listeria spp. and 13.6%; 24 of 176 samples were positive for L. monocytogenes). The pulsed-field gel electrophoresis (PFGE) typing evidenced 14 heterogeneous L. monocytogenes profiles with PCR-serogroup 1/2a, 3a as most dominant. PFGE type MA3-17 contributed to the resilient microbiota of the facility environment and was related to environmental persistence. The core in-house microbiota consisted mainly of the genera Acinetobacter, Pseudomonas, Psychrobacter (Proteobacteria), Anaerobacillus, Bacillus (Firmicutes), and Chryseobacterium (Bacteroidota). While the overall microbial community structure clearly differed between product and environmental samples, we were able to discern correlation patterns regarding the presence/absence of Listeria spp. in both sample groups. Specifically, our longitudinal analysis revealed association of Listeria spp. with known biofilm-producing Pseudomonas, Acinetobacter, and Janthinobacterium species on the meat samples. Similar patterns were also observed on the surface, indicating dispersal of microorganisms from this multispecies biofilm. Our data provided a better understanding of the built environment microbiome in the meat processing context and promoted more effective options for targeted disinfection in the analyzed facility.

Sampling the Food-Processing Environment: Taking Up the Cudgel for Preventive Quality Management in Food Processing (FP)

The Listeria monitoring program for Austrian dairies and cheese factories was established in 1988. The aim was to control the entrance of L. monocytogenes into the food-processing environment (FPE), preventing the contamination of food under processing. The Austrian Listeria monitoring program comprises four levels of investigation, dealing with routine monitoring of samples and consequences of finding a positive sample. Preventive quality control concepts attempt to detect a foodborne hazard along the food-processing chain, prior to food delivery, retailing, and consumption. The implementation of a preventive food safety concept provokes a deepened insight by the manufacturers into problems concerning food safety. The development of preventive quality assurance strategies contributes to the national food safety status and protects public health.