Important vectors for Listeria monocytogenes transmission at farm dairies manufacturing fresh sheep and goat cheese from raw milk

High multidrug resistance of Listeria monocytogenes and association with water sources in sheep and goat dairy flocks in Jordan

Listeria monocytogenes is a significant pathogen that causes listeriosis in humans and small ruminants. This study aimed to estimate the prevalence, antimicrobial resistance and risk factors of L. monocytogenes in small dairy ruminants in Jordan. A total of 948 milk samples were collected from 155 sheep and goat flocks across Jordan. L. monocytogenes was isolated from the samples, confirmed and tested for 13 clinically important antimicrobials. Data were also collected on the husbandry practices to identify risk factors for the presence of L. monocytogenes. The results showed that the flock-level prevalence of L. monocytogenes was 20.0% (95% CI; 14.46%-26.99%) and the prevalence in the individual milk samples was 6.43% (95% CI; 4.92%-8.36%). The univariable (UOR=2.65, p = 0.021) and multivariable (AOR=2.49, p = 0.028) analyses showed that using water from municipality pipelines as a water source in the flock reduced L. monocytogenes prevalence. All L. monocytogenes isolates were resistant to at least one antimicrobial. High percentages of the isolates were resistant to ampicillin (83.6%), streptomycin (79.3%), kanamycin (75.0%), quinupristin/dalfopristin (63.8%) and clindamycin (61.2%). About 83.6% of the isolates (94.2% and 75% of the sheep and goat isolates) exhibited multidrug resistance (resistance to ≥3 antimicrobial classes). In addition, the isolates exhibited fifty unique antimicrobial resistance profiles. Thus, it's recommended to restrict the misuse of clinically important antimicrobials and to chlorinate and monitor the water sources in sheep and goat flocks.

Transmission Scenarios of Listeria monocytogenes on Small Ruminant On-Farm Dairies

Listeria monocytogenes can cause severe foodborne infections in humans and invasive diseases in different animal species, especially in small ruminants. Infection of sheep and goats can occur via contaminated feed or through the teat canal. Both infection pathways result in direct (e.g., raw milk from an infected udder or fresh cheese produced from such milk) or indirect exposure of consumers. The majority of dairy farmers produces a high-risk product, namely fresh cheese made from raw ewe's and goat's milk. This, and the fact that L. monocytogenes has an extraordinary viability, poses a significant challenge to on-farm dairies. Yet, surprisingly, almost no scientific studies have been conducted dealing with the hygiene and food safety aspects of directly marketed dairy products. L. monocytogenes prevalence studies on small ruminant on-farm dairies are especially limited. Therefore, it was our aim to focus on three main transmission scenarios of this important major foodborne pathogen: (i) the impact of caprine and ovine listerial mastitis; (ii) the significance of clinical listeriosis and outbreak scenarios; and (iii) the impact of farm management and feeding practices.

Asymptomatic Carriage of Listeria monocytogenes by Animals and Humans and Its Impact on the Food Chain

Humans and animals can become asymptomatic carriers of Listeria monocytogenes and introduce the pathogen into their environment with their feces. In turn, this environmental contamination can become the source of food- and feed-borne illnesses in humans and animals, with the food production chain representing a continuum between the farm environment and human populations that are susceptible to listeriosis. Here, we update a review from 2012 and summarize the current knowledge on the asymptomatic carrier statuses in humans and animals. The data on fecal shedding by species with an impact on the food chain are summarized, and the ways by which asymptomatic carriers contribute to the risk of listeriosis in humans and animals are reviewed.

Molecular characterization and hematological analysis of Listeria monocytogenes infection in dairy cows in Punjab (Pakistan)

Listeriosis is an emerging bacterial disease of animals and humans worldwide, caused by Listeria monocytogenes. The infected dairy cows continuously shed the microbes in their milk, a human being's concern. This study was designed to molecular characterize the Listeria monocytogenes isolated from symptomatic cow's milk of tehsils Samundri, Gujar khan, and Alipur of Punjab. A total of 175 milk samples were collected, pre-enriched and cultured on PALCAM agar. The affirmation of the hlyA gene of Listeria monocytogenes was performed by polymerase chain reaction (PCR) and 3.43% of isolates were found positive. The phylogenetic analysis showed a resemblance of our isolates of Listeria monocytogenes with India (KP965733), the USA (DQ812484), and 3 of our isolates made a clade. The leucocytes and neutrophils count were found significantly increased in listeriosis affected cows. The Chi-square test showed a significant association between poor quality silage feeding and listeriosis. The presence of L.monocytogenes in cow's milk indicates a potential threat to humans. It is further recommended that it should be consistently monitored to ensure food safety.

A model to predict the fate of Listeria monocytogenes in different cheese types - A major role for undissociated lactic acid in addition to pH, water activity, and temperature

Undissociated lactic acid has been shown to play a major role in complete growth inhibition of Listeria monocytogenes in Gouda cheese. In addition, low water activity conditions may contribute to growth inhibition. In the current study, it was assessed whether the major factors that inhibit growth of L. monocytogenes in Gouda cheese are the factors that determine growth in other types of ready-to-eat cheese as well. Various types of cheeses were selected, some of which had been associated with listeriosis, while others had not. Based on the composition of the different cheese types, the concentrations of undissociated lactic acid were calculated for each type. The ability to support growth of L. monocytogenes was predicted using the Gamma model, based on literature data on total lactic acid content, moisture content, fat content, pH, Aw, and temperature, and optimal growth rates in milk at 30-37 °C. In addition, the actual specific growth rates of L. monocytogenes in the various cheeses were calculated based on available experimental growth data. In 9 out of the 10 RTE cheeses reviewed, the undissociated lactic acid concentrations and a_w determined growth/no growth of L. monocytogenes. No growth was correctly predicted for feta, Cheddar and Gouda, and growth was correctly predicted for ricotta, queso fresco, Camembert, high-moisture mozzarella, cottage and blue cheese. Growth of L. monocytogenes was not observed in practice upon inoculation of Emmental, whereas growth in this cheese type was predicted when including the above mentioned factors in the models. Other factors, presumably acetic and propionic acid, are thought to be important to inhibit growth of the pathogen in Emmental. The results from our study show that for cheeses in which lactic acid is a main acid, our model based on undissociated lactic acid, temperature, pH and a_w gives a good prediction of potential outgrowth of L. monocytogenes. Implications for L. monocytogenes legislation are discussed per type of RTE cheese reviewed.

Characterization and Genetic Diversity of Listeria monocytogenes Isolated from Cattle Abortions in Latvia, 2013-2018

Listeria monocytogenes can cause disease in humans and in a wide range of animal species, especially in farm ruminants. The aim of the study was to determine the prevalence and genetic diversity of L. monocytogenes related to 1185 cattle abortion cases in Latvia during 2013-2018. The prevalence of L. monocytogenes among cattle abortions was 16.1% (191/1185). The seasonality of L. monocytogenes abortions was observed with significantly higher occurrence (p < 0.01) in spring (March-May). In 61.0% of the cases, the affected cattle were under four years of age. L. monocytogenes abortions were observed during the third (64.6%) and second (33.3%) trimesters of gestation. Overall, 27 different sequence types (ST) were detected, and four of them, ST29 (clonal complex, CC29), ST37 (CC37), ST451 (CC11) and ST7 (CC7), covered more than half of the L. monocytogenes isolates. Key virulence factors like the prfA-dependent virulence cluster and inlA, inlB were observed in all the analyzed isolates, but lntA, inlF, inlJ, vip were associated with individual sequence types. Our results confirmed that L. monocytogenes is the most important causative agent of cattle abortions in Latvia and more than 20 different STs were observed in L. monocytogenes abortions in cattle.

Application and Future Prospective of Lactic Acid Bacteria as Natural Additives for Silage Production—A Review

Ensiling is one of the essential processes to preserve fodder with high nutrients and microbiological quality. The forages before ensiling have a limited number of bacteria associated with the controlled fermentation process. Undesirable microbes can grow in silages when there is not efficient fermentation. Such kinds of microbes might cause pathogenic or toxic compounds that affect animal and human health. Therefore, it is necessary to inoculate potent starter cultures. Lactic acid bacteria’s (LABs) have been considered the most prominent microbial additives used to improve the quality of silage. Currently, LABs have been used in modern and sustainable agriculture systems due to their biological potential. Recently, many scientists have increased their focus on developing nutrient-rich animal feed from forages with LAB. This current review focuses on issues related to forage preservation in the form of silages, how undesirable microbes affect the fermentation process, the critical role of LAB in silage production, and the selection of potent LABs to effectively control unwanted microbial growth and promote those which favor animal growth.

Multiresistant zoonotic pathogens isolated from goat milk in Northeastern Brazil

Dairy goats play a significant role in socio-economic, cultural, and nutritional development in many countries. This study aimed to identify multiresistant zoonotic pathogens causing mastitis in goats, in addition to characterizing them for the presence of resistance genes and phenotypic resistance. A total of 714 milk samples from 357 lactating goats in 12 farms in the Northeast region of Brazil were analyzed. The isolates were submitted to Matrix Associated Laser Desorption-Ionization - Time of Flight to identify bacterial species, Polymerase Chain Reaction (PCR) to search for resistance genes, and an antibiogram to evaluate the phenotypic profile of antimicrobial resistance. A total of 214 pathogens were identified and bacterial prevalence was 83.29 % (178/214) Staphylococcus spp.; 6.50 % (14/214) Micrococcus luteus; 3.73 % (8/214) Corynebacterium spp.; 2.80 % (6/214) Bacillus spp.; 1.38 % (3/214) Escherichia coli; 0.92 % (2/214) Enterobacter cloacae; 0.46 % (1/214) Aerococcus viridans; 0.46 % (1/214) Morganella morganii; and 0.46 % (1/214) Turicella otitidis. As for gene frequency, 64.60 % (115/178) of the isolates carried the blaZ gene; 37.07 % (66/178) norA; 22.47 % (40/178) tet(L); 16.85 % (30/178) tet(M); 14.04 % (25/178) norB; 8.42 % (15/178) vanA; 7.30 % (13/178) msrA; 6.41 % (5/178) tet-38; 4.49 % (8/178) norC; 2.25 % (4/178) mecA; and 0.56 % (1/178) vanB. Emerging multiresistant zoonotic pathogens are present in the goat milk production chain, especially the coagulase-negative Staphylococcus species that pose a risk to human and animal health.

Zoonotic risks of pathogens from sheep and their milk borne transmission

Sheep were domesticated around 9000 BC in the Middle East, and since then milk from sheep gradually became very popular, not only for drinking but also for making cheeses and other dairy products. Nowadays, these dairy products are also important for people with an allergy to cow milk, and these products are an essential part of the local daily diet in regions of the world that are not suitable for cows and goats. Consumption of raw milk and raw milk products has a zoonotic risk, and with regard to sheep, the main pathogens associated with such dairy products are: Brucella melitensis, Campylobacter spp., Listeria spp., Salmonella spp., Shiga-toxin producing Escherichia coli, Staphylococcus aureus, tick borne encephalitis virus, and Toxoplasma gondii. Especially, young children, elderly people, pregnant women and immunocompromised (YOPI) persons, and those suffering from disease should be aware of the risk of consuming raw milk and raw milk products. This latter risk can be reduced by proper flock health management, prevention of contamination during milking, adequate milk processing, transport, and refrigerated storage. Only processes equaling pasteurization sufficiently reduce zoonotic risks from milk and milk products, but proper cooling is essential and recontamination must be prevented. Therefore, strict hygiene practices throughout the production process and supply chain especially for raw milk and raw dairy products, should be applied. Small scale production systems pose a greater risk compared to industrialized production systems because of a less protocolized and controlled production process. This manuscript describes zoonotic risks of pathogens from sheep and their milk borne transmission. Additionally, routes of contamination, possibilities for multiplication, and prevention measures thereof are described. We summarize some major human outbreaks caused by consumption of sheep milk and products made thereof, and finally discuss their implications.

Retrospective Study of Listeria Monocytogenes Isolated in the Territory of Inner Eurasia from 1947 to 1999

Listeriosis is one of the most significant humans and animals foodborne infectious diseases. Here, we characterized 48 Listeria monocytogenes strains isolated in the territory of inner Eurasia during the second half of the 20th century. A total of 23 strains (52.3%) were susceptible to the nine antibiotics tested, 30.43%, 15.22%, and 8.7% were resistant penicillin G, ampicillin, and enrofloxacin, respectively. We applied the multilocus sequence typing (MLST) scheme to determine the phylogenetic positions of the strains. All but one strain belonged to the II phylogenetic lineage, and the majority of the strains belonged to one of the previously described clonal complexes (СCs). More than 60% of the strains belonged to the clonal complex CC7 that prevailed among all sources, including cattle (58%), small ruminants (64%), rodents (71%), and humans (50%). Further, CC7, CC101, and CC124 were found among human isolates. The MLST scheme was supplemented with virulence gene analysis. In total, eight inlA, six inlB, and six inlC allelic variants were found, and all but one strain carried one of the two inlE alleles. Most strains (62.5%) belonged to the same multivirulence locus sequence typing (MvLST) type, which includes CC7, inlA allele 4, inlB allele 14, inlC allele 6, and inlE allele 8.

Prevalence, molecular characterization, and antimicrobial resistance profiles of Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 on dairy cattle farms in Jordan

This study determined the prevalence, pulsed-field gel electrophoresis profiles, and antimicrobial resistance profile of Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 isolates from dairy cattle farms in Jordan. Samples from bulk tank milk (n = 305), cattle feces (n = 610), and rectoanal mucosal swabs (n = 610) were collected from 61 dairy cattle farms. We confirmed 32 L. monocytogenes, 28 S. enterica, and 24 E. coli O157:H7 isolates from the samples. The farm-level prevalence (at least 1 positive sample per farm) of L. monocytogenes, S. enterica, and E. coli O157:H7 was 27.9, 19.7, and 23.0%, respectively. The prevalence of L. monocytogenes, S. enterica, and E. coli O157:H7 in bulk tank milk was 7.5, 1.6, and 3.3%, respectively. The prevalence of L. monocytogenes and S. enterica in fecal samples was 1.5 and 3.8%, respectively, and the prevalence of E. coli O157:H7 in rectoanal mucosal swabs was 2.3%. Based on disk diffusion testing, all L. monocytogenes, S. enterica, and E. coli O157:H7 isolates exhibited resistance to at least 1 antimicrobial class. Multidrug resistance (resistance to 3 or more classes of antimicrobials) was exhibited by 96.9% of L. monocytogenes, 91.7% of E. coli O157:H7, and 82.1% of S. enterica isolates. Moreover, 93.8, 79.2, and 57.1% of the L. monocytogenes, E. coli O157:H7, and S. enterica isolates, respectively, were resistant to 5 or more antimicrobial classes. More than 50% of L. monocytogenes isolates were resistant to ampicillin, clindamycin, penicillin, erythromycin, quinupristin-dalfopristin, streptomycin, teicoplanin, linezolid, vancomycin, kanamycin, and tetracycline. More than 50% of S. enterica and E. coli O157:H7 isolates were resistant to ampicillin, cephalothin, nalidixic acid, kanamycin, streptomycin, amoxicillin-clavulanic acid, and tetracycline. The prevalence of the studied pathogens this study was comparable to reports from other countries. The isolated pathogens exhibited a high degree of antimicrobial resistance, suggesting that the bacterial flora of dairy cattle in Jordan are under intense antimicrobial selection pressure. Additional research is required to determine the causes and drivers of resistance, and to develop approaches to mitigating antimicrobial resistance.

Chronic intramammary infection by Listeria monocytogenes in a clinically healthy goat - a case report

BACKGROUND

Listeria monocytogenes is a ubiquitous Gram-positive bacterium responsible for a severe foodborne disease in humans, and contaminated dairy products can be an important source of infection. Typically, infected dairy ruminants show clinical manifestations including encephalitis, septicemia, abortion, and diarrhea, but may also become asymptomatic carriers and shed L. monocytogenes in the feces acting as an important source of viable bacteria. Isolation from individual goat milk has been documented very rarely, and chronic, asymptomatic intramammary infection by L. monocytogenes with continuous milk shedding of viable bacteria has never been described in this dairy species.

CASE PRESENTATION

At the routine controls, cheese and bulk milk were positive for L. monocytogenes in a herd of 200 lactating Alpine goats, but none showed clinical signs of listeriosis. Individual milk was subjected to bacterial culture and a clinically healthy goat was identified as affected by a chronic intramammary infection (IMI) by L. monocytogenes. The goat had never shown clinical signs of mastitis or other diseases. Her right half-udder milk was positive to L. monocytogenes in two consecutive samples collected one week apart, as demonstrated by bacterial culture and molecular analysis. Mammary tissues collected after culling were also positive to L. monocytogenes by culture. Histological examination highlighted a chronic interstitial mastitis with leukocyte infiltration, atrophy of the alveoli and presence of corpora amylacea. Immunohistochemistry (IHC) and immunofluorescence (IF) confirmed the presence of high numbers of bacteria in the lumen of mammary alveoli, with intracellular bacteria mainly located in macrophages, but also present in neutrophils and epithelial cells. After culling of the positive goat, bulk tank milk tested negative to L. monocytogenes at the following controls.

CONCLUSION

This study demonstrates that L. monocytogenes can establish a chronic, subclinical IMI in goats with high numbers of bacteria shed in milk, representing a source of contamination for the herd and its dairy products. This underscores the importance of frequently monitoring all dairy herds that sell directly milk and/or fresh cheese and indicates that a chronic L. monocytogenes IMI should also be considered as source of bacteria when bulk tank milk contamination is detected in a dairy goat farm.

Listeria monocytogenes in Milk: Occurrence and Recent Advances in Methods for Inactivation

Milk is one of the most important food items consumed by humans worldwide. In addition to its nutritional importance, milk is an excellent culture medium for microorganisms, which may include pathogens such as Listeria monocytogenes (L. monocytogenes). Traditional processing of milk for direct consumption is based on thermal treatments that efficiently eliminate pathogens, including pasteurization or sterilization. However, the occurrence of L. monocytogenes in milk as a consequence of failures in the pasteurization process or postpasteurization contamination is still a matter of concern. In recent years, consumer demand for minimally processed milk has increased due to the perception of better sensory and nutritional qualities of the products. This review deals with the occurrence of L. monocytogenes in milk in the last 10 years, including regulatory aspects, and recent advances in technologies for the inactivation of this pathogen in milk. The results from studies on nonthermal technologies, such as high hydrostatic pressure, pulsed electric fields, ultrasounds, and ultraviolet irradiation, are discussed, considering their potential application in milk processing plants.

Risk Assessment of Human Listeriosis from Semisoft Cheeses Made from Raw Sheep's Milk in Lazio and Tuscany (Italy)

Semisoft cheese made from raw sheep's milk is traditionally and economically important in southern Europe. However, raw milk cheese is also a known vehicle of human listeriosis and contamination of sheep cheese with Listeria monocytogenes has been reported. In the present study, we have developed and applied a quantitative risk assessment model, based on available evidence and challenge testing, to estimate risk of invasive listeriosis due to consumption of an artisanal sheep cheese made with raw milk collected from a single flock in central Italy. In the model, contamination of milk may originate from the farm environment or from mastitic animals, with potential growth of the pathogen in bulk milk and during cheese ripening. Based on the 48-day challenge test of a local semisoft raw sheep's milk cheese we found limited growth only during the initial phase of ripening (24 hours) and no growth or limited decline during the following ripening period. In our simulation, in the baseline scenario, 2.2% of cheese servings are estimated to have at least 1 colony forming unit (CFU) per gram. Of these, 15.1% would be above the current E.U. limit of 100 CFU/g (5.2% would exceed 1,000 CFU/g). Risk of invasive listeriosis per random serving is estimated in the 10^-12 range (mean) for healthy adults, and in the 10^-10 range (mean) for vulnerable populations. When small flocks (10-36 animals) are combined with the presence of a sheep with undetected subclinical mastitis, risk of listeriosis increases and such flocks may represent a public health risk.

Metagenomic Analysis of Silage

Metagenomics is defined as the direct analysis of deoxyribonucleic acid (DNA) purified from environmental samples and enables taxonomic identification of the microbial communities present within them. Two main metagenomic approaches exist; sequencing the 16S rRNA gene coding region, which exhibits sufficient variation between taxa for identification, and shotgun sequencing, in which genomes of the organisms that are present in the sample are analyzed and ascribed to "operational taxonomic units"; species, genera or families depending on the extent of sequencing coverage. In this study, shotgun sequencing was used to analyze the microbial community present in cattle silage and, coupled with a range of bioinformatics tools to quality check and filter the DNA sequence reads, perform taxonomic classification of the microbial populations present within the sampled silage, and achieve functional annotation of the sequences. These methods were employed to identify potentially harmful bacteria that existed within the silage, an indication of silage spoilage. If spoiled silage is not remediated, then upon ingestion it could be potentially fatal to the livestock.

Routes of Transmission in the Food Chain

More than 250 different foodborne diseases have been described to date, annually affecting about one-third of the world's population. The incidence of foodborne diseases has been underreported and underestimated, and the asymptomatic presentation of some of the illnesses, worldwide heterogeneities in reporting, and the alternative transmission routes of certain pathogens are among the factors that contribute to this. Globalization, centralization of the food supply, transportation of food products progressively farther from their places of origin, and the multitude of steps where contamination may occur have made it increasingly challenging to investigate foodborne and waterborne outbreaks. Certain foodborne pathogens may be transmitted directly from animals to humans, while others are transmitted through vectors, such as insects, or through food handlers, contaminated food products or food-processing surfaces, or transfer from sponges, cloths, or utensils. Additionally, the airborne route may contribute to the transmission of certain foodborne pathogens. Complicating epidemiological investigations, multiple transmission routes have been described for some foodborne pathogens. Two types of transmission barriers, primary and secondary, have been described for foodborne pathogens, each of them providing opportunities for preventing and controlling outbreaks. Primary barriers, the most effective sites of prophylactic intervention, prevent pathogen entry into the environment, while secondary barriers prevent the multiplication and dissemination of pathogens that have already entered the environment. Understanding pathogen dynamics, monitoring transmission, and implementing preventive measures are complicated by the phenomenon of superspreading, which refers to the concept that, at the level of populations, a minority of hosts is responsible for the majority of transmission events.

Prevalence and Genetic Characteristics of Meatborne Listeria monocytogenes Isolates from Livestock Farms in Korea

This study aimed to evaluate the prevalence of Listeria monocytogenes on livestock farms in Korea and determine their serotypes and genetic correlations. Twenty-five livestock farms in Korea (central: 15, south west: 7, south east: 3) were visited 2-3 times, and 2,018 samples (feces: 677, soil: 680, silage: 647, sludge: 14) were collected. Samples were enriched in LEB (Listeria enrichment broth) and Fraser broth media, and then plated on Palcam agar. The isolates were identified by PCR and 16S rRNA gene sequencing. Then, the serotypes, presence of virulence genes (actA, inlA, inlB, plcB, and hlyA), and antibiotic resistance were determined. Genetic correlations among the isolates were evaluated by analyzing the restriction digest pattern with AscI. Of the 2,018 samples, only 3 (0.15%) soil samples (FI-1-FI-3) from 1 farm in the south east region were positive for L. monocytogenes. Based on biochemical tests and multiplex PCR, the serotype of the isolates were 4ab (FI-1 and FI-3) and 3a (FI-2), which are not common in foodborne L. monocytogenes. The 3a serotype isolate was positive for all tested virulence genes, whereas the 4ab serotype isolates were only positive for hlyA, actA, and inlA. The isolates were resistant to all 12 tested antibiotics, especially FI-3. The genetic correlations among the isolates were 100% for those of the same serotype and 26.3% for those of different serotypes. These results indicate that the prevalence of L. monocytogenes on livestock farms in Korea is low; however, the isolates are pathogenic and antibiotic resistant.

Outbreak investigation identifies a single Listeria monocytogenes strain in sheep with different clinical manifestations, soil and water

Listeria (L.) monocytogenes causes orally acquired infections and is of major importance in ruminants. Little is known about L. monocytogenes transmission between farm environment and ruminants. In order to determine potential sources of infection, we investigated the distribution of L. monocytogenes genetic subtypes in a sheep farm during a listeriosis outbreak by applying four subtyping methods (MALDI-TOF-MS, MLST, MLVA and PFGE). L. monocytogenes was isolated from a lamb with septicemia and from the brainstem of three sheep with encephalitis. Samples from the farm environment were screened for the presence of L. monocytogenes during the listeriosis outbreak, four weeks and eight months after. L. monocytogenes was found only in soil and water tank swabs during the outbreak. Four weeks later, following thorough cleaning of the barn, as well as eight months later, L. monocytogenes was absent in environmental samples. All environmental and clinical L. monocytogenes isolates were found to be the same strain. Our results show that the outbreak involving two different clinical syndromes was caused by a single L. monocytogenes strain and that soil and water tanks were potential infection sources during this outbreak. However, silage cannot be completely ruled out as the bales fed prior to the outbreak were not available for analysis. Faeces samples were negative, suggesting that sheep did not act as amplification hosts contributing to environmental contamination. In conclusion, farm management appears to be a crucial factor for the limitation of a listeriosis outbreak.

Absence of growth ofListeria monocytogenesin naturally contaminated Cheddar cheese

Each cheese producer is responsible by the legislation for the number ofListeria monocytogenesin cheese and is required to prove that numbers will not exceed 100 cfu/g throughout the shelf-life of the cheese. Even in the case of hard-cheese such as Cheddar cheese, the absence of growth ofList. monocytogenesduring ripening has to be demonstrated to comply with EU legislation. Studies dedicated to assessingList. monocytogenesgrowth throughout cheese shelf-life are generally based on artificially contaminated cheeses. Contrary to the majority of works, the current study focused on the growth ofList. monocytogenesin naturally contaminated raw milk farmhouse Cheddar cheeses during a five-month ripening period.List. monocytogenesgrowth was assessed by direct count and its presence was detected by enrichment in two naturally contaminated cheese batches. In order to track routes of contamination, 199 processing environment samples from inside and outside the processing facility were taken, and their analysis for the presence ofList. monocytogeneswas performed on four occasions over a 9-month period.List. monocytogenesisolates were differentiated using PFGE and serotyping.List. monocytogenesnever exceeded 20 cfu/g in the cheeses and could not be detected after five months of ripening. Eleven pulsotypes were identified. One pulsotype was found in the yard outside the processing facility, in a vat, on the processing area floor and in a cheese. This indicated that the outside environment constitutes a potential source of contamination of the processing environment and of the cheese. These results demonstrate that this farmhouse Cheddar cheese does not supportList. monocytogenesgrowth and suggests that the efforts to reduce processing environment contamination are worthwhile.

Exendin-4 improves resistance to Listeria monocytogenes infection in diabetic db/db mice

The incidence of diabetes mellitus is increasing among companion animals. This disease has similar characteristics in both humans and animals. Diabetes is frequently identified as an independent risk factor for infections associated with increased mortality. In the present study, homozygous diabetic (db/db) mice were infected with Listeria (L.) monocytogenes and then treated with the anti-diabetic drug exendin-4, a glucagon-like peptide 1 analogue. In aged db/db mice, decreased CD11b(+) macrophage populations with higher lipid content and lower phagocytic activity were observed. Exendin-4 lowered high lipid levels and enhanced phagocytosis in macrophages from db/db mice infected with L. monocytogenes. Exendin-4 also ameliorated obesity and hyperglycemia, and improved ex vivo bacteria clearance by macrophages in the animals. Liver histology examined during L. monocytogenes infection indicated that abscess formation was much milder in exendin-4-treated db/db mice than in the control animals. Moreover, mechanistic studies demonstrated that expression of ATP binding cassette transporter 1, a sterol transporter, was higher in macrophages isolated from the exendin-4-treated db/db mice. Overall, our results suggest that exendin-4 decreases the risk of infection in diabetic animals by modifying the interaction between intracellular lipids and phagocytic macrophages.

A case of bovine raw milk contamination with Listeria monocytogenes

During routine sampling of bulk raw milk on a dairy farm, the pathogenic bacteria Listeria monocytogenes was found to be a contaminant, at numbers < 100 cfu/ml. A strain with an indistinguishable pulsed-field gel electrophoresis pattern was isolated from the bulk milk two months later. Environmental swabs taken at the dairy environment were negative for the presence of L. monocytogenes, indicating a possible case of excretion of the L. monocytogenes directly into the milk. Milk samples were collected from the individual cows and analysed, resulting in the identification of L. monocytogenes excretion (at 280 cfu/ml) from one of the 4 mammary quarters of one dairy cow out of 180. When the infected cow was isolated from the herd, no L. monocytogenes was detected from the remaining herd. The pulsed-field gel electrophoresis pattern of the strain from the individual cow was indistinguishable from that originally isolated from the bulk milk. The infected cow did not show any clinical signs of disease, nor did the appearance of the milk have any physical abnormalities. Antibiotic treatment of the infected mammary quarter was found to be ineffective. This study shows that there can be risks associated with direct contamination of raw milk with L. monocytogenes.