Listeria monocytogenes is a Gram positive, aerobic, facultative anaerobic and nonacid fast bacterium, which can cause the disease listeriosis in both human and animals. It is widely distributed thoroughout the environment and has been isolated from various plant and animal food products associated with listeriosis outbreaks.

Contaminated ready-to-eat food products such as gravad and cold-smoked salmon and rainbow trout have been associated with human listeriosis in Sweden. The aim of this study was to analyse the occurrence and level of L. monocytogenes in
gravad and cold-smoked salmon (Salmo salar) products packed under vacuum or modified atmosphere from retail outlets in Sweden. Isolated strains were characterized by serotyping and the diversity of the strains within and between
producers were determined with PFGE (Pulsed-field gel electrophoresis). The characterized fish isolates were compared with previously characterized human strains.
L. monocytogenes was isolated from 11 (three manufacturers) of 56 products analysed. This included gravad salmon products from three manufacturers and cold-smoked salmon from one manufacturer. The highest level of L. monocytogenes found was 1500 cfu/g from a cold-smoked salmon product but the level was low (<100 cfu/g) in most of the products. Serovar 1/2a was predominant,
followed by 4b. Three products of gravad salmon harboured more than one serovar. PFGE typing of the 56 salmon isolates detected five Asc I types: four types were identical to human clinical strains with Asc I and one was identical and one was closely related to human clinical strains with Apa I. Isolation of identical or closely related L. monocytogenes strains from human clinical cases of listeriosis and gravad and cold-smoked salmon suggested that these kinds of products are possible sources of listeriosis in Sweden. Therefore, these products should be considered risk products for human listeriosis.

Listeria monocytogenes, a food-borne pathogen

Background: This study was conducted to examine the frequency of contamination in retail meat available in Karachi, Pakistan. Methodology: Raw meat samples (250) and surface swabs (90) from meat processing equipment and the surrounding environment were analyzed for microbiological contamination. Results: Out of 340 samples, 84% were found to be contaminated with bacterial species, including Klebsiella, Enterobacter, Staphylococcus aureus and Bacillus subtilis. A total of 550 (66%) of the bacterial isolates were potential pathogens. Of these, 342 and 208 isolates were from meat and environmental samples respectively. Food-borne pathogens isolated from meat samples included Escherichia coli O157:H7, Listeria, Salmonella Enteritidis and Shigella species whereas environmental samples yielded Staphylococcus aureus and Shigella species. Four strains of Brucella species were also isolated from meat samples. Total aerobic counts ranged between 10 8 –10 10 CFU/g or cm 2 . Resistance to a wide range of antibiotics was observed. Resistance rates to ampicillin, amoxicillin, novobiocin and cefaclor were from 62 to 75% in general. Thirty-three percent of Salmonella isolates were resistant to ampicillin. No quinolone resistance was observed. Biofilm formation was observed among 88 (16%) pathogenic bacteria including E. coli, Klebsiella, Enterobacter species and Staphylococcus aureus. Conclusions: Food-borne pathogens found in retail shops could be sources for horizontal contamination of meat. Our data confirm the circulation of antibiotic resistant and biofilm forming pathogens in raw meat and its environment in retail shops in Pakistan, which could play a role in the spread of antimicrobial resistance amongst food-borne bacteria.

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Microbial contamination of raw meat and its environment in retail shops in Karachi, Pakistan.

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 strain...

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

Aims

To provide molecular and phenotypical characterization of Enterococcus isolates obtained from raw milk and cheese, regarding their bacteriocinogenic and virulence activity.



Methods and Results

Forty-three bacteriocinogenic enterococci isolates were identified by 16s rDNA, fingerprinted by RAPD-PCR analysis and tested by PCR for the presence of genes for lantibiotics (lanM, lanB and lanC) and enterocins (entA, entB, entP, entL50AB and entAS48) and by phenotypical methods for bacteriocin production and inhibitory spectrum. Also, the virulence of the isolates was evaluated by PCR for genes gelE, hyl, asa1, esp, cylA, efaA, ace, vanA, vanB, hdc1, hdc2, tdc and odc and by phenotypical tests for gelatinase, lipase, DNAse and α- and β-haemolysis. Most isolates (93·0%) harboured at least one lantibiotic or enterocin gene and were positive for several tested virulence genes, mainly asa1 (100%), gelE (93·0%) and efaA (83·7%). 53·5% of the isolates presented β-haemolysis.



Conclusions

Enterococcus spp. isolates presented an interesting potential application for food preservation because of bacteriocin production; however, virulence-related genes were identified in all RAPD profiles.



Significance and Impact of the Study

The study demonstrated the contradictory characteristics of the tested Enterococcus isolates: they presented a good potential for application in food biopreservation but contained several virulence factors.

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Bacteriocinogenic and virulence potential of Enterococcus isolates obtained from raw milk and cheese.

Occurrence and characterization of Listeria spp. in ready-to-eat retail foods from Vancouver, British Columbia

Listeria monocytogenes: Occurrence in beef and identification of the main contamination points in processing plants

O objetivo desta pesquisa foi estabelecer a ocorrencia de Listeria monocytogenes em diversos pontos de plantas de processamento de carne bovina em 01 abatedouro e 05 casas de carnes localizados na regiao norte do Parana. Para a deteccao de Listeria spp. em 124 amostras de equipamentos/utensilios e instalacoes, utilizou-se a metodologia preconizada pelo United States Departament of Agriculture (USDA), com identificacao das especies por testes bioquimicos e posterior confirmacao pelo API Listeria (bioMerieux). Os resultados obtidos indicaram frequencias de 6,25% de L. monocytogenes; 68,75% de L. innocua; 18,75% de L. welshimeri; 4,17% de L. seeligeri e 2,08% de L. grayi. As amostras positivas para L. monocytogenes tiveram origem em equipamentos de casa de carnes como caixas plasticas e amaciador.

Fabrício Amorim Monteiro

Papers

Listeria monocytogenes: Occurrence in beef and identification of the main contamination points in processing plants

Listeria spp. ocorrência em equipamentos e ambientes de processamento de carne bovina