Prevalence of Listeria spp. and antibiotic susceptibility of Listeria monocytogenes isolated from raw chicken and ready-to-eat chicken products in Jordan

Listeria monocytogenes is the causal agent of listeriosis, a disease that can be serious and is often fatal in susceptible individuals. The objective of the study was to determine the prevalence of Listeria spp. in raw chicken and ready-to-eat (RTE) chicken products in Amman, Jordan and the antimicrobial resistance of L. monocytogenes isolates. A total of 280 raw chicken and RTE chicken products (chicken-shawirma, chicken-burger, chicken-sausage and mortadella) were collected from Amman abattoir and local retail markets in Amman city. Listeria spp. were isolated by the conventional International Organization for Standardization (ISO) method and L. monocytogenes identified by biochemical and Polymerase Chain Reaction (PCR). Results of conventional method showed that out of total 280 samples, 141 (50%) were found to be contaminated with Listeria spp. [L. monocytogenes (18.2%), Listeria ivanovi (26.1%), Listeria grayi (3.5%), Listeria seeligeri (1.8), Listeria welshimeri (0.7%)]. The PCR confirmed all L. monocytogenes isolates (51 isolates: 15 from raw dressed broiler chicken, 23 from chicken-burger, 9 from chicken-sausage, and 4 from chicken-shawirma). Five of the tested L. monocytogenes isolates were resistance to two antibiotics (tilimicosin and tetracycline) among the ten tested antibiotics as determined by microbroth dilution method. The results presented in this study indicate the potential risk of contamination of RTE chicken products with L. monocytogenes.     

Occurrence and antibiotic resistance profiles of Listeria monocytogenes isolated from seafood products and market and processing environments in Iran

This study was designed to determine the occurrence of Listeria monocytogenes in popular seafood products and their market and processing environments. The frequency of L. monocytogenes contamination was found to be 4.83% in raw and 14.5% in RTE seafood products. In raw products, the prevalence of L. monocytogenes was significantly higher (P < 0.05) in freshwater fish (11.4%) than in seawater fish (1.80%) and shrimp (1.69%). Cold-smoked fish had the highest frequency of L. monocytogenes contamination among the RTE products. The microbial load of L. monocytogenes in seafood products was in the range of <0.3 to 1100 MPN/g; and did not exceed 100 MPN/g in most of the examined samples. The incidence of L. monocytogenes in environmental and personnel samples was 17.1% and 16.2% in markets, and 21.3% and 18.2% in processing plants, respectively. It was found that contamination of processed fish fillets and shrimp flesh with L. monocytogenes mainly originated from the processing environments, rather than the raw materials. In addition, the implemented cleaning procedures were insufficient to eliminate L. monocytogenes from the market and processing environments. Serological examinations revealed that serotype 1/2a (45.7%) was the predominant serotype of L. monocytogenes followed by 4b (40.3%), 1/2c (5.39%), 1/2b (4.68%), and 4c (3.96%). Regarding seasonal variability, 1/2a was the dominant serotype during warm seasons, whereas 4b was the most prevalent serotype during cold seasons. The isolates of L. monocytogenes were highly resistant to penicillin, ampicillin, tetracycline, and vancomycin. The results indicate that prevalence of L. monocytogenes serotypes 1/2a and 4b, which are associated with foodborne outbreaks of human listeriosis; and their resistance to commonly used antibiotics for treatment of human listeriosis could be a public health concern.     

Increase over time in the prevalence of multiple antibiotic resistance among isolates of Listeria monocytogenes from poultry in Spain

The aim of this study was to determine and compare the antibiotic resistance profiles of Listeria monocytogenes isolates obtained from poultry in North-Western Spain in 1993 and 2006. The prevalence of Listeria spp. and L. monocytogenes was also investigated. A total of 202 samples were analysed (100 in 1993 and 102 in 2006). Samples taken in 1993 and 2006 showed a similar (P > 0.05) prevalence for both Listeria spp. (95.0% and 92.1%, respectively) and L. monocytogenes (32.0% and 24.5%). In both 1993 and 2006 the species most frequently detected was Listeria innocua, followed by L. monocytogenes. Other species isolated were Listeria welshimeri, Listeria grayi and Listeria ivanovii. L. monocytogenes isolates (68) were tested by disc diffusion assay for their resistance to 15 drugs currently used in veterinary and human therapy. All isolates displayed resistance to at least one antibiotic. Excluding nalidixic acid, to which most strains are intrinsically resistant, 37.2% of strains in 1993 and 96.0% in 2006 showed resistance to at least one antibiotic. Multi-resistance (resistance to two or more antibiotics) was less common in 1993 than in 2006 (18.6% and 84.0%, respectively; P < 0.001). The average number of antibiotics to which the strains were resistant was lower (P < 0.001) in 1993 (1.6) than in 2006 (4.2). An increase (P < 0.05) in the percentage of resistant strains was observed between 1993 and 2006 for six different drugs: gentamicin, streptomycin, neomycin, enrofloxacin, ciprofloxacin and furazolidone. In this research, the prevalence and the antibiotic susceptibility of L. monocytogenes in poultry samples from the same origin in North-Western Spain in the 1990s and the 2000s were compared for the first time. The increase in antibiotic resistance from 1993 to 2006 constitutes a matter for concern and confirms a general worldwide pattern among many groups of bacteria. The high prevalence of L. monocytogenes in poultry suggests the crucial role of food handlers in preventing listeriosis in consumers. Reducing the prevalence of L. monocytogenes in poultry and preventing the emergence or selection of antibiotic-resistant strains are also highlighted.     

Genotypic characterization of Listeria monocytogenes isolated from milk and ready-to-eat indigenous milk products

Listeria monocytogenes is a food borne pathogen associated with severe diseases in humans and animals. We present the genotypic analysis of 18 L. monocytogenes isolates recovered from milk and ready-to-eat (RTE) indigenous milk products by multiplex-PCR, allowing serovar predictions, and by random amplification of polymorphic DNA (RAPD) assays. Multiplex-PCR serotyping assay revealed 72.2% (13/18) strains belonging to serovar group 4b, 4d, 4e, 22.2% (4/18) to serovar group 1/2b, 3b while 5.5% (1/18) to serovar group 1/2a, 3a. RAPD analysis revealed five RAPD profiles from eight L. monocytogenes strains from milk, and seven RAPD profiles from ten strains from milk products. Though RAPD analysis allowed discrimination among isolates of the same serotype and among isolates from the same sampling areas or those isolated from different areas, our results suggests that most of the L. monocytogenes isolates were indeed sporadically harboured by single food items. Thus, RAPD together with multiplex-PCR serotyping allowed rapid discrimination of L. monocytogenes strains and therefore could serve as an economical tool for typing L. monocytogenes strains. In addition, the predominance of L. monocytogenes serotype 4b in our study is of public health concern, as this serotype has been most frequently associated with human listeriosis.     

Occurrence and traceability of Listeria monocytogenes strains isolated from sheep's milk cheese-making plants environment

The aim of the study was to conduct an extensive survey on Listeria monocytogenes and Listeria spp. environmental contamination in 13 cheese-making plants. A total of 409 environmental and food samples were collected during years 2011–2013. Listeria spp. contamination was observed in all the facilities, while L. monocytogenes was recovered from 12 facilities with a prevalence ranging between 3.0% and 22.6%. Floor drains were the most contaminated sampling sites (48.8% of positive samples), serving as harbourage site for subsequent contamination. Out of 616 isolates, 277 (45.0%) were Listeria innocua, 274 (44.5%) L. monocytogenes, 41 (6.6%) Listeria ivanovii, 14 (2.3%) Listeria welshimeri and 10 (1.6%) Listeria gravyi. Serotyping carried out by PCR and agglutination method for L. monocytogenes revealed that 169 strains (61.7%) were serotype 1/2a, 65 (23.7%) 4b, 20 (7.3%) 1/2b, 10 (3.6%) 3a, 7 (2.5%) 1/2c and 3 (1.1%) 3b. PFGE conducted on L. monocytogenes isolates using AscI and ApaI restriction enzymes, yielded 6 clusters. Two predominant PFGE clusters were observed including respectively 36 and 32 strains. Within cheese-making plants, L. monocytogenes showed wide variability with strains distributed up to 4 different clusters. Pulsotypes isolated from raw milk filter were never detected in the processing environment, indicating that the contamination originated from sources other than raw milk. The isolation of strains with similar profile from different sampling sites, within and among cheese-making plants, indicated the possible transfer of L. monocytogenes contamination along production lines and from one facility to another. Strains recovered from food were confirmed as originating from the processing environment.     

Growth inhibition effects of ferulic acid and glycine/sodium acetate on Listeria monocytogenes in coleslaw and egg salad

Listeria monocytogenes is a bacterium responsible for food poisoning through ready-to-eat (RTE) food products. In particular, salads are RTE products that lead to many cases of listeriosis. Such concerns have made it necessary to find a method of inhibiting Listeria growth. In this study, coleslaw and egg salads were inoculated with L. monocytogenes, followed by addition of either ferulic acid or ferulic acid + glycine/sodium acetate, and were incubated at 10 °C for a maximum of 5 days. In coleslaw, the addition of 1500 ppm ferulic acid resulted in a 1.5 log CFU/g reduction in L. monocytogenes after 5 days. In egg salad, for 5 days following the addition of 3000 ppm ferulic acid + 1% glycine/sodium acetate compound, no additional L. monocytogenes growth was observed. This study demonstrates that under particular conditions, ferulic acid has anti-bacterial properties against L. monocytogenes. Our results suggest that ferulic acid could be highly useful for inhibiting the growth of L. monocytogenes in salad products.     

Prevalence,antibiotic resistance and genetic diversity of Listeria monocytogenes isolated from retail ready-to-eat foods in China

Listeria monocytogenes is a major foodborne pathogen that is well known as high mortality rate upon infected. This study aimed to investigate the prevalence of L. monocytogenes isolates from retail ready-to-eat (RTE) foods in China and characterize the isolates of L. monocytogenes by antibiotic resistance, serotyping, ERIC-PCR and REP-PCR subtyping analyses. From September 2012 to January 2014, a total of 364 retail RTE foods were obtained. Using the qualitative and quantitative methods, 25 samples (6.87%) were positive for L. monocytogenes. The identity of isolates of L. monocytogenes was confirmed by PCR. All 80 isolates in this survey were sensitive to penicillin and mezlocillin, the highest resistance is clindamycin (51.25%), followed by cephalothin (23.75%) and ampicillin (12.5%). Twenty-seven isolates were susceptible to all 14 tested antibiotics; seventeen isolates were resistant to more than two antibiotics, including six multiresistent strains resist to more than 10 antibiotics. L. monocytogenes isolates belonged to serovar types 1/2a (3a), 4b (4d, 4e), 1/2b (3b, 7) and 1/2c (3c). 29 L. monocytogenes isolates were selected by serotyping. At the relative similarity coefficient of 0.80, it grouped 29 isolates and 5 reference strains into 2 clusters and 3 singletons, 4 clusters and 1 singleton by ERIC-PCR and REP-PCR, respectively. Our study reflects the potential risk of L. monocytogenes infection in China. We also provide a comprehensive surveillance on its incidence on the RTE foods of L. monocytogenes and ensure more accurate treatment of human listeriosis with effective antibiotics.     

Successful management of Listeria spp. in an avocado processing facility

Listeria monocytogenes can grow and multiply in various food matrices and cause severe human illness. Apart from the influence on consumer health, L. monocytogenes contamination of ready-to-eat (RTE) food products causes major economic losses due to product recalls. Control of foodborne pathogens in RTE food products is a challenge, specifically in foods that cannot undergo a heat-treatment during processing. The aim of this study was to develop control strategies for the management of L. monocytogenes in an avocado processing facility, additional to a quality control system. An in-house monitoring system (IMS) was established to test specifically for Listeria spp. in the final products and processing environment, including floors, equipment, work areas and personnel. Guacamole and environmental samples were collected and tested on-site for Listeria with the ISO 11290-1 method. Based on the prevalence of Listeria, the facility introduced new strategies in processing to counter cross contamination. Results from the 2014 guacamole production season showed almost complete eradication of Listeria spp. in final products (0.17%, n = 1170) and the processing facility (0.79%, n = 1520). This is a major achievement since the highest incidence of Listeria spp. over a period of five years was measured at 11.39% (n = 948) in the final product during the 2013 season and 13.44% (n = 1927) in the processing facility in 2011. These results indicate that successful management of Listeria spp. in an avocado processing facility can be accomplished with in-house monitoring of the listerial population and subsequent adjustments to the processing system.     

Invasiveness of Listeria monocytogenes strains of Caco-2 cells in response to a period of extreme salt stress reflecting salt-curing and rehydration of cod (Gadus morhua L.)

Products like salt-cured fish contain approximately 15–21% NaCl and are rehydrated to 2–3% NaCl before preparation and consumption. These products are regarded as safe, but it has been shown that Listeria spp. is able to survive at extreme levels of salt and start to grow after rehydration. Thus, the ability of salt stressed Listeria monocytogenes to cause listeriosis, measured as its ability to invade Caco-2 cells was studied in this paper. Seven strains of L. monocytogenes and one Listeria innocua were cultivated in BHI to early and late stationary phase at 4 °C. At both phases, the strains were exposed to either no salt or to salt stress comparable to that applied in the production of rehydrated salt-cured cod, i.e. 21% NaCl followed by dilution to 2% NaCl. In addition, the eight strains were cultivated in BHI with 2% NaCl, which is similar to the salt content as in rehydrated salt-cured cod and other ready-to-eat (RTE) products as well. The ability of non salt stressed L. monocytogenes strains to enter Caco-2 cells was significant higher (p > 0.05) compared to the corresponding strains exposed to 21% NaCl for 96 h, followed by 2% NaCl for 48 h. On the other hand, L. monocytogenes cultivated in BHI with 2% NaCl showed a higher invasiveness of Caco-2 cells than both the other sample categories. As the ability to invade Caco-2 cells correlates with bacterial virulence, the results suggests that L. monocytogenes represent a lower food safety risk when exposed to salt-curing with extreme NaCl concentrations than exposure of a constant and moderate level of salt commonly used in RTE products.     

Investigation on prevalence of Listeria spp. and Listeria monocytogenes in animal-derived foods by multiplex PCR assay targeting novel genes

Chilled and frozen animal-derived food can be contaminated by Listeria spp., emerging foodborne pathogens in food industry. The objective of this study was to mine novel target genes by comparative genomics approach for multiplex PCR detection and differentiation of Listeria monocytogenes and other Listeria spp. in food. Multiplex PCR assay targeting the genetic markers LMOf2365_2721, AX25_00730, lin1814, int, lwe1673, and Oxidoreductase gene, resulted in the amplification of DNA fragments of 583 bp, 703 bp, 421 bp, 994 bp, 345 bp, and 201 bp from L. monocytogenes, Listeria ivanovii, Listeria innocua, Listeria seeligeri, Listeria welshimeri, and Listeria grayi, respectively. The detection limits of the multiplex assays were as low as 89 fg/μL genomic DNA and 910 CFU/mL of bacterial culture. The prevalence of Listeria spp. was determined using the developed multiplex PCR assay and standard microbiological method in a total of 200 food samples collected from different supermarkets and traditional agri-product markets in Nanjing, China. A total of 28 samples were found to be positive for the presence of Listeria, including 10.9% (6/55) of livestock meat samples, 22% (11/50) of poultry samples, 15% (6/40) of shellfish samples, 13.3% (4/30) of octopus samples and 4% (1/25) of freshwater fish samples. Of these, 13 isolates were classified as L. monocytogenes, 11 were classified as L. innocua, 2 were classified as L. ivanovii and 3 were classified as L. welshimeri. These results demonstrate that the multiplex PCR assay based on novel target genes is able to rapidly detect the Listeria spp. in 12 h with high accuracy and sensitivity, which may be used in the future for detection of Listeria spp. in animal-derived food products.     

Antimicrobial resistance profiles of Listeria monocytogenes isolated from ready-to-eat products in Poland in 2007–2011

The aim of the study was to characterize strains of Listeria monocytogenes isolated from ready to eat (RTE) products collected as part of official food control and monitoring in Poland. A total of 105 L. monocytogenes isolates from RTE products: 54- cakes and 51 – delicatessen products were examined. The presence L. monocytogenes in cakes and delicatessen products was 0.4% and 0.7% respectively suggesting the level of contamination of RTE products with L. monocytogenes is very low.     

Prevalence of Listeria spp. in ready to eat foods (RTE) from Algiers (Algeria)

The aim of this study was to establish the occurrence of Listeria spp., especially Listeria monocytogenes in ready to eat RTE food marketed in Algiers (Algeria).A total of 227 samples were collected from different producers and retailers.All samples were analyzed using a conventional cultivation method AFNOR V08-055.Out of 227 samples tested, 21 (9.3%) tested positive for Listeria spp. among them, 6 (2.6%) tested positive for L. monocytogenes. L. innocua was the most common Listeria species found being detected in 11 samples (4.8%), although both Listeria ivanovii and Listeria welshimeri were detected in 3 (1.3%) and 1 (0.4%) food samples respectively.The study of the antimicrobial sensitivity of Listeria monocytogenes strains showed no resistance.The study has enabled us to detect these contaminants in a wide range of RTE foods, to suggest that contamination likely occurs after heat treatment, and to assess the danger represented by this category of food for populations at risk.     

Simultaneous detection of Listeria species isolated from meat processed foods using multiplex PCR

Listeriosis is a foodborne disease caused by the pathogenic Listeria monocytogenes and is considered as a serious health problem due to the severity of symptoms and its high mortality rate. Listeria genus is divided into six species and especially L. monocytogenes is an important foodborne pathogen in humans and livestock. Recently, other Listeria species are reported as pathogenic strains in decayed foods and environments as well. High mortality rate of listeriosis demands for rapid methods to detect the potential presence of the food pathogens in the food industry. We have developed a multiplex PCR for rapid and simultaneous detection of six Listeria species including Listeria grayi, Listeria innocua, Listeria ivanovii, L. monocytogenes, Listeria seeligeri and Listeria welshimeri to identify specific Listeria species in processed foods. The optimized multiplex PCR in this study utilized one Listeria genus specific and each Listeria species-specific primer pairs. Each primer pair yields the products of 370-bp for Listeria genus-specific, 201-bp for L. grayi-specific, 749-bp for L. innocua-specific, 463-bp for L. ivanovii-specific, 509-bp for L. monocytogenes-specific, 673-bp for L. seeligeri-specific and 281-bp for L. welshimeri-specific. We have successfully applied multiplex PCR strategy to 93 Listeria isolates from processed meat products to determine specific Listeria species and out of which 81 strains of L. monocytogenes, 10 strains of L. innocua and 2 strains of L. welshimeri were identified. This established multiplex PCR provides rapid and reliable results and will be useful for the detection of Listeria species in contaminated food products and clinical samples.     

Prevalence and characterization of Listeria monocytogenes isolated from retail food in Henan,China

Listeria monocytogenes, an important foodborne pathogen, is the causal agent of listeriosis. In this study, a total of 954 food samples originating from raw meat, cooked meat products, seafood, and vegetables purchased from supermarkets and open-air markets in Henan province, China, were analyzed for the presence of L. monocytogenes. All L. monocytogenes isolates were subjected to serotyping, pulsed-field gel electrophoresis (PFGE), and antimicrobial resistance. The overall percentage of L. monocytogenes prevalence was 6.2% (n = 59) with the highest rate of 7.4% for cooked meat products followed by raw meat (6.7%). The isolates belonged to five serotypes (1/2a, 1/2b, 1/2c, 4b, and 4c), with serotype 1/2a being predominant (55.9%). PFGE revealed a low genetic diversity among the isolates, irrespective of their sources, suggesting that dominant clones are widespread in different food products in Henan. Resistance to cefotaxime (30.5%) and ciprofloxacin (13.5%) was most often, whereas resistance to tetracycline, trimethoprim/sulfamethoxazole, and erythromycin was observed less frequently. The presence of L. monocytogenes in food products and antimicrobial resistance among the isolates represents a potential public health risk. Our results indicate that effective hygienic measures and bacteriological controls are necessary in China to reduce the contamination of retail food samples by L. monocytogenes.     

Prevalence and characterization of Listeria monocytogenes isolated from retail-level ready-to-eat foods in South China

Listeria monocytogenes is an important food-borne pathogen causing meningitis, meningoencephalitis and abortion. To assess the potential risk to consumer health, the presence of L. monocytogenes was investigated using qualitative and quantitative methods. Ten (6.33%) of 158 retail RTE food samples were positive for L. monocytogenes and the contamination levels were less than 10 MPN/g,while none of 65 dairy products was positive for L. monocytogenes. The 37 strains were grouped into five clusters and two singletons, five clusters and two singletons, and three clusters and one singleton by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) and RAPD fingerprint respectively, at similarity coefficient of 80%. The susceptibility test showed that 83.8% were susceptible to 15 antimicrobials; two were penicillin-resistant, and one was multidrug-resistant to kanamycin, tetracycline, sulfamethoxazole, rifampin, gentamycin, penicillin, and ampicillin. Virulent L. monocytogenes that possess partial antimicrobial resistance, and serotypes frequently associated with listeriosis were recovered from RTE foods. Consumers may, therefore, be exposed to potential risks of L. monocytogenes infection in South China. This study contributed to the prevalence and contamination levels of L. monocytogenes in RTE foods in South China for the first time, providing baseline information for Chinese regulatory authorities to formulate a regulatory framework for controlling L. monocytogenes to improve the microbiological safety of RTE foods.     

Genotypic characterization and antimicrobial resistance of Listeria monocytogenes from ready-to-eat foods

Listeria monocytogenes is an important foodborne pathogen. The aims of this study were to determine genetic relatedness of L. monocytogenes isolated from ready-to-eat (RTE) foods in Malaysia. L. monocytogenes isolates from RTE foods were characterized by multiplex-PCR serotyping, REP-PCR, BOX-PCR, RAPD, PFGE, virulotyping and antibiotyping. Of the 32 L. monocytogenes isolates analyzed, 21 (65.6%) were assigned to serogroup “1/2a, 3a”, seven (21.9%) serogroup “1/2c, 3c”, and four (12.5%) serogroup “4b, 4d, 4e”. All the L. monocytogenes harbored inlA, inlB, inlC and inlJ virulence genes. More than half (53%) L. monocytogenes isolates were resistant to penicillin G, followed by tetracycline (15.6%), amoxicillin-clavulanic acid (12.5%), vancomycin (9.4%) erythromycin (6.3%), clindamycin, streptomycin, kanamycin, and chloramphenicol (each 3.1%). REP-PCR, BOX-PCR, RAPD and PFGE generated 28 (D = 0.992), 31 (D = 0.998), 32 (D = 1), and 20 (D = 0.916) patterns, respectively. These results indicate that L. monocytogenes isolates from RTE food were heterogeneous. There was no correlation between antibiograms and serogroups or pulsotypes or PCR-typing and/or sources of isolates. Since different subtyping methods often give different discriminatory powers, the use of more than one subtyping approach is necessary in providing a more accurate picture of the genetic diversity of L. monocytogenes. In conclusion, L. monocytogenes isolates from RTE possess the internalin genes and are genetically diverse. Furthermore, the occurrence of resistant isolates belonging to epidemiologically important serogroups “1/2a, 3a” and “4b, 4d, 4e” in RTE foods is a matter of public health concern.     

Occurrence of Listeria spp. in dairy plants in Southern Italy and molecular subtyping of isolates using AFLP

We report the detection of Listeria spp. and Listeria monocytogenes in 34 dairy plants. In total, 547 of food, product contact surface and floor drain samples were collected along the product lines. Nineteen cheese factories (55.8%) were contaminated by Listeria spp. Of these 20.6% were L. monocytogenes positive. Listeria spp. was found in 6.8% of food samples, 11.3% of product contact surfaces and 40.6% of floor drains. L. monocytogenes was found in 2.4% of food samples, 4.9% of product contact surfaces and 18.8% of floor drains. Twentyfive L. monocytogenes isolates were serotyped using commercial specific antisera and genotyped using Amplified Fragment Length Polymorphism (AFLP) analysis. AFLP genotyping discriminated the four species of Listeria isolated and different genotypes for each species, moreover it could identify persistent genotypes in some dairy facilities. Listeria spp. and L. monocytogenes are widely spread in the dairy sector and probably contaminate foods during the production process. Facility-based monitoring can identify possible routes of transmission and thus allow establishment of more effective strategies to prevent food contamination.     

Changing regulation: Canada's new thinking on Listeria

In 2008, Canada experienced one of its most serious outbreaks of foodborne listeriosis. During this outbreak, which was eventually traced back to contaminated deli-meat, there were 57 cases of illness and 23 deaths. As a result of the outbreak, the Canadian Food Inspection Agency (CFIA) has developed new Directives for the registered meat and poultry sector. Under the new requirements, production facilities must implement food contact surface testing for Listeria spp. and/or Listeria monocytogenes. The enhanced requirements focus on early detection and control of L. monocytogenes by introducing new testing and reporting requirements for industry, e.g., positive test results from all food contact surface testing must now be immediately reported to the CFIA and companies must perform trend analysis on their test results.In addition, work has begun on updating the current Health Canada policy on L. monocytogenes. The Canadian approach to Listeria control stresses the importance of environmental sampling. In addition to government agencies and food industries working diligently at minimizing the exposure to L. monocytogenes, consumers also have an important role to play in the farm-to-fork continuum. That role calls for Canadians to learn and adopt safe food handling, avoidance of certain high-risk foods, and preparation practices. To this effect, Health Canada has and will continue to undertake the development of science-based consumer education material which will help create an understanding of food safety issues within the context of the public’s right to know about the potential dangers in food, and industry’s responsibility for producing safe food. A combination of all these approaches are currently being adopted and/or developed to improve the control of L. monocytogenes in RTE foods sold in Canada.     

Prevalence and antimicrobial resistance of Listeria species isolated from milk and dairy products in Iran

The objective of this study was to determine the prevalence of Listeria spp. in milk and dairy products in Isfahan province, Iran. From March 2007 to September 2009, a total of 594 samples of various milk and dairy products were obtained from randomly selected retail stores. Using conventional bacteriologic method, 55 samples (9.3%) were positive for Listeria spp. The highest prevalence of Listeria was found in raw sheep milk samples (22.6%), followed by cheese samples (18.9%). The most species recovered was Listeria innocua (58.2%); the remaining isolates were Listeria monocytogenes (32.7%) and Listeria seeligari (9.1%). Overall, 54 Listeria isolates (98.2%) were resistant to one or more antimicrobial agents. Resistance to nalidixic acid was the most common finding (96.4%). All Listeria isolates were susceptible to vancomycin. The results of this study indicate the potential risk of infection with Listeria in people consuming raw and unpasteurized milk and dairy products.     

Incidence and genetic variability of Listeria species from three milk processing plants

The presence of Listeria in three milk processing environments as a potential source of milk contamination was assessed. Swab samples (n = 210) taken from milk processing plants were examined. Sample sites included the milk processing equipment, besides areas handling raw and pasteurized milk. The USDA Listeria-selective enrichment procedure was used to process the samples. Forty one (19.52%) Listeria isolates were recovered. The isolates were further subjected to biochemical and genotypic characterization. Out of 41 isolates, 16 (7.62%) were confirmed as Listeria monocytogenes, 2 (0.95%) as L. ivanovii, 19 (9.05%) as L. innocua. 1 (0.48%) as L. seeligeri and 3 (1.43%) as L. grayi. All the L. monocytogenes isolates were positive for the hlyA gene. PCR based serotyping revealed all L. monocytogenes to be of 1/2a, 1/2c, 3a and 3c serovar group. AscI and ApaI restriction analysis yielded four PFGE clusters for 16 L. monocytogenes isolates obtained from raw milk collector, milk silos, buttermilk mixer, cheese and other milk product processor. No predominant PFGE cluster was observed among these L. monocytogenes isolates. The main sources of L. monocytogenes were found to be raw milk collector and milk silos. In the present study L. monocytogenes was isolated from milk and milk products processing plants which could cross-contaminate the processed products and may possess a potential threat to public health.