Listeria species in raw and ready-to-eat foods from restaurants

From September 1999 to March 2000, meat (pork, beef, and chicken), fish (salmon, hake, and sole), vegetable (lettuce and spinach), and Spanish potato omelette samples obtained at restaurants were collected and tested for the occurrence of Listeria spp. Listeria monocytogenes was isolated from 3 (2.9%) out of 103 studied samples. Other species isolated were Listeria grayi (13.6%), Listeria innocua (1.9%), Listeria ivanovii (5.8%), Listeria seeligeri (3.9%), and Listeria welshimeri (1.9%). Listeria was neither isolated from beef nor any type of fish.     

Prevalence and contamination levels of Listeria monocytogenes in smoked fish and paté sold in Spain.

From March to November 2000, 170 samples of smoked fish and 182 samples of paté for sale in retail outlets and supermarkets in the nine provinces of Castilla and León (Spain) were analyzed for the prevalence of Listeria monocytogenes and other Listeria spp. L. monocytogenes was isolated from 38 (22.3%) of the 170 samples of smoked fish analyzed. Twenty of these positive samples contained L. monocytogenes at >100 CFU/g. Other Listeria spp., such as Listeria innocua (26 isolates), Listeria grayi (9), Listeria welshimeri (3), Listeria seeligeri (3), and Listeria ivanovii (2), were also detected. L. monocytogenes was isolated from 5.4% of the 182 samples of paté. Only 1 of the 10 positive samples harbored >100 L. monocytogenes CFU/g. Two other species of Listeria were observed in paté: L. innocua (12 isolates) and L. grayi (2).     

INCIDENCE OF LISTERIA SPECIES IN INDIAN SEAFOODS AND MEAT

Thirty eight samples of fresh, frozen and dry seafoods and 27 samples of fresh and cold stored meat and meat products obtained from retail shops were examined for the presence of Listeria spp. Direct plating of the sample homogenate on Listeria Selective Agar (LSA) was compared with the two step enrichment method devised by Hao et al. for detecting Listeria spp. in vegetables. We report that modification of this methodology involving cold enrichment for 48 h in Brain Heart Infusion (BHI) at 10C followed by enrichment at 37C in Listeria enrichment broth (LE) resulted the enumeration of a large population of Listeria from flesh foods. Listeria isolates from fish and meat were identified by employing the cultural methods given in modified version of the Bacteriological Analytical Manual (Lovett and Hitchins 1988). Listeria spp. from seafoods were identified, with the order of predominance as L. grayi, L. innocua, L. murrayi, L. seeligeri. Samples of meat and their products were found to be contaminated mainly with L. innocua and L. murrayi. In contrast, screening of an independent batch of 20 fish and meat samples by adopting the PHLS (UK) method revealed predominance of L. grayi and L. seeligeri in fish and presence of additional species like L. seeligeri, L. ivanovii and L. welshimeri in meat products. None of the methods however could detect incidence of L. monocytogenes in any of the samples tested from local market in Bombay.     

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

The occurrence of Listeria spp. and Listeria monocytogenes in retail RTE meat and fish products in Vancouver, British Columbia (B.C.) was investigated. To assess potential consumer health risk, recovered L. monocytogenes isolates were subjected to genotypic and phenotypic characterization. Conventional methods were used to recover Listeria spp. from deli meat (n = 40) and fish (n = 40) samples collected from 17 stores. Listeria spp. were recovered only from fish samples (20%); 5% harboured Listeria innocua, 5% had L. monocytogenes and 10% contained Listeria welshimeri. L. monocytogenes isolates serotyped as 1/2a and 1/2b, possessed dissimilar PFGE patterns, and had full-length InlA. Three 1/2a clonal isolates encoded the 50 kb genomic island, LGI1. Antimicrobial resistance (AMR) profiling showed all Listeria spp. possessed resistance to cefoxitin and nalidixic acid. L. monocytogenes were resistant to clindamycin, two were resistant to streptomycin, and one to amikacin. Reduced susceptibility to ciprofloxacin was seen in all L. monocytogenes, L. innocua and three L. welshimeri isolates. Reduced susceptibility to amikacin and chloramphenicol was also observed in one L. monocytogenes and three L. welshimeri isolates, respectively. Recovery of L. monocytogenes in fish samples possessing AMR, full-length InlA, LGI1, and serotypes frequently associated with listeriosis suggest B.C. consumers are exposed to high-risk strains.     

Incidence and susceptibility to antimicrobial agents of Listeria spp. and Listeria monocytogenes isolated from poultry carcasses in Porto,Portugal

The occurrence of Listeria spp. and Listeria monocytogenes in 63 samples of Portuguese poultry carcasses obtained from two local butcher shops and one canteen in the city of Porto, Portugal, and the susceptibility of these bacteria to antimicrobial agents allowed for use in human or animal therapeutics were evaluated. All poultry samples were contaminated with Listeria spp., and L. monocytogenes was isolated from 41% (26 of 63) of the samples. Other Listeria species, including L. innocua, L. welshimeri, and L. seeligeri, were also isolated from poultry samples. A multiplex polymerase chain reaction method was used for the identification of all of the Listeria isolates; this method showed total conformity with the conventional method of biochemical identification and proved to be more reliable, faster, and less arduous. In addition, high percentages of Listeria spp. (84%) and L. monocytogenes (73%) isolates were found to be resistant to one or more antimicrobial agents of different groups, and 12 different resistance profiles were recorded. The frequency of the resistance of L. monocytogenes isolates to enrofloxacin and clindamycin is notable. The results of this study suggest a high incidence of L. monocytogenes on Portuguese poultry products available for consumers and indicate that poultry could be a potential vehicle of foodborne infections due to strains of L. monocytogenes that are resistant to antimicrobial agents.     

Temperature gradient gel electrophoresis of the amplified product of a small 16S rRNA gene fragment for the identification of Listeria species isolated from food

The development of a rapid method for the identification of Listeria spp. is described. It is based on the polymerase chain reaction amplification of a small fragment from the 16S rRNA gene followed by temperature gradient gel electrophoresis. Forty-five strains of Listeria spp. (Listeria monocytogenes, Listeria innocua, Listeria ivanovii, Listeria seeligeri, and Listeria welshimeri) were used for the optimization of the protocol. No differences were observed between the results of the identification of the strains tested using traditional methods and those obtained by polymerase chain reaction-temperature gradient gel electrophoresis analysis.     

The occurrence in the U.K. of Listeria species in raw chickens and soft cheeses

Retail samples of 100 raw chickens and 222 U.K. and imported soft cheeses were examined for the presence of Listeria species. 60% of raw chickens (fresh and frozen) were contaminated with L. monocytogenes and 28% with other Listeria spp. including L. welshimeri, L. seeligeri and L. innocua. Six serotypes of L. monocytogenes were represented (1/2, 3a, 3b, 3c, 4b, 4d) of which more than one were isolated from some samples. 10% of the soft cheeses examined were found to contain L. monocytogenes at levels from less than 10(2) cfu/g to 10(5) cfu/g. The incidences in cheeses from various countries were Italy (16%), France (14%), Cyprus (10%) and the U.K. (4%). Only 2 serotypes (1/2 and 4b) were isolated, some samples containing both. L. innocua was the only other Listeria sp. found. There was no correlation between either the contamination with E. coli or the processing of the original milk used to make the cheeses (raw or pasteurized) and the presence of L. monocytogenes or other Listeria spp. The contribution of contaminated food to the epidemiology of listeriosis in the U.K. is discussed.     

Occurrence and Antimicrobial Susceptibility of Listeria monocytogenes Isolated from Brined White Cheese in Jordan

Listeria monocytogenes is a serious foodborne pathogen that has been isolated from different dairy food products. Several foodborne outbreaks of listeriosis have been associated with consumption of cheese. The aims of this study were to determine the occurrence of L. monocytogenes and Listeria spp. in brined white cheese (BWC) sold in Jordan, and to determine the susceptibility of isolated L. monocytogenes to antimicrobials. Three hundred and fifty samples of 5 different types of BWC (akkawi, boiled, halloumi, pasteurized, and shellal) were collected from a local market in Jordan. The ISO (11290-1) procedure was followed for isolation and identification of Listeria spp. from cheese samples and a polymerase chain reaction (PCR) technique was used for confirmation of L. monocytogenes isolates. The VITEK2 automated system was used for testing antimicrobial susceptibility of L. monocytogenes isolates. The overall prevalence of Listeria spp. in cheese sample was 27.1%. L. monocytogenes was isolated from 39 (11.1%) samples. Other isolated species were L. grayi (6.9%), L. innocua (2%), L. ivanovii (4%), L. seeligeri (2%), and L. welshimeri (0.3%). The pH values and salt concentrations of L. monocytogenes positive cheese samples ranged from 5.10 to 6.32 and 5.64 to 13.16, respectively. L. monocytogenes isolates were sensitive or intermediate susceptible to imipenem, gentamicin, linezolid, teicoplanin, vancomycin, fusidic acid, trimethoprim/sulfamethoxazole, benzylpenicillin, ciprofloxacin, erythromycin, tetracycline, and rifampicin, but resistant to fosfomycin, oxacillin, and clindamycin.     

Incidence of Listeria species in seafood and seafood salads

A total of 128 samples of seafood on the Icelandic market were tested for the presence of Listeria monocytogenes and other Listeria species. The samples included raw, smoked and dried fish, frozen shellfish and shrimps as well as several fish salads. These products are generally consumed without heating. Listeria spp. were present in 56% of the samples of raw fish, 29% of the smoked fish, 9% of the shrimps and 32% of the salads. No Listeria spp. were present in the shellfish or dried fish. In 46% of the positive samples L. monocytogenes could be demonstrated, either alone or together with L. innocua. The other positive samples contained L. innocua and, in one sample, L. welshimeri. All products sampled had been processed and packed in Iceland, mostly for use on the domestic market. It is suggested that consuming certain fish products and fish salads may form an additional risk factor for listeriosis in humans.     

IMMUNOLOGICAL AND CYTOPATHOGENIC PROPERTIES OF LISTERIA MONOCYTOGENES ISOLATED FROM NATURALLY CONTAMINATED MEATS

Meat products have been implicated as the potential source of Listeria monocytogenes infection in humans. Here, we investigated the incidence of this organism in raw beef and poultry meat products and assessed their biochemical, immunological and cytopathogenic properties. Forty meat samples (20 beef and 20 poultry) were analyzed and the isolates were tested for sugar fermentation, hemolysin production, phospholipase activity, serotype profile, abilities to react with Listeria- specific monoclonal antibodies (MAbs) EM-7G1 and C11E9, and cytotoxic effects on hybridoma Ped-2E9 cells. Thirteen (6 beef and 7 poultry) meat samples (32.5%) were positive for L. monocytogenes. A total of 276 Listeria isolates were obtained, of which 182 (66%) were confirmed to be L. monocytogenes, 80 (29%) were L. innocua, 12 (4.3%) were L. welshimeri and 2 (0.7%) were identified as L. grayi. Fifty six percent of the L. monocytogenes isolates were serotype 4, while 42% were serotype 1, and 2% were untypeable. All but two L. monocytogenes isolates were hemolytic and phospholipase positive (99%). In the ELISA assay, MAb C11E9 showed reaction with L. monocytogenes isolates from all 13 positive meat samples (100%), while MAb EM-7G1 reacted positively with 12 of 13 positive meat samples (92.3%). Hemolysin-positive L. monocytogenes isolates were cytopathogenic to Ped-2E9 cells, while hemolysin-negative strains showed no effect. This study demonstrated that 32.5% of commercially purchased raw meat products were contaminated with cytopathogenic L. monocytogenes strains, and could be a potential source for infection in susceptible populations if these meats were not processed or cooked properly.