Incidence and characterization of Listeria monocytogenes from domestic and imported foods in Korea

A total of 1,537 domestic and imported food products were examined for the incidence of Listeria monocytogenes between 1993 and 1997 in Korea. L. monocytogenes was detected using the U.S. Department of Agriculture isolation method. Isolated L. monocytogenes was confirmed by polymerase chain reaction with hly1 and hly2 primers designed from the listeriolysin O. Overall, 122 samples (7.9%) contained L. monocytogenes. The rate of isolation was 4.3% for beef, 19.1% for pork, 30.2% for chicken, 1.2% for shellfish, 4.4% for raw milk, 4.4% for frozen smoked mussels, and 6.1% for ice cream. No L. monocytogenes was found in pasteurized milk, pasteurized processed cheese, saltwater fish, dried seafoods, or ham. The overall incidence was lower than that reported in previous studies from other countries. Most isolates were serotype 1/2b except for chicken, in which serotype 1/2a was predominant. The serotyping results might imply the presence of food or geography-specific L. monocytogenes strains.     

High incidence of Listeria monocytogenes in European red smear cheese

The incidence of Listeria and Listeria monocytogenes in European red smear cheese was determined in order to assess whether the lack of recent outbreaks of listeriosis associated with cheese is due to improved hygenic conditions in the dairies. Out of European red-smear cheese samples of various types, 15.8% contained organisms of the genus Listeria, 6.4% of the samples were contaminated with L. monocytogenes, 10.6% with L. innocua, and 1.2% with L. seeligeri. Six cheese samples contained two or more Listeria species, including at least one L. monocytogenes isolate. The incidences of L. monocytogenes in cheeses from various countries were: Italy 17.4%, Germany 9.2%, Austria 10%, and France 3.3%. Listeria were found most frequently in soft and semi-soft cheese. Eight samples contained more than 100 L. monocytogenes cfu/cm2 cheese surface, 2 samples had counts above 10(4) cfu/cm2 cheese surface. Surprisingly, a higher incidence of L. monocytogenes was observed in cheeses made from pasteurized milk (8.0%) than in cheeses manufactured from raw milk (4.8%). Phage-typing of isolated Listeria strains clearly confirmed that (i) contaminations within dairy plants were persistent over a period of several weeks to months and (ii) that cross-contamination within the dairy plant is and important factor. Comparison of our data with past surveys seems to indicate that contamination of red smear soft cheese with L. monocytogenes has not decreased sufficiently over the past 15 years. It is therefore strongly recommended that these products are monitored carefully by cheese-making companies.     

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

The aim of this study was to determine the transmission routs of Listeria spp. in dairy farms manufacturing fresh cheese made from ovine and caprine raw milk and to evaluate the impact of Listeria monocytogenes mastitis on raw milk contamination. Overall, 5,799 samples, including 835 environmental samples, 230 milk and milk product samples, and 4,734 aseptic half-udder foremilk samples were collected from 53 dairy farms in the dairy intensive area of Lower Austria. Farms were selected for the study because raw milk was processed to cheese that was sold directly to consumers. A total of 153 samples were positive for Listeria spp., yielding an overall prevalence of 2.6%; L. monocytogenes was found in 0.9% of the samples. Bulk tank milk, cheese, and half-udder samples were negative for Listeria spp. Because none of the sheep and goats tested positive from udder samples, L. monocytogenes mastitis was excluded as a significant source of raw milk contamination. L. monocytogenes was detected at 30.2% of all inspected farms. Swab samples from working boots and fecal samples had a significantly higher overall prevalence (P < 0.001) of L. monocytogenes (15.7 and 13.0%, respectively) than did swab samples from the milk processing environment (7.9%). A significant correlation was found between the prevalence of L. monocytogenes in the animal and in the milk processing environment and the silage feeding practices. Isolation of L. monocytogenes was three to seven times more likely from farms where silage was fed to animals throughout the year than from farms where silage was not fed to the animals.     

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.     

Occurrence of Listeria spp. in critical control points and the environment of Minas Frescal cheese processing

Critical control points (CCPs) associated with Minas Frescal cheese (a Brazilian soft white cheese, eaten fresh) processing in two dairy factories were determined using flow diagrams and microbiological tests for detection of Listeria monocytogenes and other species of Listeria. A total of 218 samples were collected along the production line and environment. The CCPs identified were reception of raw milk, pasteurization, coagulation and storage. Thirteen samples were positive for Listeria; 9 samples were Listeria innocua, 2 were Listeria grayi and 2 were L. monocytogenes. In factory A, Listeria was found in 50% of raw milk samples, 33.3% of curd samples, 16.7% of pasteurized milk samples, 16.7% of cheese samples and 25% of rubber pipes used to transport the whey. The microorganism was not obtained from environmental samples in this plant. In factory B, Listeria was found in one sample of raw milk (16.7%) and in three samples of environment (17.6%) and L. monocytogenes was obtained from raw milk (16.7%) and the floor of the cheese refrigeration room (14.3%). Two serotypes, 4b and 1/2a, were observed among the strains of L. monocytogenes isolated, both which are frequently involved in outbreaks of food-borne listeriosis and sporadic cases of the disease all over the world.     

Detection of Listeria monocytogenes in pigs and pork

In this study, we surveyed hogs (n = 300) as well as pork products (ground pork and raw chitterlings) for Listeria monocytogenes. Pig specimens collected before (tonsil swabs) and after slaughter (tonsils, lymph nodes, carcass swabs, and rectal contents) were examined for L. monocytogenes by enrichment with conventional enrichment broths followed by subculturing to selective agar. A multiplex polymerase chain reaction assay targeting the highly conserved 16S rRNA gene of the Listeria species as well as the hlyA gene unique to L. monocytogenes was used to screen aliquots of the enrichment (method I) as well as to confirm presumptive Listeria colonies from Columbia agar with 0.05% glucose supplemented with polymyxin B-acriflavine-lithium chloride-ceftazidime-aesculin-mannitol (PALCAM; method II). Subculturing to PALCAM agar was the more sensitive of the two methods on the basis of the overall detection of Listeria. For hog tissues, method I detected L. monocytogenes (0.87% positive) and no other Listeria spp. in all samples (n = 1,849). In contrast, method II detected significantly more (P < 0.05) L. monocytogenes (2.38%) and Listeria spp. (0.38%) in these tissues. For small intestines (n = 300 raw chitterlings), L. monocytogenes was identified in 8.3% of enrichments with University of Vermont modified Listeria enrichment broth; plating to PALCAM slightly improved recovery (9%). Overall, ground pork samples (n = 340) harbored L. monocytogenes (45% positive) and other Listeria species (1.5% positive), as determined by method I. Subculturing to PALCAM significantly (P < 0.05) improved the detection of L. monocytogenes (50.2%) but not that of other Listeria species (1.7%). L. monocytogenes isolates (n = 243) were assigned to serotype 1 (53.5%), serotype 4 (25%), and serotypes other than 1 and 4 (21.4%).     

Incidence and characterization of Listeria spp. from foods available in Korea

A total of 410 domestic Korean food samples were analyzed for the presence of Listeria spp. by the conventional U.S. Department of Agriculture protocol, and presumptive strains were identified by morphological, cultural and biochemical tests according to Bergey's manual and confirmed by API-Listeria kit. Among the total 410 food samples, 46 samples (11.2%) were found to be contaminated with Listeria species. Among the 46 strains of Listeria spp. isolates, 8 strains (17.42%) for Listeria monocytogenes, 3 strains (6.5%) for Listeria seeligeri, 33 strains (71.7%) for Listeria innocua, and 2 strains (4.4%) for Listeria welshimeri were identified, respectively. Also, only beef, chicken, pork, frozen foods, and sausage were contaminated with L. monocytogenes, and the other products were free of L. monocytogenes. Of 46 Listeria spp. isolates, L. innocua (71.7%) was the most predominantly isolated in a variety of foods compared to other Listeria spp. An in vitro virulence assay for Listeria spp. using myeloma and hybridoma cells from murine and human sources was performed. The result showed that only L. monocytogenes killed approximately 95 to 100% hybridoma cells after 6 h and the other Listeria species, such as L. innocua, L. seeligeri, and L. welshimeri strains had about 0 to 10% lethal effect on hybridoma cells. Also, an antibiotic susceptibility test showed that Listeria spp. isolates were very susceptible to the antibiotics tested, except for nalidixic acid. Also, serotyping results showed 75% of L. monocytogenes isolates from beef, chicken, and frozen pizza belonged to serotype 1 and 25% from sausage were type 4.     

A BELGIAN SURVEY OF HYGIENE INDICATOR BACTERIA AND PATHOGENIC BACTERIA IN RAW MILK AND DIRECT MARKETING OF RAW MILK FARM PRODUCTS

To monitor the bacteriological quality of raw milk and raw milk farm products, 143 samples of raw farm milk and 100 samples of raw milk farm products, 64 butters, 9 yogurts, 16 cheeses, 7 ice creams and 4 fresh cheeses, produced in Belgium were examined for coliforms, β-glucuronidase positive Escherichia coli, verotoxin producing Escherichia coli O157 , Staphylococcus aureus, Salmonella spp. , Listeria spp. and Listeria monocytogenes. The results were compared with the threshold and maximum values of the EC directive 92/46/EC or the maximum values of the Belgian Order of Council from September 3, 2000. The presence of staphylococcal enterotoxins was investigated on samples with S. aureus counts higher than the legal threshold values mentioned in the EC directive or, if not regulated in the directive, higher than the maximum value mentioned in the Belgian Order of Council. The obtained results for the hygiene-indicators coliforms, β-glucuronidase positive E. coli and S. aureus in the raw milk samples were comparable with most other industrialized countries. Compared to a prevalence of 0.7% and 6.3% for, respectively , E. coli O157 and L. monocytogenes, no Salmonella was found in the 25 g raw milk farm samples. The isolated E. coli O157 strain was confirmed to be verotoxigenic; it was positive for VT2 , eaeA and hly A. In butter not only a prevalence of 18.7% for L. monocytogenes in 25 g was found but also the maximum values for the hygiene-indicators mentioned in the Belgian Order of Council were often exceeded. No significant difference was found between the count of hygiene-indicators and the presence of Listeria spp. as well in raw milk as in raw milk butter. The bacteriological quality of on-farm made raw milk butter suggest that suitable hygienic conditions are not always provided. One of the 7 ice cream samples contained L. monocytogenes in 25 g.     

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).     

Efficacy of direct plating media for recovering Listeria monocytogenes from foods

Studies were done to evaluate 14 direct plating media for their suitability to recover Listeria monocytogenes strain Scott A from pasteurized whole milk, chocolate ice cream mix, Brie cheese and raw cabbage. Healthy cells were inoculated into foods to achieve viable populations of 10(2), 10(4), or 10(6) cells/ml(g). Bind's Acriflavine Agar, Trypaflavine Nalidixic Acid Serum Agar, Listeria Transport Enrichment Agar, Doyle and Schoeni Selective Enrichment Agar (DSSEA) and Modified DSSEA were not suitable for recovering L. monocytogenes from milk and Brie cheese and were therefore not evaluated as direct plating media for recovering the organism from ice cream mix and cabbage. McBride Listeria Agar (MLA), Gum Base Nalidixic Acid Tryptone Soya Agar (GBNTSA), Modified Despierres Agar (MDA) and Modified MLA (MMLA) performed best for recovering all inoculum populations from milk and ice cream mix. Enumeration of L. monocytogenes on several test media was complicated by the growth of large numbers of background microflora present in cabbage and Brie cheese, especially at the lowest test inoculum (10(2)/g). Generally, complete recovery of L. monocytogenes from Brie cheese and cabbage was attained on media when the inoculum population was greater than or equal to 10(4) cells/g. For Brie cheese, MLA, MDA, MMLA and Dominguez Rodriguez Isolation Agar were superior for recovering L. monocytogenes, while GBNTSA, DLEA, MDA and MMLA were best for recovering the organism from cabbage. Results of this experiment indicate that direct-plating procedures, without prior enrichment, can successfully be utilized for recovering L. monocytogenes from foods such as pasteurized milk and ice cream mix which contain low populations of background microflora. However, recovery of L. monocytogenes from foods such as raw cabbage and Brie cheese, which contain high populations of other microorganisms, was not satisfactory using the direct-plating procedures evaluated in this investigation.     

Listeria monocytogenes, Yersinia enterocolitica, and Salmonella in dairy plant environments.

In order to determine the presence of the three environmental pathogens in dairy plants, six milk and four ice cream plants in a three state area were sampled. A total of 353 environmental samples were taken over three replications. Bacterial counts were performed on the environmental samples for chi-square analysis. Salmonella spp. were not isolated from any of the environmental samples. Yersinia enterocolitica was isolated from 6.8% of the environmental samples. Listeria monocytogenes was isolated from 6.5% of the environmental samples. Listeria spp. other than L. monocytogenes were isolated from 9.3% of the environmental samples. The presence of Y. enterocolitica was significantly related to high bacterial counts for six microbiological tests. The presence of L. monocytogenes was not related to high bacterial counts.     

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.     

Incidence and seasonal variation of Listeria species in bulk tank goat's milk

Four hundred and fifty raw goat's milk samples obtained from the bulk tanks of 39 goat farms were analyzed for Listeria spp. over a 1-year period. Modified versions of the U.S. Department of Agriculture Food Safety and Inspection Service (USDA-FSIS) and Food and Drug Administration (FDA) protocols were used for recovery of Listeria. Overall, 35 (7.8%) samples yielded Listeria spp. with Listeria monocytogenes identified in 17 of the 35 (3.8%) Listeria-positive samples. Listeria innocua was detected in 26 (5.8%) samples. Eight milk samples contained both L. monocytogenes and L. innocua. Milk samples from 18 of the 39 (46.2%) farms were positive for Listeria at least once during this 1-year study. The modified USDA-FSIS method, which used Listeria repair broth rather than University of Vermont (UVM) broth for primary enrichment followed by a 4-h nonselective incubation period, yielded more Listeria-positive samples (77.1%) than the FDA method (51.4%). All L. monocytogenes isolates belonged to serotypes 1 (62.6%) or 4 (37.4%). Moreover, five different Listeria ribotypes were identified from 34 selected L. monocytogenes isolates, 2 of which were deemed to be of clinical importance. Listeria isolation rates were markedly higher during winter (14.3%) and spring (10.4%) as compared to autumn (5.3%) and summer (0.9%) with these trends similar to those previously reported for cow's milk.     

Isolation and pulsed-field gel electrophoresis typing of Listeria monocytogenes from modified atmosphere packaged fresh-cut vegetables collected in Ireland

The incidence of Listeria monocytogenes in modified atmosphere packaged fresh-cut fruits and vegetables from chill cabinets of a supermarket in Ireland was investigated over a 2-year period. Overall, 9.58% of fresh-cut produce was contaminated with Listeria spp. Various species of Listeria were isolated from samples, including L. monocytogenes, L. seeligeri, L. innocua, L. welshimeri, and L. ivanovii. No fruit samples contained detectable L. monocytogenes. Overall, a total of 21 L. monocytogenes isolates (2.9% of samples) were recovered from a range of products, including dry coleslaw mix (80% shredded cabbage and 20% shredded carrot), bean sprouts, and leafy vegetables such iceberg, romaine, and radicchio lettuce and mixed salad leaves (curly endive, escarole, and radicchio leaves). Dry coleslaw mix appeared to have the highest incidence of Listeria contamination (20%) compared with other products. Listeria contamination was more frequent (P < 0.05) during the summer and autumn months than during the winter and spring months. The 21 L. monocytogenes isolates were subsequently subtyped by genomic macrorestriction techniques using ApaI with pulsed-field gel electrophoresis (PFGE). PFGE of digested DNA produced bands of 79 to 518 kb. Four PFGE profiles were identified, and approximately 50% of the isolates were associated with profile 1. This study indicates that fresh-cut vegetables packaged under a modified atmosphere can support growth of numerous species of Listeria, including L. monocytogenes.     

HYGIENIC PARAMETERS, TOXINS AND PATHOGEN OCCURRENCE IN RAW MILK CHEESES

In total, 71 samples of retail raw milk cheeses produced or imported in Belgium and samples of Belgian farmhouse cheeses were examined for cotiforms, β-glucuronidase positive Escherichia coli, Escherichia coli O157 , Staphylococcus aureus, Salmonella spp. , Listeria spp. and Listeria monocytogenes. The presence of staphylococcal enterotoxins was investigated on samples with S. aureus counts higher than 10³ cfu/g. The incidence of coliforms, β-glucuronidase positive E. coli and S. aureus was higher in soft than in blue veined, semi-hard, hard and fresh cheeses. Four mold-ripened soft cheeses were positive for E. coli O157. One of the 4 cheeses was positive for verotoxin VT2. Staphylococcal enterotoxins were detected in 1 soft redsmear cheese, which was positive for L. monocytogenes. L. monocytogenes was also detected in one fresh cheese . Salmonella was not detected in any of the 71 raw milk cheeses.     

An outbreak of food-borne listeriosis due to cheese in Japan, during 2001

Food-borne outbreaks caused by Listeria monocytogenes have been recognized in US and European countries. Only sporadic cases, of neonatal listeriosis, have been reported in Japan. Since L. monocytogenes has been often isolated from foods in Japan, food-borne outbreaks potentially could have occurred. In February 2001, L. monocytogenes serotype 1/2b was isolated from a washed-type cheese during routine Listeria monitoring of 123 domestic cheeses. Further samples from products and the environments at the plant that produced the contaminated cheese were examined for L. monocytogenes. L. monocytogenes serotype 1/2b was detected in 15 cheese samples, at most probable number that ranged from <30 to 4.6 x 10(9)/100 g, and in environmental samples. Studies with people who had consumed cheese from the plant revealed 86 persons who had been infected with L. monocytogenes. Thirty-eight of those people had developed clinical symptoms of gastroenteritis or the common cold type after the consumption of cheese. Isolates from those patients exhibited the same serotype, pathogenicity for mice and HeLa cells, DNA fingerprinting patterns and PCR amplification patterns. From the epidemiological and genetic evidence, it appeared that the outbreak was caused by cheese. This is the first documented incidence of food-borne listeriosis in Japan.     

High-pressure processing of Turkish white cheese for microbial inactivation

High-pressure processing (HPP) of Turkish white cheese and reduction of Listeria monocytogenes, total Enterobacteriaceae, total aerobic mesophilic bacteria, total molds and yeasts, total Lactococcus spp., and total Lactobacillus spp. were investigated. Cheese samples were produced from raw milk and pasteurized milk and were inoculated with L. monocytogenes after brining. Both inoculated (ca. 10(7) to 10(8) CFU/g) and noninoculated samples were subjected to HPP in a high-pressure food processor at 50 to 600 MPa for 5 and 10 min at 25 degrees C. Reductions in L. monocytogenes, total aerobic mesophilic bacteria, Lactococcus spp., and Lactobacillus spp. in both pasteurized- and raw-milk cheese samples and reductions in total molds and yeasts and total Enterobacteriaceae counts in raw-milk cheese samples increased with increased pressure (P < or = 0.05). The maximum reduction of the L. monocytogenes count, ca. 4.9 log CFU/g, was obtained at 600 MPa. Because of the highly inhibitory effect of pasteurization, the total molds and yeasts and total Enterobacteriaceae counts for the cheese samples produced from pasteurized milk were below the detection limit both before and after HPP. There was no significant difference in inactivation of L. monocytogenes, total aerobic mesophilic bacteria, Lactococcus spp., and Lactobacillus spp. under the same treatment conditions for the raw milk and pasteurized milk cheeses and for 5- and 10-min treatment times (P > 0.05). No significant change was detected in pH or water activity of the samples before and after HPP. Our findings suggest that HPP can be used effectively to reduce the microbial load in Turkish white cheese.     

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.     

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 of Aeromonas and Listeria spp. in red meat and milk samples in Brisbane, Australia

A total of 150 samples, 50 each of beef, lamb and pork from 10 local retail stores in Brisbane metropolitan area as well as 150 raw bovine bulk milk tank samples obtained from Queensland United Foods (QUF), were examined for the presence of Aeromonas and Listeria spp. over a period of 1 year. Different sets of enrichment and plating media were used to recover the organisms with subsequent identification using conventional biochemical and serotyping techniques. A total of 509 isolates consisting of Aeromonas spp. (350) and Listeria spp. (159) were obtained from 60%, 58%, 74%, 26.6%, 34%, 40%, 30%, 2.6% of samples of beef, Lamb, pork and milk respectively. Motile aeromonads (A. hydrophila, A. sobria, A. caviae) and Listeria innocua were isolated from all kinds of samples whereas L. monocytogenes was only isolated from flesh food. A. hydrophila contributed the largest percentage of the motile aeromonads (60%). The majority of L. monocytogenes cultures were serotype 4.