Presence of enterotoxigenic Staphylococcus aureus in artisan fruit salads in the city of San Luis, Argentina

An increase in the consumption of fruit juices and minimally processed fruits salads has been observed in recent years all over the world. In this work, the microbiological quality of artisan fruit salads was analysed. Faecal coliforms, Salmonella spp, Shigella spp, Yersinia enterocolitica and Escherichia coli O157:H7 were not detected; nevertheless, eleven strains of Staphylococcus aureus were isolated. By multiplex PCR, all isolates showed positive results for S. aureus 16S rRNA gene and 63.6% of them were positive for sea gene. Furthermore, PCR sea positive strains were able to produce the corresponding enterotoxin. Finally, the inactivation of these strains in fruit salads by nisin, lysozyme and EDTA, was studied. EDTA produced a total S. aureus growth inhibition after 60 h of incubation at a concentration of 250 mg/L. The presence of S. aureus might indicate inadequate hygiene conditions during salad elaboration; however, the enterotoxigenicity of the strains isolated in this study, highlights the risk of consumers' intoxication. EDTA could be used to inhibit the growth of S. aureus in artisan fruit salads and extend the shelf life of these products.

Presence of enterotoxigenic Staphylococcus aureus in artisan fruit salads in the city of San Luis, Argentina.

An increase in the consumption of fruit juices and minimally processed fruits salads has been observed in recent years all over the world. In this work, the microbiological quality of artisan fruit salads was analysed. Faecal coliforms, Salmonella spp, Shigella spp, Yersinia enterocolitica and Escherichia coli O157:H7 were not detected; nevertheless, eleven strains of Staphylococcus aureus were isolated. By multiplex PCR, all isolates showed positive results for S. aureus 16S rRNA gene and 63.6% of them were positive for sea gene. Furthermore, PCR sea positive strains were able to produce the corresponding enterotoxin. Finally, the inactivation of these strains in fruit salads by nisin, lysozyme and EDTA, was studied. EDTA produced a total S. aureus growth inhibition after 60 h of incubation at a concentration of 250 mg/L. The presence of S. aureus might indicate inadequate hygiene conditions during salad elaboration; however, the enterotoxigenicity of the strains isolated in this study, highlights the risk of consumers' intoxication. EDTA could be used to inhibit the growth of S. aureus in artisan fruit salads and extend the shelf life of these products.

Detection of Yersinia spp. in meat products by enrichment culture, immunomagnetic separation and nested PCR.

The prevalence of Yersinia enterocolitica in meat products was assessed by four methods: cold enrichment in trypticase soy broth (A), enrichment in modified Rappaport broth at 25 °C (B), concentration by immunomagnetic separation (C) and yadA nested PCR (D). Furthermore, the pathogenic potentials of the isolates were established by phenotypic and genotypic tests, and their genomic relationships were determined by pulsed-field gel electrophoresis (PFGE). A total of 238 samples were collected at retail level in the city of San Luis, Argentina, during the period 2007-2008. The highest Yersinia prevalence in meat products was observed by method D (92 positive samples), followed by methods A (13 positive samples) and C (5 positive samples); however, no isolation was obtained by method B. Fourteen Y. enterocolitica and 4 Yersinia intermedia strains were recovered by culture. All Y. enterocolitica 2/O:9 strains gave results related to virulence by phenotypic tests and exhibited the genotype virF(+)myfA(+)ail(+)ystA(+). Two biotype 1A strains showed a genotype virF(-)myfA(-)ail(+)ystA(+)ystB(+). The 14 Y. enterocolitica strains isolated during this work plus one reference strain were separated into 11 genomic types by PFGE. This genomic heterogeneity of the isolates shows the diversity of Y. enterocolitica strains in our region. It is the first time that IMS was used to search Y. enterocolitica strains from naturally contaminated meat products.

Pulsed field, PCR ribotyping and multiplex PCR analysis of Yersinia enterocolitica strains isolated from meat food in San Luis Argentina.

The characterization of phenotypic and genotypic virulence markers of Yersinia enterocolitica strains belonging to biotypes (B) 1A, 2 and 3, mostly isolated from food in San Luis, Argentina, and the assessment of their genotypic diversity using PFGE and PCR ribotyping, were performed in our laboratory for the first time. Thirty five Y. enterocolitica strains, two reference strains and 33 strains isolated in our laboratory were studied. The presence of virF, ail, ystA, and myfA genes was investigated by multiplex PCR. The pathogenic potential of B1A strains, the most predominant biotype of Y. enterocolitica strains isolated from meat in our region, was investigated by simple PCR. Four B1A strains were positive for ystB gene. Four Y. enterocolitica 2/O:9 (bio/serotype) and two 3/O:5 strains isolated in our laboratory showed virulence-related results in the phenotypic tests and multiplex PCR. A good correlation between the expression of virulence markers and their corresponding genotypes was observed for most strains. Sixteen genomic types (GT) and 9 different intergenic spacer region (SR) groups were generated by PFGE and PCR ribotyping, respectively. In both cases the Y. enterocolitica 2/O:9 strains were separately clustered from 1A and 3/O:5 strains. Meat foods might be vehicles of transmission of pathogenic Y. enterocolitica strains in our region.

Survival of Aeromonas hydrophila in Fresh Tomatoes ( Lycopersicum esculentum Mili) Stored at Different Temperatures and Treated with Chlorine.

This study examines the survival of two Aeromonas hydrophila strains ( A. hydrophila ATCC 7965 [strain A] and A. hydrophila isolated from food [strain B]) on the surface and core tissue of fresh tomatoes stored at different temperatures and the efficacy of chlorine treatment on their survival. Counts of A. hydrophila on the surface of tomatoes stored at 25 and 35 °C were significantly higher between days 1 and 4 for both strains as compared to results obtained at 6°C. Core tissue counts of A. hydrophila cells on tomatoes dipped in a cellular suspension at 25°C and stored at 25°C were significantly higher (P < 0.05) than counts obtained with dip suspensions at 6 or 35°C. In chopped tomatoes stored at 25 and 35°C, populations of aerobic mesophiles showed significant increases after 96 and 70 h, respectively. The populations of both A. hydrophila strains in chopped tomatoes stored at 6°C increased significantly after 96 h, while at 25 and 35°C the counts increased in the first hours of incubation. Viable counts of A. hydrophila on the surface and central tissue of tomatoes significantly decreased (P < 0.05) when the samples were dipped for 2 min in chlorine at a concentration of 50 ppm (50 µg/ml). The results suggest that tomatoes should be kept at low temperatures during storage, shipping, and retail stocking and that chlorine at a concentration of 50 ppm should be used to reduce the levels of A. hydrophila .

Prevalence of Yersinia enterocolitica in Hake (Merluccius hubbsi) Fillets.

Yersinia enterocolitica is a human pathogenic bacterium. The prevalence of Y. enterocolitica in refrigerated hake fillets sold for human consumption in retail stores was investigated in order to determine the degree of pathogenicity. Three hundred samples were enriched in 0.067 M phosphate-buffered saline, pH 7.6, with 1% sorbitol and 0.15% biliary salts, postenriched in 0.5% KOH, and isolated in salmonella-shigella agar and MacConkey agar. Twelve strains of Yersinia were isolated from the whole group of samples, 11 (91.6%) of which corresponded to Y. enterocolitica and 1 (8.3%) to Y. intermedia . The Yersinia strains recovered were Y. enterocolitica B1 O:5 Lis Xz (1 strain), Y. enterocolitica B3 O:5 (1 strain), Y. enterocolitica B1 O:6,30-6,31 (1 strain), Y. enterocolitica B1 O:7,8-8-8,19 (1 strain), Y. enterocolitica B1 O:7,8-8-8,19 Lis Xz (7 strains) and Y. intermedia B1 O:40 Lis Xo (1 strain). Of the 12 strains isolated, 8 (66.6%) were recovered by alkaline postenrichment. The first two strains were positive for virulence tests (autoagglutination and calcium dependence for growth at 37°C). The antibiotic susceptibility of the isolated strains was studied by the agar-diffusion method according to Bauer-Kirby, modified by Barry. Some of the isolated strains were potentially pathogenic, representing a risk for human health.

Biovars, Serovars, and Phagovars of Yersinia enterocolitica Isolated From 450 Samples of Cold Food in San Luis, Argentina.

A search of Yersinia enterocolitica in foods of animal origin has been carried out. Isolates were obtained from 450 samples of cold foods: 100 samples of cooked ham, 150 samples of salami, 100 samples of porcine cheese (artisan cold foods), and 100 samples of mortadella. Enrichments were performed in 0.067 M phosphate buffered saline solutions, pH 7. 6, containing 1% sorbitol and 0.15% biliary salts. The samples were postenriched in 0.5% KOH. Subcultures were done in Salmonella-Shigella agar and MacConkey agar. Isolates were identified through biochemical, serological, and phagotyping methods. The following biovars (B), serovars (O), and phagovars (Lis) were isolated from cooked ham B2 0:9 Lis X3 (1%), from salami B1 0:5 Lis Xz and B2 0:9 Lis X3 (1.33%), from porcine cheese B2 0:9 Lis X3 (2%), and from mortadella (0%). Virulence tests (calcium dependent growth at 37°C and autoagglutination activity at 37°C) were always negative. Serovar B2 0:9 Lis X3 associated with human disease was isolated. It is concluded from the results of this study that Y. enterocolitica isolates from cold foods lack of pathogenic importance.