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.

Species identification, slime production and oxacillin susceptibility in coagulase-negative staphylococci isolated from nosocomial specimens

Ninety-two coagulase negative staphylococci (CNS) (forty-five of clinical origin and forty-seven of environmental origin), collected in a hospital in San Luis, Argentina, from March to June, 1999, were identified to species level by the ID 32 Staph and API Staph System (bioMérieux). Slime production was investigated by the quantitative and qualitative methods. Oxacillin susceptibility was determined by the disk diffusion test (1 µg), the agar dilution method (0.125 to 4 mg/ml) and agar screen (6 µg/ml). The presence of mecA gene was investigated by PCR. The clinical CNS species most commonly isolated were S. epidermidis, S. haemolyticus, S. hominis and S. saprophyticus. The frequency of slime production by clinical and environmental isolates was similar (25/45 and 27/47, respectively) and the results obtained by the quantitative and the qualitative methods correlated well. The mecA gene was detected in all S. epidermidis, S. haemolyticus and S. hominis isolates, which were resistant to oxacillin by the phenotypic methods. However, this gene was not present in S. klossii, S. equorum, S. xylosus and S. capitis strains. The gene was neither found in two out of the six S. saprophyticus isolates, in two out of three S. cohnii subsp. urealyticum isolates and in two out of five S. cohnii subsp. cohnii isolates, all of which resulted oxacillin resistant according to MIC. The gene was not found in oxacillin-susceptible strains either. Most of the CNS isolates (enviromental and clinical) that were slime producers were found to be oxacillin resistant, which makes the early detection of these microorganisms necessary to prevent their dissemination in hospitals, particularly among immunocompromised patients.

Noventa e duas amostras de Staphylococcus coagulase negativo (SCN), (45 amostras clínicas e 47 ambientais), coletadas em um hospital de San Luis, Argentina, durante o período de março a junho de 1999, foram identificadas até espécies, empregando-se os sistemas ID 32 Staph e API Staph (bioMérieux). A produção de "slime" foi investigada através de métodos quantitativo e qualitativo. A susceptibilidade à oxacilina foi determinada por métodos de difusão em discos (1 µg), diluição em ágar (0,125 a 4 mg/ml) e ágar screen (6 µg/ml). A presença do gene mecA foi pesquisada por PCR. As espécies de SCN de origem clínica mais comumente isoladas foram S. epidermidis, S.saprophyticus, S.hominis e S.haemolyticus. Observou-se uma freqüência similar na produção de "slime" nas amostras de origem clínica e ambiental (25/45 e 27/47, respectivamente), tendo havido concordância nos resultados obtidos pelos métodos quantitativo e qualitativo. O gene mecA foi observado em todas as cepas de S. epidermidis, S. haemolyticus e S. hominis que foram resistentes a oxacilina pelos métodos fenotípicos, mas não foi detectado em S. klossii, S. equorum, S. xylosus e S. capitis. O gene também não foi detectado em duas das seis amostras de S.saprophyticus, duas das três S. conhii subsp. urealyticum e duas das cinco S. conhii subsp. conhii, as quais resultaram resistentes à oxacilina segundo a CIM. Esse gene não foi encontrado nas cepas sensíveis à oxacilina. A maioria das amostras de SCN (ambientais e clínicas) que foram produtoras de slime foram resistentes à oxacilina, o que obriga a uma detecção precisa desses microorganismos e ao controle de sua disseminação em hospitais, particularmente entre pacientes imunocomprometidos.