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.

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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.

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The natural products derived from medicinal plants have proven to be an abundant source of compounds with antibacterial activity. The antibacterial activity of extracts of Azorella trifurcata and M. echegarayii was evaluated against strains of Staphylococcus aureus ATCC 43300, Pseudomonas aeruginosa ATCC 27853, Listeria monocytogenes CLIP 74902 and Escherichia coli ATCC 35218. Organic extracts were prepared using n-hexane, mixtures of n-hexane and ethyl acetate of increasing polarity and a mixture of ethyl acetate and methanol on flash chromatography. All the extracts of A. trifurcata showed antibacterial effects against grampositive bacteria (CIM between 0.5 and 2 mg/ml). Four extracts (100% n-hexane, 40:60/50:50 acetate: nhexane, 70:30 ethyl acetate: n-hexane and 2:98 methanol: ethyl acetate) of A. trifurcata showed antibacterial activity against gram-negative bacteria. M. echegarayii 2:98 methanol: ethyl acetate was active against all gram-negative and gram-positive bacteria (CIM between 1 and 2 mg/ml). The values of MBC of the extracts assayed were one or two times higher than corresponding MIC values. The discovery of organics extracts with antibacterial properties could contribute to the treatment of bacterial infections.