Antibiogram as instrument of phenotypic typing of Staphylococcus aureus isolated from personnel, raw milk and minas frescal cheese in a dairy plant of Goiás, Brazil

Abstract

During a year (March/2004 to February/2005) 140 samples of raw milk, dairy staff, and Minas Frescal cheese were analyzed for the presence of S. aureus in a dairy plant in Goiás, Brazil. Strains were isolated from 75% of the personnel investigated resulting in 31 (33.7%) isolates from 92 collected samples (46 from hands and 46 from nasopharynx). The 24 raw milk samples resulted in 18 (75.0%) positive samples and 26 isolates, with mean number: 1.1 x 10(5) CFU/ml. Among 24 cheese samples 17 (70.8%) were positive resulting in 20 isolates, with mean number: 3.8 x 104 CFU/g. Thirteen samples (54.2%) were above the limit established by the brazilian legislation (10³ CFU/g). The differentiation of strains was performed by antimicrobial susceptibility test. All isolates were susceptible to ciprofloxacin and gentamicin. Resistance was observed in five (6.5%) isolates for erythromycin, 19 (24.7%) for tetracycline, one (1.3%) for vancomycin, four (5.2%) for oxacillin and 53 (68.8%) isolates for penicillin. Eleven isolates (14.3%) were susceptible to all antibiotics tested and 18 (23.4%) were resistant to more than one antibiotic. The antibiotic susceptibility allowed the discrimination of isolates in 12 different profiles (A-L), but the phenotypic typing failed to determine the source of bacteria for the cheese.