Characterization of Staphylococcus aureus strains isolated from humans in Argentina.

Humans are a natural reservoir of Staphylococcus aureus and asymptomatic colonization is far more common than infection. The aim of this work was to characterize genotypically 68 S. aureus strains isolated from nasal swabs of healthy people and from human clinical infections. A total of fourteen (20%) strains were susceptible to all the antimicrobials tested. The strains isolated from nasal swabs showed the lowest percentages of resistance. Resistance to one or more than one antibiotics tested was detected in 83% and 70% of the S. aureus strains isolated from clinical infections and nasal swabs, respectively. All of the 68 S. aureus strains were subject to RAPD-PCR analysis. Cluster A-I grouped 42 (87%) clinical infection strains and cluster A-II grouped 13 (65%) strains isolated from nasal swabs suggesting a genetic relationship among S. aureus strains. Cluster A-II grouped 65% of the S. aureus strains associated with the anterior nares, suggesting that these strains may be adapted to this site. Furthermore, five RAPD profiles isolated from nasal swabs, belonged to clusters B to F, were similar to strains isolated from clinical infection, suggesting that they might have a high propensity to cause disease. The results of the present study allow a characterization of S. aureus strains isolated from humans and shows that some S. aureus genotypes from nasal swabs are similar to the genotypes obtained from clinical infections, suggesting that clinical isolates may be originated from human normal flora.