Genotipos de Staphylococcus aureus con fenotipo meticilino resistente, aislados de pacientes del Hospital Base de Valdivia / Genotypes of Staphylococcus aureus strains with methicillin resistant phenotype

ABSTRACT

Background: Methicillin resistant strains of Staphylococcus aureus (MRSA) are an important cause of nosocomial infections. Aim: To determine the genotypes of MRSA strains. Material and methods: Fifty five strains of MRSA, isolated from patients hospitalized in Hospital Base Valdivia, were studied. The phenotype was determined through MicroScan® in all strains and by minimum inhibitory concentration (MIC) in 41. The genotype of the strains was analyzed by a duplex polymerase chain reaction (PCR) of the mecA gene, amplifying eight hypervariable DNA regions associated to such gene. Results: According to MIC, 88 percent of strains had a pattern of resistance against multiple antimicrobial (penicillin, ampicillin, cephradine, gentamycin, ciprofloxacin, íincomycin and erythromycin). Vancomicin resistan strains were not detected. Only 53 strains (96 percent) had at least one of the eight hypervariable regions and were classified as MRSA. Genotypic patterns types 15 were the most commonly detected in 38 percent and 34 percent of strains, respectively. MicroScan® erroneously classified five strains in an incorrect phenotype, according to results obtained with duplex PCR. MIC results did not differ from those of duplex PCR. Conclusions: Duplex- PCR is a useful tool to detect hyper variable regions associated to mecA gene.