Analysis of the genetic diversity of vancomycin-resistant Staphylococcus aureus

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin- resistant coagulase-negative staphylococci (MRCoNS) are among the most frequent causes of hospital infections worldwide, thus justifying the increasing use of vancomycin. In this study, we evaluated the presence of glycopeptide-resistant staphylococci, in 41 patients hospitalized in the Clinical Hospital of the Federal University of Uberlândia in Uberlândia, MG, who were being treated with vancomycin. All isolates were plated on Mueller-Hinton agar containing vancomycin. Vancomycin resistance was confirmed by surface growth after incubation for 24-48 h at 35°C. Heteroresistance was evaluated by plating with a large inoculum (108 CFU/mL). One patient with nephritis who was on a hemodialysis program was diagnosed with the phenotype isolate of vancomycin-intermediate Staphylococcus aureus (VISA) (CIM = 8 μg/mL) and in eight patients, strains of heteroresistant Staphylococcus corresponding to the hVISA phenotype were isolated. In addition to the extended use of vancomycin, other risk factors associated with the presence of these microorganisms included the use of three or more antimicrobial agents, surgery, and three or more invasive procedures. Molecular analysis by randon amplified polymorphic DNA - polymerase chain reaction (RAPD-PCR) showed two clusters involving two samples each one of them, in surgical patients, with temporal and spatial relationship and isolates similarity concerning the susceptibility range to antimicrobial agents.