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 35ºC. Heteroresistance was evaluated by plating with a large inoculum (10 8 CFU/mL). One patient with nephritis who was on a hemodialysis program was diagnosed with the phenotype isolate of vancomycinintermediate 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.

Genetic similarity between staphylococcus sp isolated from human and hospital settings, and susceptibility to different antimicrobials

“…In our work, isolation frequency of Staphylococcus sp resistant to oxacillin (42%), was lower than that found in another study developed (22), in a hospital in the city of Uberlândia, Brazil (78%). Nevertheless, although lower, such level can also cause worry, since oxacillin-resistant microorganisms are considered to be resistant to all β-lactamic antimicrobials (6,24).…”

Epidemiology of meticillin-resistant Staphylococcus aureus (MRSA) in Latin America

“…Between 1997 and 1999, 93.3% of S. aureus isolates in bloodstream infections in a newborn unit in Rio de Janeiro, Brazil, were meticillin-resistant [17]. Of note, Melo et al [25] found that in Uberlândia, Brazil, 9 of 41 patients receiving treatment with vancomycin were infected with MRSA isolates that met criteria for heteroresistance to vancomycin, and one of the isolates had a MIC of 8 g/mL. In a large teaching hospital in Lima, Peru, 85% of 73 hospital-acquired S. aureus infections were reported to be due to MRSA in 2002 [19].…”

Occurrence of the vanA gene in Staphylococcus epidermidis from nasopharyngeal secretion of Health-Care Workers, Recife, Brazil

“…In 2006, three strains were reported, two S. aureus and one CoNS, with resistance to both antibiotics vancomycin and methicillin 45 . A potential emergence of vancomycin resistance may occur in hospitals in Brazil, as reported in recent studies 9,28 . This suggests the need for constant monitoring of susceptibility patterns to vancomycin, application of molecular methods and heteroresistance detection, as well as adoption of control measures to avoid the spread of these strains in the hospital environment.…”

“…In Brazil, staphylococcal strains with reduced susceptibility to glycopeptides were reported in hospitals in São Paulo and Rio de Janeiro a decade ago 9 , and recently S. aureus containing the vanA and vanB genes were described in Brazil 10,11 . Colonization of diverse body sites by CoNS, and transient colonization by S. aureus, can be a source of infection for immunocompromised patients 12 , highlighting microbiota colonization of health professionals as a source of dissemination of health care-associated infections (HAIs) 13 .…”