Healthcare associated PVL negative methicillin-resistant Staphylococcus aureus with SCCmec type IV.

To the Editors: Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are on the rise in many regions of the world. In Brazil, CA-MRSA is still uncommon and MRSA are mostly associated with hospital acquired infections. We have observed a shift in the antimicrobial susceptibility patterns of MRSA isolates at our hospital from conventional multiresistance to resistance primarily against erythromycin. The aim of our study was to characterize recent MRSA isolates from pediatric patients at our institution for the staphylococcal cassette chromosome (SCC) mec types and the presence of the Panton-Valentine leukocidin (PVL) genes, and to evaluate the genetic relatedness of isolates by pulsed-field gel electrophoresis (PFGE). We hypothesized that the hospital acquired isolates would have SCCmec and PFGE types usually associated with community acquired isolates, thus indicating an influx of CA isolates into our hospital. Methicillin-resistant S. aureus isolates were identified and collected between May 2004 and June 2007. Antimicrobial susceptibility tests were performed by diskdiffusion, according to Clinical and Laboratory Standards Institute recommendations. Isolates were classified as CA or HCA based on published criteria. This study was approved by the Ethics Committee at Santa Casa de São Paulo. The isolates were tested for the presence of the PVL genes (lukF-PV and lukS-PV), SCCmec was typed by polymerase chain reaction and PFGE was performed, as previously described. Twenty-nine nonconsecutive pediatric isolates of methicillin-resistant S. aureus from 29 hospitalized patients were studied. Infections included bloodstream (BSI), (6) septic arthritis (2), pneumonia (4), and abscesses (2). Eight isolates were obtained from catheter tips of patients with signs and symptoms consistent with BSI, however, peripheral blood cultures were not available for analysis. Seven isolates were from surveillance cultures. One of the 29 isolates had SCCmec type I, 3 type II, 13 type III, 11 type IV and one was nontypeable. No single source was associated with a particular SCCmec type or PFGE pattern. SCCmec type IV MRSA isolates were found among both clinical and surveillance cultures. PFGE comparisons grouped 8 of the 11 SCCmec type IV isolates in one cluster of related banding patterns. Nine of 13 SCCmec III isolates were related. All other SCCmec I-IV isolates had unrelated banding patterns (Figure, Supplemental Digital Content 1, http://links.lww.com/INF/A156). Only 2 of 29 isolates were considered CA. One of these isolates, containing SCCmec type IV, was from a previously healthy 26-day-old who presented with septic arthritis of the right wrist on admission and the infection was ruled CA. The second CA isolate, with nontypeable SCCmec, was obtained from a previously healthy 10-yearold girl without HCA risk factors who was diagnosed with multifocal septic arthritis. In addition, this was the only isolate that carried the PVL genes. All the other 28 isolates were PVL-negative. The nontypeable SCCmec and the SCCmec type IV isolates were resistant only to penicillin, oxacillin, and erythromycin. They were all D-test negative. All other MRSA isolates were multiresistant to penicillin, oxacillin, erythromycin chloramphenicol, ciprofloxacin, gentamycin, trimethoprim-sulfamethoxazole, clindamycin and variably resistant to tetracycline. All isolates were susceptible to vancomycin. Little is known about the overall burden and the molecular characteristics of CA-MRSA in South America. In Brazil, community acquired MRSA infection rates remain low although CA-MRSA was reported first in 2005. By PFGE, the SCCmec III cluster in our study showed relatedness to the ST239 clone, previously identified as a nosocomial pathogen in our area. The SCCmec IV cluster had PFGE patterns similar, but not identical to, nosocomial BSI isolates reported previously in São Paulo. These strains have no resemblance to widespread CA clones such as OSPC or USA300 and contrary to these clones, our SCCmec type IV strains were all negative for the PVL genes. It is intriguing that this strain cluster established itself in the hospital without being associated with wide-spread community-acquired disease as has been observed for SCCmec type IV strains elsewhere. A better understanding of the clinical implications, pathogenic and transmission potential of this novel SCCmec type IV clone requires evaluation in a larger, prospective study. Comparisons of the Brazilian SCCmec type IV isolates to successful community-acquired SCCmec type IV clones may reveal factors that are important for S. aureus isolates to successfully be established in the community.