Isolates of methicillin-resistant Staphylococcus aureus (MRSA) not belonging to the Brazilian epidemic clone

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of healthcare-associated infections. Isolates of MRSA not belonging to the Brazilian Epidemic Clone (BEC) are colonizing and infecting patients at the hospital. These include strains carrying SCCmec type II, not previously described in the city of São Paulo, showing a trend to a MRSA genetic diversity. SCCmec typing revealed that Brazilian clone isolates harbor SCCmec III. We found that is possible a MRSA genetic diversity in Brazil, when strains of MRSA not belonging to the Brazilian Epidemic Clone (BEC) that were isolated in patients at the hospital. Note Methicillin-resistant Staphylococcus aureus (MRSA) is involved in increasing number of serious infectious with high risk for morbidity and mortality and it is an important cause of healthcare-associated infections [1]. Although the active surveillance and the impact of MRSA colonization on the occurrence of S. aureus infections are unclear, some studies described that asymptomatic colonization with MRSA is a risk factor for in a subsequent MRSA infection patients [2, 3]. In Brazil, a considerable number of hospital infections have been caused by an unique multi-resistant MRSA clone designated as the Brazilian epidemic clone (BEC) [4]. SCCmec typing revealed that Brazilian clone isolates harbor SCCmec III [5]. During a study on hand hygiene compliance, samples were obtained by nasal swab every four days from 446 patients admitted patients at two step-down units (SDUs) of a private tertiary care hospital in São Paulo, Brazil. Blood Culture samples were also obtained at an intensive care unit (ICU) of the same hospital, as part of an anti-microbial resistance surveillance project (unpublished data). The study period was from March 20, 2007 to Sep-tember 20, 2007 [6]. The open model ICU is a 38-bed medical-surgical unit; where approximately 2,200 patients are admitted annually and the SDUs are medical-surgical 20-bed units each. Nasal samples were plated onto chro-magar (CHROMagar, MRSA, CHROMagar, Paris, France) and selective staphylococcal media (Mannitol Salt Agar). Blood cultures were performed at BACTEC 9240 instrument (BACTEC 9240, BD Diagnostics, Sparks, MD) and the positive samples were plated onto chocolate and sheep blood agar. Twenty-one MRSA strains were isolated from nasal carriers (in the SDUs) and two MRSA strains obtained from patients with bloodstream infections (in the ICU). Staphylococcus species were confirmed by an automated (Vitek 2 System,, Hazelwood, MO)) and manual biochemical tests. For the susceptibility profile determination oxacillin agar screening was used with automated system according with Clinical Laboratory Standards Institute (CLSI) recommendations [7].