Community acquisition of gentamicin-sensitive methicillin-resistant Staphylococcus aureus in southeast Queensland, Australia

Abstract

Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) susceptible to gentamicin has been reported in a number of countries in the 1990s. To study the acquisition of gentamicin-sensitive MRSA (GS-MRSA) in southeast Queensland and the relatedness of GS-MRSA to other strains of MRSA, 35 cases of infection due to GS-MRSA from October 1997 through September 1998 were examined retrospectively to determine the mode of acquisition and risk factors for MRSA acquisition. Thirty-one isolates from the cases were examined using a variety of methods (antibiotyping, phage typing, pulsed-field gel electrophoresis [PFGE] fingerprinting, and coagulase typing by restriction analysis of PCR products) and were compared with strains of local hospital-acquired gentamicin-resistant MRSA (GR-MRSA) and of Western Australian MRSA (WA-MRSA). Only 6 of 23 cases of community-acquired GS-MRSA had risk factors for MRSA acquisition. Twenty of 21 isolates from cases of community-acquired infection were found to be related by PFGE and coagulase typing and had similar phage typing patterns. Hospital- and nursing home-acquired GS-MRSA strains were genetically and phenotypically diverse. Community-acquired GS-MRSA strains were not related to nosocomial GR-MRSA or WA-MRSA, but phage typing results suggest that they are related to GS-MRSA previously reported in New Zealand.

FIG. 1

Electrophoresis of PCR coagulase gene products and HaeIII-digested products of representative strains. (A) Lanes 1 and 6, size markers; lanes 2 to 5, products A to D, respectively. (B) Lanes 1 and 5, size markers; lanes 2 to 4, RFLP patterns BIII, BII, and AI, respectively. (C) Lanes 1 and 15, size markers, lanes 2 to 14, RFLP patterns AIII, AI, AV, AI, BIV, AIV, AII, C, BI, AII, BI, AI, and AI, respectively.

FIG. 2

Schematic representation of PFGE pulsotypes of 31 study isolates (lanes 1 to 31), 6 nosocomial GR MRSA isolates (lanes 31 to 37), and 2 WA-MRSA isolates (lanes 38 and 39), together with a dendrogram showing percent similarities of patterns and nomenclature of pulsotypes. Letters, pulsotypes (seven or greater band differences); numerals, subtypes (one to six band differences).