Abstract
Meticillin-resistant Staphylococcus aureus (MRSA) strains producing the potent tissue necrotizing toxin Panton–Valentine leukocidin (PVL) encoded by the pvl gene, and harbouring SCCmec type IV or V elements, have been implicated as being associated with MRSA infection acquired in the community setting (Vandenesch et al., 2003; Boyle-Vavra & Daum, 2007). Since the 1990s, community-associated (CA)-MRSA infections have shown a steady increase, and are becoming a significant public-health concern. PVL-positive MRSA isolates have been shown to have distinct genetic backgrounds in different areas, for instance, multilocus sequence typing (MLST) types ST80, ST8 and ST59 were found in the major clones in Europe, USA and Taiwan, respectively (Vandenesch et al., 2003; Tristan et al., 2007; Chen et al., 2005).
In Hong Kong, CA-MRSA infection is a notifiable disease, defined by clinical and epidemiological criteria (Millar et al., 2007), together with molecular characterization of the strain, as belonging to SCCmec type IV or V, and being pvl-positive (CHP, 2008). In an attempt to understand the characteristics and epidemiology of pvl-positive MRSA strains in the community in Hong Kong, we characterized 140 CA-MRSA strains isolated in 2006. Our laboratory is a diagnostic and public health laboratory processing clinical specimens from outpatients and hospital inpatients from both the public and private sector. We also serve as a referral centre for characterization of isolates from other laboratories. For any isolate suspected to be CA-MRSA based on clinical and epidemiological grounds, investigations undertaken included antibiogram determination by the disc diffusion method (CLSI, 2005), SCCmec typing (Okuma et al., 2002; Ito et al., 2004) and pvl PCR (Lina et al., 1999). Isolates found to be pvl-positive were further subjected to molecular typing studies, including spa typing (Shopsin et al., 1999) using the Ridom SpaServer, MLST (Enright et al., 2000) and PFGE (McDougal et al., 2003).
One hundred and forty putative CA-MRSA isolates from unique patients were examined during 2006. Forty-two isolates (30 %) were found to carry pvl. Among these, SCCmec IV and V elements were found in 30 (71.4 %) and 12 (28.6 %) isolates, respectively; no other SCCmec element was found in this collection (Table 1). This is in accordance with other reports (Tristan et al., 2007; Boyle-Vavra & Daum, 2007) that pvl carriage is much more frequently associated with SCCmec types IV and V than other types (I, II or III) in S. aureus. In Hong Kong, pvl-positive SCCmec type V isolates have been reported in five MRSA strains (Ho et al., 2007). Our results confirmed the previous findings at an extended scale.