Staphylococcus aureus in a northern Italian region: phenotypic and molecular characterization

Staphylococcus aureus is a leading cause of community-acquired infections and healthcare-associated infections. Epidemiological data are useful for understanding the dynamics of the diffusion of this pathogen, and to plan control activities and monitor their efficacy.

S. aureus isolates were collected in 13 public hospital laboratories of Emilia-Romagna (northern Italy region) during February-March 2009; phenotypic and molecular characterizations of these isolates were performed.

The study sample included 267 isolates, 57 from blood, 81 from respiratory tract, and 129 from wounds; 106 (40%) were methicillin-resistant S. aureus (MRSA). MRSA showed a limited number of circulating clones with 2 predominant spa types--t008 and t041--accounting for 36% and 27% of MRSA isolates, respectively. The t041 type had a higher prevalence of antimicrobial resistance compared to other spa types and accounted for most of the retrieved hetero-vancomycin-intermediate S. aureus (h-VISA), while t008 was more frequently detected in non-hospital isolates. A higher degree of genetic diversity was observed in methicillin-susceptible S. aureus (MSSA), with no predominant clones and low prevalence of antimicrobial resistance. The occurrence of community-acquired MRSA infection appears to be rare in Emilia-Romagna.

In contrast to previous studies reporting Italian data, t008 was the most frequent spa type among MRSA isolates in Emilia-Romagna. The prevalence of antimicrobial resistance of different MRSA spa types could influence their ability to cause infections with hospital onset. The presence of only 2 major MRSA clones circulating in Emilia-Romagna increases the chances that a regional strategy aimed at MRSA prevention will be effective.