Community acquired methicillin-resistant staphylococcus aureus: is an Italian emergence?

Introduction Methicillin-resistant Staphylococcus aureus (MRSA) emerged as a cause of hospital infection in 1961, only two years after the introduction of methicillin. In Italy the rate of MRSA in hospital is very high (39-41%) and it is stable since many years. In the last years, there have been several reports of community-acquired MRSA (CA-MRSA) which differ from hospital-acquired MRSA strains (HA-MRSA) for a susceptibility profile with resistance to fewer classes of antibiotics and for the presence of specific virulence factors such as the Panton-Valentine Leukocidin toxin. Moreover CA-MRSA were found to contain SCCmec type IV or V. Objectives The aim of this study was to investigate if CAMRSA strains were present in Italy since they have been detected not only in North America, but also in Europe; second, to examine these strains both epidemiologically and microbiologically; third, to establish any clonal relatedness in order to compare CA-MRSA clones circulating in Italy to those distributed world-wide. Methods In the period April 2005-March 2007 six strains of CAMRSA were obtained from two different geographycal areas: Center and North Italy. Antibiotic susceptibility patterns were performed by automatyzed system. The presence of mecA/nuc (methicillin resistance and species identification, respectively) and lukS-PV−lukF-PV [Panton-Valentine Leucocidin (PVL) toxin] genes was assayed by PCR. Characterisation of the structural type of the Staphylococcal chromosomal cassette mec (SCCmec) was performed by multiplex PCR. The genetic background was studied by pulsed field gel electrophoresis (PFGE); any distinct profile was defined as a pulsotype. The repeat region of the S. aureus protein A (spa) gene was sequenced. Multilocus sequence typing (MLST) was performed by PCR amplification of internal fragments of seven housekeeping genes to characterise the clonal group. Results All the six isolates were confirmed as MRSA. Al l the strains were susceptible to non β-lactam antibiotics; out of six strains five were susceptible to fusidic acid and one was fully resistant. Out of six strains five carried class B mecA gene complex. In five isolates the type IV of the mec element was detected. One strain harbour the SCCmec type V. All strains showed the presence of PVL. By PFGE four different pulsotypes were identified (A, B, C, D) . By spa typing, three isolates were assigned to novel spa type (755 ,1552 and 2453) as well as in three strains spa type 008 was indicated. By MLST isolates were assigned to four different clones (ST30, ST8, ST80 and STnew). Conclusions Most CA-MRSA strains circulating in Italy belong to those clones prevalent both in Europe and US; they are characterised by the same phenotypical and genotypical characteristics. The cases described probably represent the tip of an iceberg because of there are, probably, many undetected cases. The most dreadful trend is represented by the introduction of these virulent strains in the hospital, where there are many vulnerable patients. Using appropriate infection control measures it should be possible to contrast these pathogens both in community and in the clinical settings to limit their worldwide spread.