Molecular epidemiology of methicillin-resistant Staphylococcus aureus from bacteraemia in northern Italy.

BACKGROUND

Vancomycin is frequently used in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia; reduced susceptibility to vancomycin is therefore disturbing.

METHODS

molecular epidemiological analysis of 81 MRSA bacteraemia isolates collected during 2002-10 in the province of Bolzano, northern Italy was performed. MICs of a range of antimicrobials were determined by agar microdilution, screening for hGISA was by Macro-Etest and Etest GRD and confirmed by PAP-AUC with vancomycin and teicoplanin. All isolates were characterised by toxin gene profiling, agr, spa, and SCCmec-typing; MLST and PFGE were carried out on representative strains.

RESULTS

The dominant clones identified were ST8-MRSA-IVc (55%) and ST228- and ST111-MRSA-I (25%); most of the latter two lineages (19/20; 95%) were GISA or PAP-AUC confirmed hGISA. One ST8-MRSA-IVc isolate harboured ccrA2B2 together with ccrA4B4. The remainder were diverse genotypically and belonged to MLST clonal complexes 1, 22, 45 and 398.

CONCLUSIONS

Diverse lineages of MRSA were identified as causing bacteraemia in a province in northern Italy. The association of a specific genotype with the hGISA and GISA phenotypes among representatives of the second most common lineage identified is of clinical concern.