Epidemiologia molecolare di batteriemie da Staphylococcus aureus meticillino-resistente in nord-Italia

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.