Heteroresistance to glycopeptides in Italian meticillin-resistant Staphylococcus aureus (MRSA) isolates.

The prevalence and molecular characterisation of heteroresistant vancomycin-intermediate Staphylococcus aureus (hVISA) strains were determined in a large group of Italian strains isolated between 2005 and mid 2007. Amongst the 1284 strains isolated from documented infections in hospitalised patients (bloodstream infection, pneumonia, and skin and skin-structure infections), 139 S. aureus with vancomycin minimum inhibitory concentrations (MICs) between 1 mg/L and 2 mg/L were screened for the presence of hVISA using three different methods and were confirmed by population analysis profile (PAP). Thirty-six hVISA strains (25.9%) were detected. Amongst the three screening methods used, the macro Etest (MET) demonstrated 100% specificity and 75% sensitivity. hVISA strains were accessory gene regulator (agr) types I and II and belonged to the major nosocomial clones circulating in Italy (ST8, ST239, ST247 and ST228). All strains were susceptible to quinupristin/dalfopristin, linezolid, daptomycin, tigecycline and dalbavancin. In conclusion, we have demonstrated that hVISA isolates are common amongst MRSA isolates with MICs between 1 mg/L and 2 mg/L in Italy. MET, with its high sensitivity and specificity, should be used for early detection of hVISA, especially in patients with serious or prolonged infections sustained by MRSA. Finally, the most recent anti-Gram-positive drugs maintained their full spectrum of in vitro activity against these strains.

Staphylococcus haemolyticus endocarditis: clinical and microbiologic analysis of 4 cases.

Only 3 cases of infective endocarditis (IE) due to methicillin-resistant Staphylococcus haemolyticus (MRSH) have been reported in English literature. Here we report 4 cases of IE due to MRSH encountered in a single university hospital. Population analysis of the strains was performed to assess the presence of vancomycin/teicoplanin heteroresistant subpopulations. Pulsed-field gel electrophoresis was used for molecular typing of isolates. IE was defined in 3 cases as health care associated, and in 1 case, as community acquired. A causative strain was lost. Two strains were heteroresistant to teicoplanin, and 1 also to vancomycin. Genome macrorestriction profile studies demonstrated that 2 MRSH isolates belonged to clones A and E, possessing a class C1 mecDNA, whereas 1 clone was sporadic. All patients were treated with vancomycin plus rifampin. Two patients were cured with antibiotic therapy alone, 1 patient needed surgery, and 1 patient died. Methicillin-resistant multiresistant S. haemolyticus may represent a difficult-to-treat cause of both community and nosocomially acquired IE.