Antimicrobial susceptibility profiles of Staphylococcus aureus isolated in 2007 from French patients with bloodstream infections: goodbye hVISA, welcome Geraldine?

Sir, In France, the high prevalence of oxacillin-resistant Staphylococcus aureus (ORSA) leads to the empirical use of vancomycin in the case of invasive staphylococcal disease.1,2 We previously reported in 2000 the spread of heterogeneous vancomycin-intermediate S. aureus (hVISA) among bacteria implicated in bacteraemia; 8% of the ORSA showed confirmed heteroresistance to glycopeptides, all of them being gentamicin resistant.1 Recently, the increasing prevalence of hVISA and confirmation of their clinical impact were reported.3 These disturbing reports led us to renew a similar study 7 years later in the same network. During October 2007, all non-duplicate isolates of S. aureus from clinically relevant blood culture were collected in 52 non-teaching hospitals belonging to the College of Bacteriology-Virology-Hygiene.1,2 All isolates were sent to a central laboratory (Department of Biology and Infection Control, Hôpital de Dourdan). Antibiotic susceptibility was determined by the disc diffusion method and interpreted according to the guidelines of the Antimicrobial Committee of the French Society of Microbiology. An additional D-zone test was performed to detect inducible clindamycin resistance. S. aureus identification and oxacillin susceptibility were previously confirmed by a specific method.2 As in 2000, hVISA was specifically sought by inoculation of 10 µL of broth culture (turbidity equivalent to that of a 2 McFarland standard) on Mueller–Hinton agar (MHA) plates containing 5 mg/L teicoplanin. Additionally, the Macro Etest® method was performed; vancomycin and teicoplanin Etest® (bioMérieux, France) strips were deposited on MHA plates inoculated with a bacterial suspension (turbidity equivalent to that of a 2 McFarland standard) and a positive result was considered when the MIC reached ≥6 mg/L after a 48 h incubation period. Population analysis of the isolates presenting at least one positive screening test was performed at the National Reference Centre of Staphylococci (Lyon, France). Statistical analysis was performed using the Fisher exact test; a P value of ≤0.05 was considered significant.