Prevalence of methicillin-resistant Staphylococcus aureus with reduced susceptibility to glycopeptides in Belgian hospitals: results of a multicentre survey

Abstract number: 1733_1323

Glupczynski Y., Behrin C., Allemeersch D., André M., De Beenhouwer H., Cartuyvels R., Frans J., Govaerts D., Joseph R., Phillipart I., Surmont I., Van den Abeele A-M., Verhaegen J., Nonhoff C., Denis O., Struelens M.

Objectives: MRSA isolates with decreased susceptibility to glycopeptides (GISA/h-GISA) have been reported worldwide. Several studies have shown that such strains could be associated with a poor clinical outcome. The aim of the present study was to determine the prevalence of GISA/h-GISA strains among Belgian MRSA isolates collected from hospitalised patients.

Methods: Consecutive non duplicate MRSA clinical isolates prospectively collected between 01/2005 and 07/2005 in 13 hospitals were screened locally for reduced susceptibility to glycopeptides by the modified Macromethod Etest according to Walsh et al. (JCM 2001) and by teicoplanin (5 mg/L) agar screen (TAS). Etest MICs of both vancomycin (VA) and teicoplanin (TP) ≥ 8 mg/L or of TP alone >12 mg/L and growth on TAS were indicative of potential GISA/h-GISA or of hetero-teicoplanin intermediate S. aureus (h-TISA). All suspected strains were sent to the reference laboratory for confirmation by Etest MIC determination on MH agar as well as by VA and TP population analysis profiles (PAP). Confirmed GISA/h-GISA isolates were also analysed by PFGE in order to delineate their clonality.

Results: Of 573 MRSA strains tested (mean number of isolates by centre: 44; range: 30–54), 31 (5.4%) met the phenotype screen criteria of GISA/h-GISA. Putative GISA strains were found in 10 of the 13 participating labs and their frequency by centre ranged between 0 and 13%. 24 isolates (4.2%) were confirmed as h-TISA and 2 (0.3%) as GISA or h-GISA by MIC testing (VA MIC of 4 and 8 mg/L) and by PAPs. Origins of the isolates were: lower respiratory tract (11), wounds (7), blood (4) and urine (2). Fourteen of the 24 h-TISA strains were resistant to gentamicin by disk diffusion. By molecular analysis, all h-TISA isolates clustered in two epidemic PFGE groups (A and D) which were previously reported in h-GISA or in h-TISA isolates in Belgium. The two GISA strains were clearly unrelated to each other and to the h-TISA strains. Dissemination of h-TISA isolates belonging to the same clone resulted in small local outbreaks in six of the centres.

Conclusion: Overall GISA/h-GISA isolates were found in 4.5% of the Belgian MRSA isolates from hospitalised patients. Most of the isolates had a h-TISA phenotype. Although uncommon, the occurrence of GISA/h-GISA among MRSA strains is higher than reported previously in other surveys in Belgium and could possibly be attributed to the spread of certain epidemic clones within and across hospitals.