Low prevalence of methicillin-resistant Staphylococcus aureus with reduced susceptibility to glycopeptides in Belgian hospitals

Abstract

Staphylococcus aureus strains with decreased susceptibility to glycopeptides (GISA) have been associated with increased risk of glycopeptide treatment failure. To assess the prevalence of these strains in hospitalised patients in Belgium, 455 methicillin-resistant S. aureus (MRSA) isolates collected in 2001 were screened by two assays: (i) growth on vancomycin agar screen (VAS; brain heart infusion agar (BHI) + vancomycin 6 mg/L); and (ii) a synergy/antagonism test with aztreonam/cefazolin on Mu3 agar (BHI + vancomycin 3 mg/mL). Isolates growing on VAS or Mu3 agar were characterised further by analysis of population susceptibility profiles. MICs of glycopeptides were determined by agar dilution, broth microdilution and Etest (low and high inocula) methods. The isolates were genotyped by pulsed-field gel electrophoresis (PFGE) and determination of staphylococcal cassette chromosome mec (SCCmec) type. No GISA isolates were found. Three (0.7%) hetero-vancomycin intermediate S. aureus (hVISA) and ten (2.2%) hetero-teicoplanin intermediate S. aureus (hTISA) isolates were identified by population analysis. All but one hetero-GISA isolate belonged to either epidemic PFGE group A/SCCmec type I (69%) or PFGE group D/SCCmec type I (23%), both of which were resistant to gentamicin. The sensitivity and specificity for the detection of hetero-GISA by the two assays were 15.4% and 99.8%, respectively, for VAS, and 84.6% and 95.9%, respectively, for Mu3. The data indicated that hetero-GISA strains were uncommon among Belgian MRSA isolates from hospitalised patients. Use of Mu3 agar was more sensitive, but less specific, than VAS as a screening method.

Reduced Vancomycin Susceptibility inStaphylococcus aureus, Including Vancomycin-Intermediate and Heterogeneous Vancomycin-Intermediate Strains: Resistance Mechanisms, Laboratory Detection, and Clinical Implications

“…A study of MRSA isolates from 63 French hospitals found that only 0.7% of isolates were hVISA isolates after screening with BHI agar containing 6 g teicoplanin per ml and confirmation by PAP (37), with similarly low rates found by some other French studies and in Belgium (69,230,271). However, a subsequent study at one French institution, which screened 2,300 S. aureus isolates using BHIA with 4 g teicoplanin per ml, followed by MET and then PAP confirmation, found that 11% of the isolates were hVISA isolates, which were found to be clonal by pulsed-field gel electrophoresis (93).…”

Investigation of Reduced Susceptibility to Glycopeptides among Methicillin-Resistant Staphylococcus aureus Isolates from Patients in Ireland and Evaluation of Agar Screening Methods for Detection of Heterogeneously Glycopeptide-Intermediate S. aureus

“…The criterion used to define hGISA was any isolate recovered by any screening method with a vPAP-AUC ratio of 0.9 to 1.29 and/or a tPAP with a resistant subpopulation growing at concentrations Ͼ8 mg of teicoplanin/liter (18,29).…”

“…Volumes (50 l) were inoculated onto BHI agar plates containing 0, 0. (18,29). After 48 h of incubation at 35°C, the colonies were counted, and the log of the CFU/ml was plotted against the antibiotic concentration by using GraphPad Prism software (GraphPad Software, Inc., San Diego, CA) to obtain vancomycin PAPs (vPAP) and teicoplanin PAPs (tPAP).…”

“…The vPAP-AUC ratio criteria were as follows: glycopeptide-susceptible S. aureus (GSSA), Ͻ0.9; hGISA, 0.9 to 1.29; and GISA, Ն1.3. The criterion to define hTISA isolates using tPAP was any isolate with a resistant subpopulation that grew at concentrations above the susceptible breakpoint (Ͼ8 mg of teicoplanin/ liter) (18). PAPs were performed on all isolates with Etest macromethod values of Ն8 mg/liter for both vancomycin and teicoplanin or Ն12 mg/liter for teicoplanin alone (n ϭ 139).…”

Molecular characteristic of Staphylococcus aureus isolates in a Chinese teaching hospital

“…In this study, 9 out of 156 MRSA isolates (5.9%) were identified as hVISA by MET. In USA, Italy, Canada, France, Israel, Belgium and Asia, the prevalence of hVISA in MRSA was 7.5, 2.8, 1.3, 0.21, 6, 0.7 and 4.3% (Rybak et al, 2008;Campanile et al, 2010;Adam et al, 2010;Reverdy et al, 2001;Maor et al, 2007;Nonhoff et al, 2005;Song et al, 2004), respectively. The disparity in the prevalence of hVISA in different areas may be due to the different detection methods, geographical differences and variable incidence.…”