Prevalence and Characterization of Heterogeneous Vancomycin-Intermediate Staphylococcus aureus Isolates from 14 Cities in China

Abstract

The prevalence of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) among 1,012 vancomycin-susceptible methicillin (meticillin)-resistant S. aureus isolates collected from 14 cities in China from 2005 to 2007 was 13 to 16%, as determined by a combination of (i) measurement by the modified population analysis profile-area under the curve method (PAP-AUC) and (ii) estimation from the measured sensitivity and specificity of a screening method. Two hundred isolates from blood were chosen as a subset for measurement of the sensitivities and the specificities of several previously described screening methods by using the results of PAP-AUC as the reference. During this testing, one isolate was found to be a vancomycinintermediate S. aureus (VISA) strain so was not used in the evaluation of the screening tests. Of the other 199 isolates, 26 (13.1%) were hVISA, as assessed by PAP-AUC. A screening cascade of culturing the isolates on brain heart infusion agar containing teicoplanin (5 mg/liter) and then subjecting the positive isolates to a macro-Etest method was applied to the 812 non-blood isolates, yielding 149 positive results. From these results and by adjusting for sensitivity (0.423) and specificity (0.861), the prevalence was estimated to be 15.7%. The precision of that estimate was assessed by reapplying the screening cascade to 120 randomly selected isolates from the 812 non-blood isolates and simultaneously determining their heterogeneous vancomycin-intermediate susceptibility status by PAP-AUC. Because PAP-AUC is impractical for use with large numbers of isolates, the screening-based estimation method is useful as a first approximation of the prevalence of hVISA. Of the 27 VISA or hVISA isolates from blood, 22.2% and 74.1% were staphylococcal chromosome cassette mec types II and III, respectively, while 77.8% and 22.2% were agr type 1 and agr type 2, respectively; the MIC ranges were 0.5 to 4 mg/liter for vancomycin and 0.25 to 1 mg/liter for daptomycin.

First Detection of an Invasive Staphylococcus aureus Strain (D958) with Reduced Susceptibility to Glycopeptides in Saudi Arabia

“…Several studies showed that the surveillance of hVISA was not performed routinely and that the methods used differed between laboratories, thus preventing Currently, hVISA isolates are more frequently reported than previously thought. In a recent prospective study performed in France, the prevalence of hVISA was 11% (22), which is similar to previous reports (47,54) from other geographic locations. In Saudi Arabia, hVISA infection was never reported in the past, and its clinical significance appears therefore difficult to assess.…”

Performance of Various Testing Methodologies for Detection of Heteroresistant Vancomycin-Intermediate Staphylococcus aureus in Bloodstream Isolates

“…Reasons for these differences are unclear and may reflect specific MRSA subtype characteristics. However, recent MET and GRD Etest assessments performed on consecutive clinical isolates showed significantly lower sensitivities (44% to 69%) and specificities (48% to 98%) (1,17,18) than those in previous laboratorycharacterized evaluations. This suggests that some of these differences may reflect hVISA phenotype instability (22).…”

Antimicrobial Heteroresistance: an Emerging Field in Need of Clarity

“…A modified PAP assay comparing the area under the curve (PAP-AUC) of a given strain to that of a reference heteroresistant strain was used to determine S. aureus heteroresistance to vancomycin (67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81). PAP-AUC ratios between the test and control strains of Ͻ0.9, 0.9 to 1.3, and Ͼ1.3 were considered indicative of vancomycin-susceptible S. aureus, heterogeneous vancomycinintermediate S. aureus (hVISA), and vancomycin-intermediate S. aureus (VISA), respectively (67,72,74,76).…”