Vancomycin reformulation in a Microscan Dried Overnight Panel: a multicentre evaluation with Gram-positive cocci including VRSA

Abstract number: p441

Zimmer  B., Mirrett  S., Reller  L.B., Weinstein  M., Hindler  J., Carey  R., McAllister  S., Bruckner  D., Johnston  J., Sei  K.


Vancomycin-resistant Staphylococcus aureus (VRSA) (MIC >16 mg/ml) were first described in 2002 with four documented VRSA by 2005. Investigations showed inconsistent detection of VRSA by commercial systems including MicroScan panels. This study assessed performance of a revised formulation of vancomycin (Va) on MicroScan Dried Overnight Panels for ability to detect Va resistance in VRSA and other gram-positive cocci (GPC).


Accuracy was evaluated by comparing the test panel to CLSI reference (REF) panel. Strains tested included staphylococci obtained through NARSA (53 strains with reduced susceptibility to Va and 3 VRSA) and 50 Enterococci (CDC challenge set with 25 VRE). An additional 172 isolates of S. agalactiae, S. bovis, and recent Staphylococci and Enterococci were evaluated. All testing included turbidity and Prompt inocula, and three read methods: WalkAway and autoSCAN-4 instruments, and manual. In addition, the three NARSA VRSAs and one additional VRSA were tested at CDC and MicroScan panels read manually.


Testing with revised Va formulation showed 3 VRSA to have MICs >16 mg/ml at 16 h with WalkAway or manual read, and >16 mg/ml at 18 h with the autoSCAN-4. Testing of the fourth VRSA at CDC showed a stably resistant morphotype giving MICs of >16 mg/ml with manual read. Results obtained were equivalent to REF for 100% sensitivity in detection of VRSA isolates. Combined results for all strains tested were >97% in essential agreement and >93% in categorical agreement (M100-S15) with REF. There were no very major or major errors.


The revised formulation of Va on MicroScan Dried Overnight Panels showed excellent sensitivity and specificity. Va resistance was detected in all VRSA available at the time of comparative testing and VRE without overcalling resistance in Va-susceptible GPC.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Location: Oxford, UK
Presentation type:
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