VITEK GPS CARD SUSCEPTIBILITY TESTING ACCURACY USING DIRECT INOCULATION FROM BACTEC-9240 BLOOD CULTURE BOTTLES

The emergent need for antimicrobial susceptibility testing (AST) data for the therapy of bacteremic patients has led to the development of r apid methods and local procedure modification of some commercial AST p roducts such as the direct inoculation from blood culture systems. We compared the Vitek GPS card results using direct and standardized inoc ulation with a reference broth microdilution method for 112 consecutiv e staphylococcal bloodstream infections (Seven drugs). Among the 28 St aphylococcus aureus strains, 0%-3.6% total error/drug was observed wit h both Vitek inoculation procedures. However, the only oxacillin-resis tant strain was not detected (100% true very-major error). For 84 coag ulase-negative staphylococci (CNS), the direct inoculation procedure h ad an 11.9% very-major error rate for oxacillin, ampicillin-sulbactam, and cephalothin, plus 4.8% very-major error rate for ciprofloxacin an d trimethoprim-sulfamethoxazole (total error rate 4.8%-16.7% for five of seven drugs compared). The Vitek direct inoculation procedure routi nely missed 20.4% of oxacillin-resistant CNS strains. The use of Vitek direct inoculation procedures for staphylococcal bloodstream infectio n isolates (from BACTEC 9240 cultures) produced serious false-suscepti ble results; this procedure should be avoided in favor of routine pack age insert-recommended Vitek procedures or other reference-quality ove rnight incubation susceptibility tests.