Detection of enterococcal high-level aminoglycoside resistance with MicroScan freeze-dried panels containing newly modified medium and Vitek Gram-Positive Susceptibility cards.
Both conventional and modified MicroScan Type 5 panels and Vitek Gram-Positive Susceptibility cards were compared with agar dilution screen plates for their abilities to detect high-level resistance to gentamicin and streptomycin in 235 enterococcal isolates, including 167 Enterococcus faecalis and 63 E. faecium isolates. The modified Type 5 panels contained dextrose-phosphate broth instead of Mueller-Hinton broth in their high-level-resistance screen wells. The sensitivities for detection of gentamicin and streptomycin high-level resistance were 100 and 100% (E. faecalis) and 100 and 94% (E. faecium) for the modified MicroScan panels, 100 and 89% (E. faecalis) and 100 and 98% (E. faecium) for the conventional MicroScan panels, and 81 and 86% (E. faecalis) and 85 and 94% (E. faecium) for the Vitek cards. All specificities were 100% except for the Vitek cards with streptomycin, where it was 96%. Isolates that showed resistance on the streptomycin agar screen plates were rescreened on plates containing 32,000 micrograms/ml to detect ribosomally mediated resistance. For all three systems, every failure to detect streptomycin high-level resistance occurred in isolates with enzymatic, not ribosomal, resistance. The modified MicroScan Type 5 panels are a suitable method for detecting enterococcal high-level resistance to gentamicin and streptomycin. The Vitek cards are too insensitive for this purpose.
Weissmann
D
D
Department of Pathology, Massachusetts General Hospital, Boston 02114.
Spargo
J
J
Wennersten
C
C
Ferraro
M J
MJ
D000617:Aminoglycosides / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D013293:Enterococcus faecalis / Q000187:drug effects / Q000302:isolation & purification; D005069:Evaluation Studies as Topic; D005839:Gentamicins / Q000494:pharmacology; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000295:instrumentation*; D012680:Sensitivity and Specificity; D013045:Species Specificity; D013291:Streptococcus / Q000187:drug effects* / Q000302:isolation & purification; D013307:Streptomycin / Q000494:pharmacology
D000617:Aminoglycosides; D005839:Gentamicins; D013307:Streptomycin