A multicenter study evaluating the current strategies for isolating Staphylococcus aureus strains with reduced susceptibility to glycopeptides.
Glycopeptide-intermediate Staphylococcus aureus (GISA) and heterogeneous GISA (hGISA) strains are notoriously difficult to detect in the diagnostic laboratory. The clinical importance of GISA, and particularly hGISA, will only be obvious when a definitive detection method is available. A few novel GISA and hGISA detection methods have been proposed; however, their validity has never been tested on a significant scale and in different laboratories. This study compares three screening methods for detecting GISA and hGISA strains in 12 laboratories, using a blind panel of 48 strains with known glycopeptide susceptibilities. The three screening methods used were brain heart infusion agar with 6 mg/liter vancomycin (BHIA6V) (CDC/CLSI), Mueller-Hinton agar with 5 mg/liter teicoplanin (MHA5T) (European Antimicrobial Resistance Surveillance System [EARSS]), and the macrodilution method Etest (MET) (EARSS), with population analysis profile-area under the curve analysis as the gold standard. Sensitivity and specificity were highest for MHA5T and MET, which identified 82.5% and 85.9% of strains, respectively. BHIA6V had poor sensitivity, particularly for hGISA (11.5% of strains were detected), and gave the largest interlaboratory variation in performance. MET exhibited the least interlaboratory variation. It is essential that laboratories use appropriate methods to detect GISA/hGISA strains so that the prevalence and clinical importance of these strains can be assessed properly.
Wootton
Mandy
M
NPHS Microbiology Cardiff, University Hospital Wales, Cardiff, United Kingdom. mandy.wootton@bristol.ac.uk
MacGowan
Alasdair P
AP
Walsh
Timothy R
TR
Howe
Robin A
RA
D000362:Agar; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015373:Bacterial Typing Techniques / Q000379:methods; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D006020:Glycopeptides / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects*; D017334:Teicoplanin / Q000494:pharmacology; D014640:Vancomycin / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D003470:Culture Media; D006020:Glycopeptides; D017334:Teicoplanin; D014640:Vancomycin; D000362:Agar