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Volume 7, Number 2—April 2001
4th Decennial International Conference on Nosocomial and Healthcare-Associated Infections

State of the Art

Increasing Resistance to Vancomycin and Other Glycopeptides in Staphylococcus aureus

Fred C. Tenover*, James W. Biddle*, and Michael V. Lancaster†
Author affiliations: *Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †Bright Ideas, Monterey, California, USA

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Table 2

Key techniques for recognizing glycopeptide-intermediate Staphylococcus aureus strainsa

Technique Results Comment
Broth microdilutionb Vancomycin MIC = 8-16 µg/mL in Mueller-Hinton broth Hold test for full 24 hours
Brain heart infusion agar containing 6 µg/mL of vancomycin obtained from a commercial sourcec Growth in 24 hours One or more colonies is a positive result; use S. aureus ATCC 25923 as negative control, and Enterococcus faecalis ATCC51299 as positive control
Etest Vancomycin MIC > 6 µg/mL on Mueller-Hinton agar Hold test for full 24 hour

aAll three criteria must be met before an organism is defined as a glycopeptide-intermediate S. aureus. bCDC uses inhouse-prepared MIC plates; however, any full dilution range broth microdilution plates, such as MicroScan conventional panels or PASCO frozen MIC panels, if incubated at 35C for a full 24 hours, can be used. cSee reference 34 for explanation.

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