title: Evaluation of the Etest for detection of tetracycline resistance in Mycoplasma hominis.
abstract: The Etest was compared with microbroth dilution for performing in vitro susceptibility tests in 38 isolates of Mycoplasma hominis chosen to represent a wide range of MIC values. MIC50s were 4 micrograms/ml for both methods; whereas, MIC90s were 64 and > 256 micrograms/ml for broth and Etest, respectively. Etest MICs determined on SP 4 agar were usually two or more dilutions greater than microbroth MICs in SP 4 broth, and values were prone to change by one to two dilutions when different inoculum densities were used. Inocula of 10(5) to 10(6) color-changing units/ml gave the most consistently readable MICs, with discrete colony formation surrounding the ellipse. Etest MICs for 5 isolates tested a second time at the same inoculum on SP 4 agar agreed with the original value within 1 dilution. For 12 isolates tested on A 8 agar simultaneously with SP 4 agar, MICs for 10/12 agreed within one dilution; whereas, in the other 2 isolates, MICs varied by two dilutions. These findings suggest that the Etest, when properly controlled, can be used to determine tetracycline MICs for M. hominis.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham 35233, USA.
authors.forename: K B
authors.initials: KB
authors.lastname: Waites
authors.forename: D M
authors.initials: DM
authors.lastname: Crabb
authors.forename: L B
authors.initials: LB
authors.lastname: Duffy
authors.forename: G H
authors.initials: GH
authors.lastname: Cassell
mesh_terms: D008826:Microbial Sensitivity Tests; D009175:Mycoplasma Infections / Q000188:drug therapy; D019535:Mycoplasma hominis / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D013753:Tetracycline Resistance