2415. Comparison of Minocycline MIC’s Obtained by Etest to Those Obtained by Broth Microdilution in a Bank of Isolates of Acinetobacter baumannii Collected in Southeastern Michigan

Abstract

BackgroundMinocycline is an important antibacterial for the management of AB infections. Discordance in tigecycline susceptibilities between BMD and ET has been as high as 43% (a ≥log 2 dilution higher MIC by ET). As many automated susceptibility panels do not include minocycline clinicians must rely on ET results. This analysis assesses the discordance between methodologies for minocycline and compares activity of minocycline and tigecycline against a clinical set of AB isolates from Southeast Michigan.MethodsTesting using BMD and ET were done on 386 isolates of AB from 5 hospitals. Results were compared using FDA breakpoints with BMD considered the gold-standard. Correlations were defined as: (i) essential agreement (EA) if the ET MIC was identical to or 1 doubling dilution from the BMD MIC, (ii) categorical agreement (CA) if results via BMD and ET were the same susceptibility category, (iii) minor error if the isolate was intermediate by either test, but either susceptible or resistant by the other test, (iv) a major error if the isolate was false resistant by ET, and (v) a very major error if ET was false susceptible. Comparative BMD susceptibility between tigecycline and minocycline was also assessed.ResultsOf the 386 isolates of AB, 87% were susceptible to minocycline by BMD and 77% by ET (9.6% difference, P < 0.001). MIC comparisons are shown in Table 1. EA occurred in 80% of isolates and CA in 87%. Discordant results included 47 minor errors, 11 major errors, and 0 very major errors. 14% of isolates had >1 double dilution difference between the methodologies and 4% had >2 double dilution differences. Susceptibility rates to tigecycline and minocycline were both 87%, with 11% of tigecycline nonsusceptible isolates susceptible to minocycline and 4% of minocycline nonsusceptible isolates susceptible to tigecycline.ConclusionMinocycline provides excellent activity against AB. ET provides reliable susceptibility results in comparison to BMD.Table 1:Minocycline Susceptibility Comparing ET vs. BMDET, n (%)BMD, n (%)MIC≤0.250.51248>8>800000018(4.7%)800002(0.5%)13(3.4%)17 4.4%)42 (0.5%)01(0.25%)3 (0.8%)5(1.3%)10(2.6%)7(1.8%)201(0.25%)2 (0.5%)33 (8.5%)15(1.3%)11(2.8%)2(0.5%)102 (0.5%)14(3.6%)78(20.2%)20(5.2%)7 (1.8%)2 (0.5%)0.51(0.25%)6 (1.6%)14(3.6%)6(1.6%)000≤0.2578(20.2%)9 (2.3%)5 (1.3%)2(0.5%)000Disclosures K. Kaye, Zavante Therapeutics, Inc.: Scientific Advisor, Consulting fee.