Minocycline Susceptibility and tetB Gene in Carbapenem-Resistant Acinetobacter baumannii in Taiwan

Abstract

Purpose: In this study, we evaluated the minocycline susceptibility rate in carbapenem-resistant Acinetobacter baumannii (CRAB) clinical strains, and the association between tetB carriage and minocycline susceptibility in CRAB.

Patients and methods: A total of 100 genetically unrelated CRAB clinical strains from bloodstream infection were randomly collected from a medical center in Taiwan. An argument for a new minocycline susceptibility breakpoint of 1 mg/L was suggested based on pharmacokinetic (PK) and pharmacodynamic (PD) studies. Strains with minocycline minimum inhibitory concentrations (MICs) of >1 mg/L were classified as PK-PD non-susceptible. TetB carriage was detected by polymerase chain reaction (PCR).

Results: Fifty-five (55%) CRAB strains were susceptible to minocycline according to the Clinical and Laboratory Standards Institute (CLSI) criteria, among which 98.2% (54/55) were PK-PD non-susceptible. The minocycline MIC_50/90 was 4/16 mg/L. Ninety-seven (97%) strains carried tetB. All of the tetB-positive strains and 66.7% (2/3) of the tetB-negative strains were PK-PD non-susceptible. By statistical analysis, tetB carriage was significantly correlated with PK-PD non-susceptibility (P = 0.03) and a higher minocycline MIC (P = 0.02). The sensitivity and specificity of the tetB PCR for predicting PK-PD non-susceptibility were 98% and 100%, respectively.

Conclusion: At our institute, most CRAB strains were PK-PD non-susceptible and most carried tetB gene. Recognizing the minocycline MIC and tetB status may be essential when using minocycline to treat CRAB-related infections.

Keywords: CRAB; efflux; minocycline PK-PD non-susceptibility; multidrug resistance.

Figure 1

Distribution of minocycline minimum inhibitory concentrations (MICs) of the 100 carbapenem-resistant Acinetobacter baumannii strains.