Moodley V.M., Oliver S.P., Shankland I., Elisha B.G.
Division of Medical Microbiology, Clinical Laboratory Sciences, University of Cape Town, Cape Town, South Africa; Groote Schuur Hospital, National Health Laboratory Services (NHLS), Cape Town, South Africa
Moodley, V.M., Division of Medical Microbiology, Clinical Laboratory Sciences, University of Cape Town, Cape Town, South Africa, Groote Schuur Hospital, National Health Laboratory Services (NHLS), Cape Town, South Africa; Oliver, S.P., Division of Medical Microbiology, Clinical Laboratory Sciences, University of Cape Town, Cape Town, South Africa, Groote Schuur Hospital, National Health Laboratory Services (NHLS), Cape Town, South Africa; Shankland, I., Groote Schuur Hospital, National Health Laboratory Services (NHLS), Cape Town, South Africa; Elisha, B.G., Division of Medical Microbiology, Clinical Laboratory Sciences, University of Cape Town, Cape Town, South Africa, Groote Schuur Hospital, National Health Laboratory Services (NHLS), Cape Town, South Africa
Acinetobacter baumannii is a major nosocomial pathogen causing infections in critically ill patients. This organism has acquired the propensity to rapidly develop resistance to most antibiotics. At several hospitals within Cape Town, South Africa, tobramycin and colistin are frequently the only therapeutic options. Vitek2 automated susceptibility testing (AST) is used in the clinical laboratory to determine selected susceptibility profiles. The suspicion of a possible AST-related technical error when testing for susceptibility to tobramycin in A. baumannii precipitated this study. Thirty-nine A. baumannii strains isolated from clinical specimens (June to December 2006) were included in this prospective study. Tobramycin susceptibility testing results obtained by AST, disc diffusion, the epsilometer test (Etest), and agar dilution were compared to those for broth microdilution (BMD), the reference method. The tobramycin susceptibility results revealed errors in 25/39 (64%) isolates (10 very major and 15 minor errors) when AST was compared to BMD, 12/39 (31%) (2 very major and 10 minor errors) when Etest was compared to BMD, 16/39 (41%) (3 very major and 13 minor errors) when disc diffusion was compared to BMD, and 21/39 (54%) (10 very major and 11 minor errors) when agar dilution was compared to BMD. Using PCR, we detected aac(3)-IIa, which is associated with tobramycin resistance, in 21/25 of the discrepant isolates. Molecular typing (using pulsed-field gel electrophoresis and repetitive sequence-based PCR [rep-PCR]) showed that these isolates were genetically related. Clinical laboratories that routinely use the Vitek2 system should consider an alternative testing method for determining susceptibility to tobramycin. Copyright © 2013, American Society for Microbiology.
tobramycin; aac(3) IIa gene; Acinetobacter baumannii; agar dilution; analytical error; antibiotic resistance; article; bacterial gene; bacterial strain; broth dilution; controlled study; disk diffusion; epsilometer test; gene cluster; human; intermethod comparison; laboratory automation; minimum inhibitory concentration; molecular epidemiology; molecular typing; nonhuman; nucleotide sequence; polymerase chain reaction; priority journal; prospective study; pulsed field gel electrophoresis; Acinetobacter baumannii; Acinetobacter Infections; Anti-Bacterial Agents; Diagnostic Errors; Drug Resistance, Bacterial; Humans; Microbial Sensitivity Tests; South Africa; Tobramycin