Background: The purposes of the current study were to evaluate the concordant rates of anti-mycobacterial drug susceptibility test (DST) results in different solid media performed in different institutes, and to determine reliable susceptible testing methods.
Methods: One hundred and twenty two Mycobacterium tuberculosis strains were isolated from patients in A Hospital in 2005. DSTs were performed by the absolute concentration method using Lowenstein Jensen medium in both A Hospital (method A-1) and B Institute (method B-1) and by the proportion method using Middlebrook 7H10 agar in B Institute (method B-2). Nine drugs were used including isoniazid and rifampin. Sensitivity and specificity of each method were estimated by using the acceptable standard of 90% for isoniazid and rifampin and 80% for other drugs. The therapeutic outcomes of quinolone-administered patients were evaluated according to ofloxacin susceptibility results.
Results: Method B-1 showed sensitivity and specificity levels over the acceptable standard levels for all drugs. Method B-2 showed specificity lower than the acceptable levels for rifampin and cycloserine.Method A-1 showed specificity lower than the acceptable levels for isoniazid, streptomycin, p-aminosalicylic acid, and ofloxacin and sensitivity lower than the acceptable levels for prothionamide and cycloserine. The concordance rates of therapeutic outcomes with method B-1, method B-2, and method A-1 were 77%, 74%, and 65%, respectively.
Conclusion: The drug susceptibility results for some drugs were discordant between the testing laboratories and media, requiring an urgent application of quality control programs to raise the reliability of anti-mycobacterial DST. (Korean J Clin Microbiol 2008;11:43-48)
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