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KMID : 1142720230260040139
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Annals of Clinical Microbiology
2023 Volume.26 No. 4 p.139 ~ p.145
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Comparative evaluation of critical concentrations for detecting borderline rifampin resistance in Mycobacterium tuberculosis
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Kim Chang-Ki
Huh Hee-Jae
Park Jeong-Su
Kim Tae-Soung
Sohn Jae-Han
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Abstract
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Background: Rifampin plays an important role in tuberculosis treatment. In recent years,the introduction of molecular testing techniques has enabled the rapid detection ofrifampin resistance, leading to discrepancies with conventional methods. The World HealthOrganization (WHO) has analyzed mutations in the rpoB gene that induce rifampin resistanceand identified certain mutations causing borderline resistance, which are often undetectedusing conventional tests. Consequently, the WHO has lowered the rifampin resistancecriterion concentration from 1.0 to 0.5 μg/mL in 7H10 and MGIT 960. The present study aimedto evaluate the impact of this change in critical concentration on the detection of borderlinerifampin resistance in Mycobacterium tuberculosis.
Methods: Tuberculosis strains submitted for antituberculosis drug susceptibility testing fromMay 2021?2022 were analyzed. Three institutions participated; the Seoul Clinical Laboratoriesused the agar proportion method, whereas the Samsung Medical Center and Seoul NationalUniversity Bundang Hospital utilized the MGIT 960 system to test both the original and revisedconcentrations. Mutations were confirmed through rpoB gene sequencing for strains showingdiscrepancies.
Results: A total of 1,596 valid susceptibility tests were conducted during the study period.
Rifampin resistance was detected in 35 cases (2.19%) at 1.0 μg/mL and in 38 cases (2.38%) at0.5 μg/mL, whereas isoniazid resistance was observed in 158 cases (9.90%). Among the threerifampin discrepancy strains, one harbored an H445L mutation, whereas the remaining twoexhibited an L452P mutation. These mutations were classified as borderline resistant.
Conclusion: Applying the new rifampin critical concentration resulted in a 0.19% increasein resistance rate and an 8.57% increase in detection cases. Additionally, despite testingwith large number of rifampin-susceptible strains, no false resistance results were obtained.
Therefore, the application of the new critical concentration is considered beneficial for themanagement of rifampin-resistant tuberculosis.
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KEYWORD
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Tuberculosis, Rifampin, Borderline resistance
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