결핵균 리팜핀 경계성내성 검출을 위한 내성기준농도 비교 평가
Comparative evaluation of critical concentrations for detecting borderline rifampin resistance in Mycobacterium tuberculosis
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배경: 결핵 치료에서 리팜핀 중요성은 매우 크다. 최근 분자 검사기법의 도입으로 리팜핀 신속내성검출이 가능해지면서 기존 감수성검사법과의 결과 불일치가 환자관리에 혼선을 주고 있다. 세계보건기구에서는 리팜핀 내성을 유발하는 rpoB 유전자의 변이를 분석하였고, 경계성 내성(borderline resistance)을 유발하는 일부 변이가 통상 감수성검사에서 검출되지 않는 문제가 확인되었다. 따라서 세계보건기구에서는 Middlebrook 7H10과 BACTEC MGIT에 대한 리팜핀 내성기준농도를 1.0 μg/mL에서 0.5 μg/mL로 낮추었다. 본 연구에서는 내성기준농도 변경이 리팜핀 내성 검출에 대해 미치는 영향을 평가하고자 하였다. 방법: 2021년 5월부터 2022년 5월까지 항결핵제 감수성검사가 의뢰된 균주를 대상으로 하였다. 총3기관이 참여하였으며 서울의과학연구소는 한천비율법을, 삼성서울병원과 분당서울대병원은BACTEC MGIT 960을 이용하여 기존 농도와 변경된 농도에 대해 모두 시험하였다. 불일치를 보이는 균주에 대해 rpoB 유전자 염기서열분석을 시행하여 변이를 확인하였다. 결과: 5연구기간 동안 시행한 감수성검사 중 1,596건(서울의과학연구소: 1,269, 삼성서울병원: 177,분당서울대병원: 150)의 유효한 결과를 확인하였다. 리팜핀 내성은 1.0 μg/mL에서 35건(2.19%),0.5 μg/mL에서 38건(2.38%)에서 검출되었고, 이소니아지드 내성은 158건(9.90%)이었다. 리팜핀 불일치 균주 3건 중 rpoB 유전자 염기서열분석을 통해 H445L 변이가 한 건, 나머지 2건에서는L452P 변이가 확인되었다. 해당변이는 모두 경계성 내성 변이로 분류된다. 결론: 새로 변경된 리팜핀 내성기준농도를 적용할 경우 리팜핀 내성률은 0.19%, 검출건수는8.57% 증가하였다. 또한 다수의 리팜핀 감수성 균주로 평가하였음에도 위내성 결과는 발생하지않았다. 따라서 새로운 내성기준농도를 적용할 경우 내성결핵 관리에 유용할 것으로 판단된다.
Abstract
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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