特定のgyrA遺伝子変異は，中国北京から分離されたMycobacterium tuberculosis分離株における不一致レボフロキサシン耐性の高い有病率と相関していた

Specific gyrA gene mutations correlate with high prevalence of discordant levofloxacin resistance in Mycobacterium tuberculosis isolates from Beijing, China.

• Fengmin Huo
• Yifeng Ma
• Shanshan Li
• Yi Xue
• Yuanyuan Shang
• Lingling Dong
• Yunxu Li
• Yu Pang

抄録

迅速かつ高感度な分子診断検査はフルオロキノロン（FQ）耐性結核（TB）の診断に有用であるが，分子検査と従来の逐次的表現型薬剤感受性検査（pDST）の結果はしばしば不一致を示す。ここでは、2018年1月～12月に中国・北京で採取した臨床結核分離株のMeltPro TB分子検査対pDSTで得られたレボフロキサシン（LFX）耐性の結果の不一致率を測定した。不一致の結果が得られた単離株は、不一致の原因を探るために、さらにLFX最小阻害濃度（MIC）決定およびDNA配列解析を行った。全結核症例571例のうち、126/571例（22.1％）がMeltPro TBアッセイを用いてLFX耐性であることが確認された。しかし，LFX耐性株126株のうち34株がpDST法でLFX感受性と判定され，不一致率は27.0％であった。LFXのMICは主に臨界濃度付近に集中しており，MICは7株（21.2％）が2.0 mg/L，13株（39.4％）が4.0 mg/Lであった。LFX耐性菌の中で最も頻度が高かったのは，DNAジラーゼサブユニットAのアミノ酸置換基Ala90Val（13株，39.4％）およびAsp94Ala（11株，33.3％）であり，MICは7株（21.2％），13株（39.4％）であった。特に，MeltPro法でLFX耐性と判定された分離株の4分の1以上がpDST法でLFX感受性と判定された．最終的に，LFX耐性試験の結果は，MICが臨界LFX濃度に近づいた分離株の特異的なgyrA遺伝子変異と関連していた．

Although rapid, highly sensitive molecular diagnostics tests are useful for diagnosing fluoroquinolone (FQ)-resistant tuberculosis (TB), results of molecular testing versus conventional sequential phenotypic drug susceptibility testing (pDST) are frequently discordant. Here we determined the discordance rate of levofloxacin (LFX) resistance results obtained via MeltPro TB molecular testing versus pDST of clinical TB isolates collected in Beijing, China between January and December 2018. Isolates with discordant results were further subjected to LFX minimal inhibitory concentration (MIC) determinations and DNA sequence analysis to explore causes of discordance. Of 571 total TB cases, 126/571 (22.1%) were identified as LFX-resistant using the MeltPro TB assay. However, 34 of these 126 LFX-resistant isolates yielded LFX-susceptible test results using pDST, for an overall discordance rate of 27.0%. LFX MICs mainly clustered around the critical LFX concentration, with 7 (21.2%) and 13 (39.4%) isolates exhibiting MICs of 2.0 mg/L and 4.0 mg/L, respectively. The most prevalent LFX resistance mutations associated with discordant results involved in DNA gyrase subunit A amino acid substitutions Ala90Val (13, 39.4%) and Asp94Ala (11, 33.3%). Notably, more than one quarter of isolates deemed LFX-resistant via the MeltPro assay were scored as LFX-susceptible based on pDST results. Ultimately, highly discordant LFX-resistance test results were associated with specific gyrA mutations in isolates with MICs approaching the critical LFX concentration.

Copyright © 2020. Published by Elsevier Inc.