Cardiff University, Division of Infection and Immunity, Department of Medical Microbiology, University Hospital of Wales, Cardiff, UK.
Public Heath England, Bacterial Reference Department, London, UK.
J Antimicrob Chemother. 2021 Apr 13;76(5):1197-1204. doi: 10.1093/jac/dkaa535.
There is a lack of international unification for AST methodology for Legionella pneumophila. Current literature contains multiple possible methods and this study compares each of them to determine methodological concordance.
Antibiotic susceptibility of 50 L. pneumophila strains was determined using broth microdilution (BMD), serial antimicrobial dilution in traditional buffered charcoal yeast extract (BCYE) agar (as well as comparison with gradient strip overlay on BCYE) and in a novel charcoal-free agar (LASARUS) for rifampicin, azithromycin, levofloxacin and doxycycline.
The deviation of tested media relative to BMD highlighted the overall similarity of BMD and LASARUS across all antimicrobials tested (within one serial dilution). BCYE agar dilution showed an increased MIC of up to five serial dilutions relative to BMD, while MICs by gradient strip overlay on BCYE were elevated by two to three serial dilutions, with the exception of doxycycline, which was decreased by three serial dilutions relative to MIC values determined by BMD. The MIC range for azithromycin was wider than for other antimicrobials tested and found to be caused by the presence or absence of the lpeAB gene.
BMD-based antimicrobial susceptibility testing (AST) methodology should be the internationally agreed gold standard for Legionella spp. AST, as is common for other bacterial species. Traditional BCYE gave significantly elevated MIC results and its use should be discontinued for Legionella spp., while MIC determination using LASARUS solid medium gave results concordant (within one serial dilution) with BMD for all antimicrobials tested. To the best of our knowledge, this study is the first to identify the lpeAB gene in UK isolates.
嗜肺军团菌的 AST 方法在国际上缺乏统一标准。目前的文献中包含多种可能的方法，本研究比较了每种方法，以确定方法的一致性。
使用肉汤微量稀释法（BMD）、传统缓冲炭酵母提取物琼脂（BCYE）中的连续抗菌稀释法（以及与 BCYE 上的梯度条覆盖法的比较）以及新型无炭琼脂（LASARUS）来测定 50 株嗜肺军团菌菌株对利福平、阿奇霉素、左氧氟沙星和强力霉素的药敏性。
与 BMD 相比，测试介质的偏差突出了 BMD 和 LASARUS 在所有测试抗菌药物中的总体相似性（在一个连续稀释范围内）。BCYE 琼脂稀释法与 BMD 相比，MIC 增加了多达五个连续稀释度，而 BCYE 上的梯度条覆盖法的 MIC 则增加了两个到三个连续稀释度，除了强力霉素，其 MIC 值相对于 BMD 测定值降低了三个连续稀释度。阿奇霉素的 MIC 范围比其他测试的抗菌药物更宽，这是由于 lpeAB 基因的存在或缺失所致。
基于 BMD 的抗菌药物敏感性测试（AST）方法应该是国际上公认的嗜肺军团菌 AST 的金标准，就像其他细菌物种一样。传统的 BCYE 琼脂会产生显著升高的 MIC 结果，应停止用于嗜肺军团菌，而使用 LASARUS 固体培养基进行 MIC 测定与 BMD 对所有测试的抗菌药物的结果一致（在一个连续稀释范围内）。据我们所知，本研究首次在英国分离株中鉴定出 lpeAB 基因。
