Department of Parasitology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
Department of Medical Laboratory Science, College of Medical Science and Technology, I-Shou University, Kaohsiung, Taiwan.
J Antimicrob Chemother. 2023 Jul 5;78(7):1622-1631. doi: 10.1093/jac/dkad137.
Cefepime and aztreonam are highly efficacious against H. influenzae, and resistant strains are rare. In this study, we isolated cefepime- and aztreonam-nonsusceptible H. influenzae strains and addressed the molecular basis of their resistance to cefepime and aztreonam.
Two hundred and 28 specimens containing H. influenzae were screened, of which 32 isolates were enrolled and applied to antimicrobial susceptibility testing and whole-genome sequencing. Genetic variations that were detected in all nonsusceptible isolates with statistical significance by Fisher's exact tests were identified as cefepime or aztreonam nonsusceptibility related. Functional complementation assays were conducted to assess the in vitro effects of proteins with sequence substitutions on drug susceptibility.
Three H. influenzae isolates were nonsusceptible to cefepime, one of which was also nonsusceptible to aztreonam. Genes encoding TEM, SHV and CTX-M extended-spectrum β-lactamases were not detected in the cefepime- and aztreonam-nonsusceptible isolates. Five genetic variations in four genes and 10 genetic variations in five genes were associated with cefepime and aztreonam nonsusceptibility, respectively. Phylogenetic analyses revealed that changes in FtsI were correlated strongly with the MIC of cefepime and moderately with aztreonam. FtsI Thr532Ser-Tyr557His cosubstitution linked to cefepime nonsusceptibility and Asn305Lys-Ser385Asn-Glu416Asp cosubstitution to aztreonam nonsusceptibility. Functional complementation assays revealed that these cosubstitutions increased MICs of cefepime and aztreonam in susceptible H. influenzae isolates, respectively.
Genetic variations relevant to resistant phenotypes of cefepime and aztreonam nonsusceptibility in H. influenzae were identified. Moreover, the effects of FtsI cosubstitutions on increasing MICs of cefepime and aztreonam in H. influenzae were demonstrated.
头孢吡肟和氨曲南对流感嗜血杆菌具有高度疗效，且耐药菌株罕见。在本研究中，我们分离出对头孢吡肟和氨曲南均不敏感的流感嗜血杆菌菌株，并探讨了其对头孢吡肟和氨曲南耐药的分子基础。
筛选了 228 份包含流感嗜血杆菌的标本，其中 32 份分离株被纳入并进行了药敏试验和全基因组测序。通过 Fisher 精确检验发现，所有耐药分离株中具有统计学意义的遗传变异被鉴定为与头孢吡肟或氨曲南耐药相关。进行功能互补实验以评估具有序列取代的蛋白质对药物敏感性的体外影响。
有 3 株流感嗜血杆菌对头孢吡肟不敏感，其中 1 株对氨曲南也不敏感。在头孢吡肟和氨曲南耐药分离株中未检测到编码 TEM、SHV 和 CTX-M 型超广谱β-内酰胺酶的基因。在 4 个基因中有 5 个基因变异和在 5 个基因中有 10 个基因变异与头孢吡肟和氨曲南耐药相关。系统发育分析显示，FtsI 的变化与头孢吡肟的 MIC 密切相关，与氨曲南的相关性则适中。与头孢吡肟耐药相关的 FtsI Thr532Ser-Tyr557His 共取代以及与氨曲南耐药相关的 Asn305Lys-Ser385Asn-Glu416Asp 共取代与头孢吡肟耐药相关。功能互补实验显示，这些共取代分别增加了敏感型流感嗜血杆菌分离株中头孢吡肟和氨曲南的 MIC。
确定了与流感嗜血杆菌对头孢吡肟和氨曲南耐药表型相关的遗传变异。此外，还证明了 FtsI 共取代对增加流感嗜血杆菌中头孢吡肟和氨曲南 MIC 的影响。
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