Brenciani Andrea, Massacci Francesca Romana, Albini Elisa, Cucco Lucilla, Russo Elisa, Nigro Maria Elena, Coccitto Sonia Nina, Cinthi Marzia, Simoni Serena, Paniccià Marta, Morroni Gianluca, Mingoia Marina, Magistrali Chiara Francesca, Vignaroli Carla, Giovanetti Eleonora
Unit of Microbiology, Department of Biomedical Sciences and Public Health, Polytechnic University of Marche Medical School, Via Tronto 10/A, Ancona 60126, Italy.
Department of Research and Development, Istituto Zooprofilattico Sperimentale dell'Umbria e delle Marche 'Togo Rosati', Perugia, Italy.
J Antimicrob Chemother. 2025 Jun 25. doi: 10.1093/jac/dkaf202.
To clarify the genetic basis of high-level linezolid resistance in three Clostridioides difficile strains from calves.
A WGS approach was used to comprehensively characterize C. difficile A501, A505 and A516 strains exhibiting high linezolid MICs, and to clarify their phylogenetic relationships. Linezolid resistance gene transferability was assessed by filter mating experiments.
WGS analysis revealed the presence of cfr(B) in C. difficile A501 and A516, both exhibiting the ST11, and cfr(C) in C. difficile A505 belonging to a non-toxigenic ST15 clone. The cfr(B) gene was on a novel 25 791 bp integrative conjugative element (ICE), named ICECd-cfr(B), similar to an uncharacterized region of Clostridium sp. C1, but significantly different from the Tn6218 transposon typically associated with this gene. The cfr(C) gene was found on a novel 32 770 bp ICE, named ICECd-cfr(C), which was identical to an uncharacterized region of the C. difficile DSM 104450 chromosome. ICECd-cfr(C) exhibited high nucleotide identity, but low coverage, with a cfr(C)-carrying region previously detected in C. difficile 020482; whereas in C. difficile A505 this region was interrupted by a 16.6 kb DNA insertion. Conjugation assays failed to demonstrate the transferability of cfr(B) and cfr(C) genes.
To the best of our knowledge, this is the first report of C. difficile isolates from calves with high linezolid MICs due to novel cfr(B)- and cfr(C)-carrying ICEs. C. difficile animal isolates, belonging to ST11 and ST15 clones with zoonotic potential, could act as reservoirs for the spread of linezolid resistance genes to human intestinal pathogens, with serious consequences for public health.
阐明来自犊牛的三株艰难梭菌菌株对利奈唑胺高水平耐药的遗传基础。
采用全基因组测序（WGS）方法全面表征表现出高利奈唑胺最低抑菌浓度（MIC）的艰难梭菌A501、A505和A516菌株，并阐明它们的系统发育关系。通过滤膜接合实验评估利奈唑胺耐药基因的可转移性。
WGS分析显示，艰难梭菌A501和A516中存在cfr(B)，二者均属于ST11型，而属于非产毒ST15克隆的艰难梭菌A505中存在cfr(C)。cfr(B)基因位于一个新的25791 bp整合性接合元件（ICE）上，命名为ICECd-cfr(B)，类似于梭菌属C1菌株的一个未表征区域，但与通常与该基因相关的Tn6218转座子有显著差异。cfr(C)基因位于一个新的32770 bp ICE上，命名为ICECd-cfr(C)，它与艰难梭菌DSM 104450染色体的一个未表征区域相同。ICECd-cfr(C)与先前在艰难梭菌020482中检测到的携带cfr(C)的区域表现出高核苷酸同一性，但覆盖率低；而在艰难梭菌A505中，该区域被一个16.6 kb的DNA插入中断。接合试验未能证明cfr(B)和cfr(C)基因的可转移性。
据我们所知，这是首次报道来自犊牛的艰难梭菌分离株因携带新的cfr(B)和cfr(C)的ICE而对利奈唑胺有高MIC。属于具有人畜共患病潜力的ST11和ST15克隆的艰难梭菌动物分离株可能成为利奈唑胺耐药基因传播到人类肠道病原体的储存库，对公共卫生造成严重后果。
