First Report of a Carbapenem-Resistant Comamonas resistens Strain Co-Carrying blaIMP-8 and Two Putative Rare β-Lactamase Genes, blaCAE-1 and blaPAU-1, in China
Background Carbapenems are among the last-line antibiotics for treating severe Gram-negative infections. Comamonas spp. are increasingly recognized for their clinical pathogenicity; however, carbapenem-resistant isolates have rarely been documented. Methods Species identification was confirmed by MALDI-TOF MS and whole-genome sequencing. Antimicrobial susceptibility testing (AST) was determined via Vitek 2 Compact. Genomic features and genetic environments of resistance genes were analyzed using comparative genomics, with iTOL, Easyfig, and BRIG for visualization. Results In this study, we identified and characterized a carbapenem-resistant C. resistens strain, CRSM1, from a pooled clinical fecal sample in China. AST revealed a multidrug-resistant phenotype, with the strain resistant to most β-lactams (including imipenem and meropenem), aminoglycosides, and fluoroquinolones, while remaining susceptible only to tigecycline and minocycline. Whole genome analysis identified a novel 42.8 kb plasmid, pCRSM1, which carries 12 resistance genes, including carbapenemase blaIMP-8 and two putative rare β-lactamases, blaCAE-1 and blaPAU-1. Genetic environment analysis showed that blaIMP-8 lies within a class 1 integron carrying a gene cassette array consisting of aac(6′)-Ib, a hypothetical protein gene, and blaIMP-8. blaCAE-1 is associated with a conserved IScaq2-ampR-blaCAE-1-ΔIScaq2-IScaq1 structure, and blaPAU-1 forms a conserved backbone with ampR adjacent to an IS6 element. Despite the absence of conjugative genes, these mobilization elements suggest the potential for horizontal transfer. Conclusion To our knowledge, this is the first report of a carbapenem-resistant C. resistens strain co-harboring blaIMP-8, blaCAE-1, and blaPAU-1 in China, underscoring the need to monitor Comamonas spp. as reservoirs of clinically significant resistance genes.