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.