Investigation of antimicrobial susceptibility and resistance gene prevalence in Capnocytophaga spp. isolated from dogs and cats and characterization of novel class A β-lactamase CST-1.

Purpose: Capnocytophaga spp., common inhabitants of the animal oral cavity, are zoonotic pathogens transmitted to humans through dog/cat bites and cat scratches. Appropriate antimicrobial therapy is essential for treatment this zoonotic disease because of the rapid deterioration of systemic symptoms at disease onset; however, antimicrobial resistance of animal bite-associated Capnocytophaga spp. has not been fully investigated. We sought to understand the antimicrobial susceptibility and prevalence of resistance genes among Capnocytophaga sp. isolates obtained from dogs and cats.

Method: Minimum inhibitory concentrations (MICs) of nine antibiotics for a total of 57 isolates belonging to 6 species (C. canimorsus, C. cynodegmi, C. canis, C. felis, C. stomatis, and C. catalasegens) were assayed using E-test. Resistance genes were detected using polymerase chain reaction, nucleotide sequencing, and whole-genome sequencing.

Results: The MICs of penicillin, ceftriaxone, cefepime, clindamycin, minocycline, nalidixic acid, and ciprofloxacin were high for some isolates. The MICs of imipenem and amoxicillin/clavulanic acid were low for all isolates. Known resistance genes bla_cfxA2, bla_OXA-347, emrF, and tetQ were detected using polymerase chain reaction. Mutation in the quinolone resistance-determining region of gyrA was also detected. Cst-1, a previously unreported gene, was identified using whole-genome analysis of two C. stomatis isolates. CST-1 was proposed as a class A, subclass A2, β-lactamase based on amino acid sequence and phylogenetic relationship. In recombination experiments, CST-1 inactivated penicillin and first- and second-generation cephems; however, sulbactam inhibited it.

Conclusion: Known and novel resistance genes are prevalent among Capnocytophaga spp. in animal oral cavities. The findings have clinical implications, especially in antimicrobial treatment.