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 treat this zoonotic disease because of the rapid deterioration 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 57 C. canimorsus , C. cynodegmi , C. canis , C. felis , C. stomatis , and C. catalasegens isolates were assayed by E-test. Resistance genes were detected by 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 significant clinical implications, especially in antimicrobial treatment.