Antibiotic resistance, pathogenicity and genomic characteristics of a novel sequence type 6839 Klebsiella pneumoniae strain isolated from cultured bullfrogs (Rana catesbeiana)

Introduction Klebsiella pneumoniae is the most frequently encountered multidrug-resistant bacterial pathogen in humans, but its pathogenic effects on aquatic animals are not well documented. K. pneumoniae has recently been identified as a significant cause of death and illness in American bullfrogs ( Rana catesbeiana ). In the present study, the dominant bacteria were isolated from a diseased bullfrog with neurological signs in Hanchuan, Hubei Province, China. Methods The ZYRC75 isolate was identified by Gram staining, morphological observations, biochemical assays and 16S rRNA sequencing. Antimicrobial susceptibility testing and artificial infection testing were conducted to determine its resistance phenotype and pathogenicity. The whole genome of the ZYRC75 strain was also sequenced. Results The isolate ZYRC75 was identified as K. pneumoniae and assigned to ST6839, a novel sequence type. It displayed multidrug resistance against penicillins (carbenicillin, piperacillin, ampicillin, penicillin), chloramphenicol, trimethoprim and tetracycline. Infection experiments confirmed the isolate exhibited significant pathogenicity in bullfrogs. ZYRC75 possessed a single circular chromosome of 5,454,922 bp, carrying 179 virulence‑related genes and 157 antimicrobial‑resistance genes. Discussion This investigation presents a detailed phenotypic and genomic profile of ZYRC75, revealing its antimicrobial resistance and virulence, and establishing a basis for future studies on the pathogenicity of K. pneumoniae .