Klebsiella pneumoniae is an important emerging pathogen leading to serious clinical outcomes as the multidrug-resistant (MDR) isolates arise. While K. pneumoniae is a well-known pathogen in human clinical settings, its risks in nonhuman hosts and potential for cross-species transmission remain poorly understood. In this study, we performed whole-genome sequencing on 112 K. pneumoniae isolates from four host sources in Northeast China to elucidate their phylogenetic relationships and characterize their antimicrobial resistance (AMR) and virulence profiles. Our analysis identified 53 distinct sequence types (STs), 38 K-locus (KL) types, and nine O-loci. Notably, several strains with identical ST-KL combinations were shared across different hosts: ST76-KL5 was detected in both human and dairy cow sources; ST412-KL57 was found in human and chicken; ST111-KL63 was present in both pig and dairy cow sources, suggesting potential interspecies transmission. Antimicrobial susceptibility testing (AST) showed that nearly all human- and pig-derived isolates were resistant to   -lactams, quinolones, co-trimoxazole, tetracyclines, and at least one aminoglycoside. In contrast, isolates from chickens and dairy cows exhibited lower resistance rates to these antibiotics. Overall, 88 of the 112 isolates (78.6%) were classified as MDR phenotype. Virulence gene screening indicated that 34 isolates carried the iucABCD/iutA aerobactin synthesis cluster, a key marker for hypervirulence. These iuc-positive strains fell into two distinct phylogenetic lineages, including iuc1 and iuc3. It is necessary to conduct the regular monitoring of the antibiotic resistance and hypervirulence of clinical K. pneumoniae from animals to prevent and control the transmission of K. pneumoniae along the food chain.

Keywords: Klebsiella pneumoniae; antimicrobial resistance; genotyping; virulence; whole-genome sequencing.