Virulence and antimicrobial resistance profiling of Klebsiella pneumoniae isolated from foxes in northern China.

Klebsiella pneumoniae is a significant opportunistic pathogen in animal farming. To investigate the occurrence of K. pneumoniae and associated antimicrobial resistance risk in foxes, this study collected 350 fecal samples from foxes across five northern Chinese provinces. A total of 163 K. pneumoniae isolates were recovered (isolation rate: 46.57%), and all isolates were classified as multidrug-resistant (MDR). All isolates were resistant to azithromycin and sulfisoxazole, with high resistance to enrofloxacin (98.16%), ciprofloxacin (87.12%), and tetracycline (70.55%). Resistance to tigecycline and polymyxin B was lower. Notably, all isolates were susceptible to meropenem. Antimicrobial resistance gene (ARG) analysis revealed high carriage rates of tet(E), aac(3)-IIa, and qnrS, alongside the colistin resistance genes mcr-1 and mcr-8. Whole-genome sequencing of 66 isolates revealed substantial genetic diversity: 45 sequence types (STs) were identified among 64 typeable isolates, with ST35 and ST603 being the most common (5/64, 7.81% each), and lineages previously reported in human clinical settings (e.g., ST307 and ST15) were also detected; however, no direct cross-host transmission was evaluated in this study. Capsular types KL22 (10/64, 15.63%) was the most common. Metagenomic analysis further showed that the fox gut microbiome harbored diverse ARGs, with 29 ARGs detected in both K. pneumoniae isolates and fox gut resistome datasets (descriptive overlap). Among these, 20 genes (e.g., blaCTX-M-55 and aac(3)-IIa) were located on predicted plasmids or transposons, suggesting potential mobility rather than confirmed transfer. Conjugation assays provided limited proof-of-concept evidence for plasmid-mediated transfer of tet(A) and tet(E). Collectively, these findings suggest that farmed foxes may serve as potential reservoirs of MDR K. pneumoniae and transferable resistance determinants, supporting the need for continued surveillance and prudent antibiotic use within a One Health framework.