Antibiotic resistance and molecular characterization of carbapenem-resistant Klebsiella pneumoniae rectal colonization strains in a teaching hospital in China

Abstract Background Carbapenem-resistant Klebsiella pneumoniae (CRKP)’s intestinal colonization could serve as a source and reservoir of infection. Screening for and characterizing CRKP rectal colonization strains among hospitalized patients is a key measure to mitigate transmission and prevent outbreaks. Methods Rectal swabs were prospectively collected on admission day (T1) and after 2 week of hospitalization (T2) from the inpatients for detection of CRKP colonization between January 2025 and December 2025. Antimicrobial and biocide susceptibility testing were performed using broth dilution method to investigate the antibacterial activity of the 16 antibiotics and 5 biocides against, with resistance-related genes (carbapenemase, mobilized colistin resistance (mcr), and efflux pump genes) detected by PCR. The hypervirulent phenotype was analyzed by string test, PCR, and mouse experiments. Results A total of 299 CRKP isolates were collected from 7510 rectal swab samples, whcih were obtained from 70 patients at T1 and 229 patients at T2. The isolates were 100% resistant to the commonly used β-lactams, with low susceptibility to fluoroquinolones. The MIC values of biocides were generally higher than those of the standard strains. Among the tested genes, bla KPC (94.65%) and qacE∆1 (24.08%) were more prevalent. Two isolates carried the specific genes indicative of hypervirulence and caused significantly higher mortality rate, which were ultimately established as hypervirulent K. pneumoniae strains. Conclusion The high CRKP colonization rate highlighted the crucial value of active surveillance. The coexistence of antibiotic, efflux pump genes and hypervirulence underscores the need for vigilant surveillance and stringent infection control strategies.