Phenotypic and genomic characterization of tigecycline-insensitive Klebsiella pneumoniae strains and validation of highly virulent MDR strains.

UNLABELLED: Tigecycline is often used as a last-resort antibiotic to combat multidrug-resistant Klebsiella pneumoniae (MDR-KP). However, reports of tigecycline resistance are increasing. Thirty-two tigecycline-insensitive K. pneumoniae (TIKP) strains were detected among 152 MDR-KP isolates obtained from a tertiary hospital in China (21%). Whole-genome sequencing (Illumina NovaSeq 6000) revealed that these 32 TIKP isolates carried 119-127 virulence genes, 38-63 resistance genes, and 21 distinct sequence types (STs), including a novel ST (8597), together with 102,632 single-nucleotide polymorphisms. The predominant plasmid types included IncFIB(K) (10/32), IncFII(K) (11/32), IncR (11/32), RepB (13/32), and IncHI1B(pNDM-MAR) (12/32). The biofilm formation and serum resistance of the four strains were tested with a Galleria mellonella infection assay and whole-genome sequencing (PacBio platform). Among these strains, strain 10 showed strong biofilm formation and the strongest serum resistance. Compared with the other strains, it carried the most plasmids, and its chromosomes and plasmids harbored numerous resistance genes and contained more tigecycline resistance genes. These findings demonstrate the complex genetic features and potential transmission mechanisms of TIKP isolates.

IMPORTANCE

Our study revealed a high proportion (21%) of tigecycline-insensitive K. pneumoniae (TIKP) strains. We further characterized these TIKP isolates phenotypically and genomically, confirming the presence of highly virulent multidrug-resistant (MDR) strains. We discovered a novel allele (phoE 813) and a novel ST (8597). Our findings are significant because phenotypic analysis of TIKP allows clear determination of the level of tigecycline resistance (TRKP), which aids in optimizing antibiotic therapy and supports more rational clinical drug use. In addition, the plasmid-mediated resistance genes (e.g., the concurrent presence of both mcr-8 and tmexCD-toprJ in strain 10 in this study) may spread through the environmental-animal-human transmission chain. These results provide valuable insights for developing strategies to monitor and control the spread of TIKP.