β-Lactamase type, multidrug resistance and the association with virulence in third-generation cephalosporin-resistant Klebsiella pneumoniae.

Introduction. Third-generation cephalosporin-resistant Klebsiella pneumoniae (3GC-R-KP) is a significant global health concern. The widespread production of β-lactamases and virulence factors contributes to multidrug resistance and complicates treatment.Hypothesis/Gap Statement. The potential co-evolution of resistance and virulence in 3GC-R-KP remains unclear, raising the risk of emerging 'highly resistant-hypervirulent' clones.Aim. To analyse the resistance spectrum, virulence characteristics and biofilm formation ability of 3GC-R-KP and to clarify its enzyme production types and carriage of virulence factors.Methodology. The antimicrobial susceptibility of each strain, the hypermucoviscous (HM) phenotype (determined by the string test) and the biofilm-forming capacity (assessed using the crystal violet staining method) were examined. Three β-lactamase phenotypes were detected using the double disc synergy test, the disc approximation test and the modified carbapenem inactivation method, respectively. Simultaneously, multiplex PCR technology was employed to screen for drug resistance genes and virulence genes, and statistical analysis was performed on the detection results.Results. Most isolates were multidrug-resistant strains with biofilm-forming ability, and the main resistance phenotypes were extended-spectrum β-lactamase (ESBL) and carbapenemase production. Genotypically, bla SHV (95.8%; note: this represents only the carriage rate of the gene, and the wild-type does not possess ESBL activity) and bla KPC (76%) were the most common. The virulence genes entB (99%) and mrkD (96.9%) were detected at extremely high rates, indicating that drug-resistant strains generally possess high virulence potential, and there is a coexistence of resistance and virulence genes.Conclusion. 3GC-R-KP exhibits a high rate of multidrug resistance and widespread carriage of hypervirulence genes. Traditional hypervirulent K. pneumoniae (hvKP) is evolving into 'dual-risk' strains that possess both hypervirulence and multidrug resistance by acquiring resistance genes, thereby posing an increased clinical threat. The HM phenotype alone is insufficient to define hvKP, and accurate typing requires the detection of virulence genes. The co-occurrence of resistance genes and virulence factors suggests possible coevolution between them.