Development of a quadruple qRT-PCR assay for simultaneous identification of hypervirulent and carbapenem-resistant Klebsiella pneumoniae

The increasing prevalence of hypervirulent (hv) and carbapenem-resistant (CR) Klebsiella pneumoniae (Kp) highlights the importance of timely and accurate differential diagnosis for epidemiological investigation and clinical management. A multiplex quantitative real-time PCR (qRT-PCR) assay for the simultaneous identification of hvKp and CR-Kp was developed and validated with excellent performance in sensitivity and specificity. Generally, the gltA gene for Kp, the iucA, rmpA and rmpA2 genes for hvKp, and the Klebsiella pneumoniae carbapenemases (KPC) gene for CR-Kp were included in the qRT-PCR assay. The detection limits for classic Kp (cKp), CR-cKp, hvKp, and CR-hvKp strains could all reach 50 genome equivalent copies and 20 CFUs per reaction with high accuracy (R-2 > 0.99) and reliability (CV values < 3%). Detection results from 84 Kp positive clinical samples showed 31 hvKp with 8 CR-hvKp and 53 cKp with 1 CR-cKp strains. The presence of virulence-associated factors for the identified hvKp and KPC genes for CR-Kp was confirmed by previously developed conventional PCR and antimicrobial susceptibility tests, respectively. Furthermore, the qRT-PCR identified hvKp strains showed mortality rates of >= 40% in the outbred murine infection model, while no death for the identified cKp strains. These results indicated that our multiplex qRT-PCR assay could accurately identify hvKp and CR-Kp strains, which will be of great use for the rapid and accurate diagnosis in a clinical setting and the surveillance of the circulating Kp.