Abstract
Hypervirulent Klebsiella pneumoniae strains are usually susceptible to many antimicrobial agents including colistin. Here we report the isolation and characterization of several colistin-resistant hypervirulent K. pneumoniae clinical strains. K. pneumoniae strains recovered from blood samples were collected at a university hospital in China. MICs of colistin were determined using microdilution. Colistin-resistant strains were subjected to whole genome sequencing to reveal their clonal background, antimicrobial resistance determinants and virulence factors. Virulence assays were performed with strains carrying the mucoid phenotype regulator gene rmpA using wax moth larvae. The pmrB gene encoding a P344L substitution was cloned into a colistin-susceptible K. pneumoniae strain to examine whether the substitution confers colistin resistance. Five colistin-resistant hypervirulent K. pneumoniae were recovered from blood samples of patients in China, belonging to four sequence/capsular types (ST23:K1, ST412:K57, ST660:K16, and ST700:K1) and carried the virulence factor rmpA. Three strains had the known colistin-resistant D150G substitution in PhoQ including one ST700:K1 strain also carrying mcr-1. The remaining two isolates had a P344L substitution of PmrB but cloning of pmrB encoding the substitution into a colistin-susceptible isolate did not alter MICs of colistin, suggesting that such a substitution did not confer resistance to colistin. In conclusion, the convergence of colistin resistance and hypervirulence in K. pneumoniae of multiple clonal backgrounds has emerged and may warrant further surveillance.
Highlights
Klebsiella pneumoniae is one of the most common bacterial pathogens isolated from clinical infections
Overnight cultures of K. pneumoniae strains were washed with phosphate-buffered saline (PBS) and further adjusted with PBS to concentrations of 1 × CFU/ml, 1 × CFU/ml, 1 × CFU/ml, 1 × CFU/ml
Among 112 Klebsiella strains collected from blood during the study period, five K. pneumoniae strains (Table 1) were found to be colistin resistant (MIC, 4 to 16 μg/ml; Supplementary Table S1) and hypervirulent and were included in this study
Summary
Klebsiella pneumoniae is one of the most common bacterial pathogens isolated from clinical infections. Certain sequence and capsular types (e.g., ST23:K1) of the organism display the hypermucoviscous phenotype and carry a number of critical virulence factors such as regulators of mucoid phenotype (rmpA, rmpA2), aerobactin (iucABCD, iutA), colibactin (clbA-R), salmochelin (iroN, iroBCD), and yersiniabactin (irp, ybtAEPQTUX) (Brisse et al, 2009; Holt et al, 2015). These hypervirulent K. pneumoniae (hvKP) are a particular threat for human health as they are able to cause severe infections in apparently healthy persons with high mortality (Shon and Russo, 2012). We report the isolation and characterization of five colistin-resistant hvKP clinical strains from different clonal backgrounds
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