Emergence of a hypervirulent carbapenem-resistant Klebsiella pneumoniae isolate from clinical infections in China

- For the first time, one hypermucoviscous CRKP isolate was identified as hypervirulent strain using mouse lethality assay.
- The hypervirulent CRKP strain was isolated from a 1-day-old male infant with septicemia.
- Significantly increased resistance to serum killing and mice mortality were found in the hypervirulent CRKP strain.
- The emergence of hypervirulent CRKP might cause serious infections, suggesting an urgent need to enhance our awareness.

SummaryObjectivesHypervirulent Klebsiella pneumoniae (hvKP) infections occur worldwide, but carbapenem-resistant hvKP strain has rarely been observed.MethodsA retrospective study was conducted in 28 cases of carbapenem-resistant K. pneumoniae (CRKP) infections from 9 cities in China. Clinical data were collected from medical records. All the isolates were characterized by antimicrobial susceptibility testing, string test, multilocus sequence typing, and capsular genotyping. All the hypermucoviscous CRKP strains were analyzed by virulence gene profiles, serum killing assay, and mouse lethality assay.ResultsOf 28 CRKP isolates, five were positive for string test. Importantly, one of the hypermucoviscous strains isolated from blood sample was identified as hvKP. The hypervirulent CRKP strain showed highly resistant to carbapenems (MIC > 32 μg/mL), decreased expression of ompK35/36, and ESBLs production. Significantly increased resistance to serum killing and mice mortality were found in the hypervirulent CRKP strain compared to the other CRKPs. Capsular polysaccharide synthesis genotyping revealed that the hypervirulent strain belongs to K2 serotype, while others belong to K-nontypable serotype. The K2 hypervirulent CRKP strain carried rmpA, aerobactin, entB, and mrkD genes.ConclusionsThe newly emerged hypervirulent carbapenem-resistant K. pneumoniae might cause a serious threat to public health, suggesting an urgent need to enhance clinical awareness and epidemiologic surveillance.