Neutrophil bactericidal activity assay for detecting the virulence of hypervirulent Klebsiella pneumoniae / 中华微生物学和免疫学杂志

ABSTRACT

Objective To evaluate the feasibility of using neutrophil bactericidal activity assay for analyzing the anti-bactericidal ability of hypervirulent Klebsiella pneumoniae ( hvKP) strains that harbored the virulence genes of rmpA and rmpA2 and were positive for string test .Methods A total of 150 non-duplicate blood-borne Klebsiella pneumoniae strains were collected from Zhejiang Province from January 2016 to July 2017.PCR was performed to detect carbapenem resistance genes (blaKPC, blaNDM, blaIMP-1, blaIMP-2), cap-sule genotypes (K1, K2, K5, K20, K54 and K57) and virulence genes (rmpA, rmpA2, iucA and iroN). Klebsiella pneumoniae strains that were positive for string test and harbored rmpA and rmpA2 genes were iden-tified as hvKP strains, while classic Klebsiella pneumoniae (cKP) strains were negative for string test, rmpA or rmpA2 gene.Neutrophil bactericidal activity assay was performed to analyze the virulence of Klebsiella pneumoniae strains and the survival rate was determined by using the following equation the number of colony-forming units ( CFUs) in experimental group divided by the number of CFUs in control group .Re-sults Of the 150 Klebsiella pneumoniae strains, 43.3％ (65/150) harbored the rmpA2 gene and among them, strains positive for genes of rmpA, iroN and blaKPC and K2 respectively accounted for 73.8％, 80.0％, 75.4％and 40.0％.Twenty-four (36.9％) rmpA2 gene-positive strains showed positive result of string test.The survival rates of hvKP and cKP groups were respectively 0.866±0.056 and 0.368±0.058 and the difference between them was statistically significant (P<0.001).Conclusion Most of the hvKP strains that carry rmpA and rmpA2 genes and are positive for string test in Zhejiang Province survive the neu-trophil treatment , which indicates that the neutrophil bactericidal activity assay is an effective and simple method for identifying the virulence of Klebsiella pneumoniae.