ABSTRACT
Objective@#To establish a Galleria mellonella model of liver abscess-related Klebsiella pneumoniae (K.pneumoniae) infection and to evaluate its feasibility for virulence detection.@*Methods@#Twelve liver abscess-related K. pneumoniae strains were collected in Wuxi No.2 People′s Hospital from January 2016 to December 2017. Twenty K. pneumoniae strains isolated from sputum and urine samples were used as classic strains. All isolates were analyzed by String test. Common capsular serotypes (K1, K2, K5, K16, K20, K54 and K57) of highly virulent K. pneumoniae strains were detected by PCR. Virulence test was performed to measure 80% lethal doses (LD80) of different serotypes in the same time period and the lethal time for 80% of larvae (LT80) at the same concentration.@*Results@#The 12 strains of liver abscess-related K. pneumoniae belonged to five serotypes, which were K1 (41.7%, 5/12), K2 (8.3%, 1/12), K5 (8.3%, 1/12), K20 (8.3%, 1/12) and K57 (33.4%, 4/12). High-virulence serotypes were not detected in the classic group. The positive rates of String test in the liver abscess group and the classic group were 75% and 10% (2/20), respectively. Results of the virulence test showed that when the concentration ranged from 1×105 CFU/ml to 1×108 CFU/ml, the lethal effects of different strains on Galleria mellonella larvae were in a concentration dependent manner. Twelve hours after infection, the numbers of dead larvae in K1 and K57 serotype groups were significantly higher than those in K2, K5, K20 and classic groups. The LD80 values of the liver abscess group at 96 hours after infection were as follows: 1×106 CFU/ml (K1, K57) and 1×107 CFU/ml (K2, K5, K20).@*Conclusion@#The liver abscess-related K. pneumoniae isolates are all highly virulent strains. The virulence of K. pneumoniae can be detected at 12 hours after infection of Galleria mellonella.
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.