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Objective@#To evaluate the ability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) in identifying the rmpA2-carrying hypervirulentKlebsiella pneumoniae.@*Methods@#A total of 57nonduplicateKlebsiella pneumoniae isolates were collected from the Second Affiliated Hospital of Zhejiang University and Henan Provincial People′s Hospital. Virulence gene rmpA2 and capsule K serotype-specific genes were detected by PCR, multilocus sequence typing (MLST) was performed for molecular typing, and string test was conducted to identify the hypermucoviscous phenotype. The ClinProTools software was used for peak analysis. Four standard algorithms, including support vector machine (SVM), genetic algorithm (GA), supervised neural network (SNN), and quick classifier (QC), were tested for their power to differentiate between rmpA2-positive and rmpA2-negative strains.@*Results@#Among the 57 Klebsiella pneumoniae isolates, 28 isolates belonged to sequence type (ST) 11 and carried the virulence gene rmpA2, of which 5 isolates were positive for string test; while the other 29 isolates were not detected rmpA2, and MLST divided them into five STs including ST11 (n=23), ST15 (n=3), ST1 (n=1), ST76 (n=1), and ST473 (n=1). The results of four standard algorithms were similar, while the sensitivity and specificity of SVM was the highest at 93.23% and 100% respectively. Analysis results of ClinProTools software suggested that the specific peaks for differentiating the rmpA2-positive and rmpA2-negative strains were 7 168.9 and 7 280.76, however, the peak intensity of themwere variant.@*Conclusion@#The sensitivity and specificity ofMALDI-TOF MS for rapid identification of rmpA2-carrying hypervirulentKlebsiella pneumoniae werehigher than 90% and there was a difference on the peak intensity of two specific peaks, which needs further study.(Chin J Lab Med, 2018, 41: 571-675)
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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.