Rapid detection of rmpA2-carrying hypervirulent Klebsiella pneumoniae by MALDI-TOF MS

Abstract

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) Key words: Klebsiella pneumoniae; Bacterial proteins; Transcription factors; Spectrometry, mass, matrix-assisted laser desorption-ionization