MALDI-TOF mass spectrometry and blakpc gene phylogenetic analysis of an outbreak of carbapenem-resistant K. pneumoniae strains.

Carbapenem-resistant Klebsiella pneumoniae isolates are an important cause of nosocomial infections. This study evaluated a rapid cost-saving method based on MALDI-TOF technology, was and compared it with phenotypic, genotypic and epidemiological data for characterization of KPC-Kp strains consecutively isolated during a supposed outbreak. Twenty-five consecutive KPC Klebsiella pneumoniae isolates were identified and clustered by the MALDI Biotyper (Bruker, Daltonics). To display and rank the variance within a data set, principal component analysis (PCA) was performed. ClinProTools models were generated to investigate the highest sum of recognition capability and cross-validation. A Class dendrogram of isolates was constructed using ClinproTool. MLST was performed sequencing gapA, infB, mdh, pgi, rpoB, phoE and tonB genes. blakpc and cps genes were typed. Phylogenetic analysis and genetic distance of the KPC gene were performed using the MEGA6 software. PCA analysis defined two clusters, I and II, which were identified in a dendrogram by both temporal split and different antimicrobial susceptibility profiles. These clusters were composed mostly of strains of the same sequence type (ST512), the most prevalent ST in Italy, and the same cps (type 2). In cluster II, blakpc genotype resulted more variable than in cluster I. Phylogenetic analysis confirmed the genetic diversity in both clusters supported by the epidemiological data. Our study confirms that MALDI-TOF can be a rapid and cost-saving method for epidemiological clustering of KPC K. pneumoniae isolates and its association with blakpc genotyping represents a reliable method to recognize possible clonal strains in nosocomial settings.