Whole genome sequencing of carbapenem-resistant : evolutionary analysis for outbreak investigation.

Carbapenemase-resistant represents a major concern in hospital setting. The evolutionary history of carbapenem-resistant strains was analyzed by core genome multilocus sequence typing and Bayesian phylogenesis by whole genomes sequencing. A great increase carbapenem-resistant causing blood stream infection was observed in the years 2015-2016. At multilocus sequence typing (MLST), they were prevalently ST512 and ST101. ST512 were core genome (cg)MLST 53, while ST101 mainly cgMLST453. The minimum-spanning tree, based on cgMLST, showed strains clustering based on the different STs. By Bayesian phylogenetic analysis, maximum clade credibility tree showed that strains were introduced in the year 2005 with the most probable location in the ICU ward. Two outbreaks by ST101 and ST512 strains with Tower T8 as the probable location were evidenced. Molecular epidemiology is a powerful tool to track the way of transmission of resistant bacteria within the hospital setting.