Characterization of resistance determinants in clinical and environmental isolates of multi-resistant bacteria

The main focus of this PhD thesis is the research of the mechanisms of resistance to beta-lactam antibiotics in health-care associated multi-resistant gram-negative bacteria (mainly Enterobacteriaceae). In particular, a novel class D beta-lactamase with carbapenemase activity, named OXA-372 was characterized from a multi-resistant Citrobacter freundii isolated from hospital-wastewater. Other interesting isolates included in this work are the first NMCA-producing Enterobacter ludwigii, the first IMI-2-producing E. ludwigii and a VIM-1-producing Aeromonas caviae. Moreover a cfr-positive linezolid resistant isolate of MRSA was characterized. Multiple techniques of molecular biology were applied during this thesis including PFGE, MLST, Real Time PCR and Whole-Genome Sequencing. Part of this work included also the italian epidemiology of carbapenemase and ESBL in a large collection of Escherichia coli and Klebsiella pneumoniae isolated from 14 different centers in 2013.