Colistin Resistance Mediated by in ESBL-Producing, Multidrug Resistant Infantis in Broiler Chicken Industry, Italy (2016-2017).

Colistin-resistance mediated by mobilisable and plasmid-borne genes has emerged worldwide, threatening the efficacy of colistin, a last resort antibiotic increasingly used for treating human invasive infections by multidrug-resistant or extensively drug-resistant . In this study, we report the first evidence of -1-mediated colistin resistance in four multidrug resistant (MDR) out of 324 infantis from the Italian antimicrobial resistance (AMR) monitoring (2001-2017) in broilers and broiler meat. Two were also Extended Spectrum Beta-Lactamases (ESBL)-producing isolates. Characterization by whole genome sequencing (WGS), located -1.1 on an incX4 plasmid. Phylogenetic analysis of these isolates with selected Italian . Infantis previously isolated from animals, meat and human clinical cases with unknown epidemiological relationship, demonstrated that ESBL-producing, -1-positive isolates belonged to the emerging pESI-like-positive-ESBL-producing clone described in Italy in 2015.