Emergence of IncHI2 plasmids carrying mcr-9 in ESBL-producing, multidrug resistant Salmonella Typhimurium and monophasic variant ST34 from food-producing animals in Italy

Colistin is a last resort antibiotic of the polymyxin family, increasingly used for treating human invasive infections by multidrug-resistant or extensively drug-resistant Enterobacteriaceae (Poirel et al., 2017). To date, ten different mcr genes have been reported worldwide in Enterobacteriaceae (Wang et al., 2020), with six mcr homologues (mcr-1 to -5 and mcr-9) identified so far in Salmonella enterica (Lima et al., 2019). In this study, we have sequenced three mcr-9 positives and one mcr-1 monophasic S. Typhimurium to characterise the genetic environment of mcr-9 gene and fully reconstruct the mcr-9 harbouring-plasmids by using a combined Illumina-Oxford Nanopore WGS approach.