Hospital outbreak of carbapenem-resistant Enterobacterales associated with a plasmid carried mostly by ST399.

A hospital outbreak of carbapenem-resistant Enterobacterales was detected by routine surveillance. Whole genome sequencing and subsequent analysis revealed a conserved promiscuous carrying plasmid as the defining factor within this outbreak. Four different species of Enterobacterales were involved in the outbreak. ST399 accounted for 35 of all the 55 isolates. Comparative genomics analysis using publicly available ST399 genomes showed that the outbreak ST399 isolates formed a unique clade. We developed a mathematical model of pOXA-48-like plasmid transmission between host lineages and used it to estimate its conjugation rate, giving a lower bound of 0.23 conjugation events per lineage per year. Our analysis suggests that co-evolution between the pOXA-48-like plasmid and ST399 could have played a role in the outbreak. This is the first study to report carbapenem-resistant ST399 carrying blaOXA-48 as the main cause of a plasmid-borne outbreak within a hospital setting. Our findings suggest complementary roles for both plasmid conjugation and clonal expansion in the emergence of this outbreak.