Genomic Epidemiology of Pseudomonas aeruginosa Sequence Type 111.

Purpose: Pseudomonas aeruginosa ST111 is a global multidrug resistant (MDR) high-risk clone and comprehensive data about its molecular epidemiology is limited in Canada. Comprehensive data about the evolution of ST111 clades is limited. We characterized a Canadian collection of ST111 causing bloodstream infections and investigated the genomic relationship between Canadian and global ST111.

Material and methods: We used long and short read WGS to characterize Canadian ST111 (n = 10 from 2010-18). We performed phylogenetic analysis on a global collection of ST111 (n = 969) and investigated the evolutionary history of clades using BEAST.

Results: ST111 belonged to 3 clades (A, B, C) and two subclades (C1, C2). ST111-A was the ancestral clade while clades B, C1 and C2 emerged during the 1700s and 1800s. ST111-C2 dominated the global ST111 population. Serotype switching from O4 to O12 and the acquisition of Tn21, gyrA_T83I, parC_S87L, In59 with bla_VIM-2 and aacA29 over time, were important in the evolution of ST111-C2. The Calgary ST111 strains consisted of a diverse collection that belonged to ST111-A (O4), ST111-C1 (O4) and ST111-C2 (O12) with different transposon structures.

Conclusions: We provided details on the emergence and evolution of different ST111 clades over time and highlighted the roles of serotype switching and the acquisition of certain AMR determinants and transposon structures in the evolution of ST111-C2.