Acquisition and loss of CTX-M plasmids in species associated with MSM transmission in the UK.

Shigellosis in men who have sex with men (MSM) is caused by multidrug resistant Shigellae, exhibiting resistance to antimicrobials including azithromycin, ciprofloxacin and more recently the third-generation cephalosporins. We sequenced four -positive MSM isolates (2018-20) using Oxford Nanopore Technologies; three (identified as two MSM clade 2, one MSM clade 5) and one 3a, to explore AMR context. All isolates harboured Tn7/Int2 chromosomal integrons, whereas 3a contained the Resistance Locus. All strains harboured IncFII pKSR100-like plasmids (67-83kbp); where present was located on these plasmids flanked by IS and IS, however was lost in 3a during storage between Illumina and Nanopore sequencing. IncFII AMR regions were mosaic and likely reorganised by IS; three of the four plasmids contained azithromycin-resistance genes ) and ) and one harboured the pKSR100 integron. Additionally, all isolates possessed a large IncB/O/K/Z plasmid, two of which carried and ). Monitoring the transmission of mobile genetic elements with co-located AMR determinants is necessary to inform empirical treatment guidance and clinical management of MSM-associated shigellosis.