MDR Shigella sonnei in Spain: an ever-evolving emerging threat?

BACKGROUND: Seven CTX-M-27-producing Shigella sonnei strains were isolated at the University Hospital Virgen del Rocío (Seville, Spain) microbiology service from October to November 2021. OBJECTIVES: To offer extensive information on the microbiological and molecular epidemiology results of the seven S. sonnei isolates and compare them with other previously documented CTX-M-27-producing S. sonnei associated with MSM transmission. METHODS: S. sonnei isolated from stool samples of patients with acute diarrhoea were identified through biochemical and serological typing. Whole characterization of the seven isolates was performed by sequencing with MinION Mk1C followed by genomic and molecular analysis. RESULTS: All the isolates were resistant to penicillins, cephalosporins, fluoroquinolones, cotrimoxazole and azithromycin. Sequencing showed the presence of several resistance determinants, outstanding bla(CTX-M-27), azithromycin resistance genes [ermB and mph(A)], qnrB19 and mutations in the QRDRs. All isolates belonged to the same hierarchical clustering of cgMLST (HierCC) with five allele distance (HC5) scheme v1 from EnteroBase. However, they presented differences in plasmid composition, with all seven isolates harbouring IncFII, IncB/O/K/Z and ColE1-like while SH2, SH6 and SH7 had IncFIB only. Our isolates were closely related to others from Spain (HC5; 98748), Australia (HC5; 98748) and the UK (HC5; 98748), which were also associated with MSM transmission. Nevertheless, the structure of the non-chromosomal genetic elements and the genetic context of bla(CTX-M-27) presented a certain variability compared with isolates from other countries and among them. CONCLUSIONS: This study confirms the emergence of CTX-M-27-producing S. sonnei (ST152) associated with MSM transmission in Spain, adding it to the Europe outbreak list and reinforcing the necessity of active surveillance and control of this high-risk clone.