Putative transmission of extended-spectrum β-lactamase-producing Escherichia coli among men who have sex with men in Amsterdam, the Netherlands.

Objectives: A previous study showed higher prevalence of Escherichia coli (E. coli) expressing extended-spectrum β-lactamases (ESBL-Ec) among men who have sex with men (MSM) in Amsterdam, the Netherlands, compared with the general Dutch population. This study genetically characterised the ESBL-Ec isolates and investigated whether the increased prevalence could be explained by transmission between participants.

Methods: Whole-genome sequences were obtained from 93 unique ESBL-Ec isolates that were cultured from rectal swabs of 79 participants. Isolates were typed according to the Achtman MLST scheme and ESBL and virulence genes were identified. Pairwise SNP distances were determined between isolates. Isolate pairs with ≤ 25 SNPs were considered part of a putative transmission event, and events between multiple participants formed putative transmission clusters. To investigate whether putatively transmitted isolates belonged to globally expanded lineages, the level of hierarchical clustering with international isolates was assessed using core genome MLST (cgMLST) implemented on the Enterobase platform.

Results: The most frequently detected E. coli types were ST131:bla (16 of 117, 13.5%), ST131:bla, ST3075:bla and ST14:bla (all six of 117, 6.5%). Fourteen putative transmission events were identified, forming four putative transmission clusters. The largest putative transmission cluster contained ST131 isolates, which clustered with multiple international isolates in SNP and cgMLST analysis. One other transmission cluster (ST14:bla) and two transmission events (ST14:bla and ST394:bla) contained very rarely reported strains.

Conclusions: The identification of unique ESBL-Ec strains involved in putative transmission and carried by multiple participants demonstrated a high probability of ESBL-Ec transmission between MSM in Amsterdam; therefore, ESBL-Ec infection should be considered in cases of sexually active MSM having associated symptoms.