Serratia marcescensharbouring SME-type class A carbapenemases in Canada and the presence ofblaSME on a novel genomic island, SmarGI1-1

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An increasing prevalence since 2010 of Serratia marcescens harbouring the Ambler class A carbapenemase SME prompted us to further characterize these isolates.


Isolates harbouring blaSME were identified by PCR and sequencing. Phenotypic analysis for carbapenemase activity was carried out by a modified Hodge test and a modified Carba NP test. Antimicrobial susceptibilities were determined by Etest and Vitek 2. Typing was by PFGE of macrorestriction digests. Whole-genome sequencing of three isolates was carried out to characterize the genomic region harbouring the blaSME-type genes.


All S. marcescens harbouring SME-type enzymes could be detected using a modified Carba NP test. Isolates harbouring blaSME were resistant to penicillins and carbapenems, but remained susceptible to third-generation cephalosporins, as well as fluoroquinolones and trimethoprim/sulfamethoxazole. Isolates exhibited diverse genetic backgrounds, though 57% of isolates were found in three clusters. Analysis of whole-genome sequence data from three isolates revealed that the blaSME gene occurred in a novel cryptic prophage genomic island, SmarGI1-1.


There has been an increasing occurrence of S. marcescens harbouring blaSME in Canada since 2010. The blaSME gene was found on a genomic island, SmarGI1-1, that can be excised and circularized, which probably contributes to its dissemination amongst S. marcescens.

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