SME-4-producing Serratia marcescens from Argentina belonging to clade 2 of the S. marcescens phylogeny.

BACKGROUND

SME carbapenemases are increasingly reported, especially from North and South America. Here, we describe an SME-4-producing Serratia marcescens (SME-Sm) clinical isolate from Argentina and compare its genome with other SME-Sm and Sm isolates recovered from public databases.

METHODS

Sm isolates were characterized by WGS using Illumina technology, susceptibility testing and MIC determination. Carbapenemase activity was revealed by biochemical tests based on imipenem hydrolysis. A whole-genome phylogeny was estimated for all the Sm isolates retrieved from public databases with kSNP3 and a whole-genome phylogenetic analysis based on non-recombinant core SNPs was inferred for Sm complete genomes and for those encoding any blaSME variants.

RESULTS

Sm163 was resistant to amoxicillin, temocillin, aztreonam and carbapenems, remaining susceptible to extended-spectrum cephalosporins. WGS analysis of Sm163 revealed a genome of 5139329 bp and a chromosomally encoded blaSME-4 carbapenemase gene located on a genomic island closely related to SmarGI1-1 of Sm N11-02820. Comparison of the Sm genomes revealed that the 14 SME-Sm isolates possess this genomic island inserted at the same loci, that 13/14 belong to clade 1 and that 11/14 form a well-defined subcluster of cluster I of Sm clade 1, while Sm163 belongs to clade 2, suggesting that an SME-encoding genomic island may have been transferred between isolates from different clades.

CONCLUSIONS

To the best of our knowledge this is the first report of an SME-4-encoding Sm from Argentina. The blaSME-4 gene is located on a SmarGI1-1-like genomic island. The genome of Sm163 belongs to clade 2, unlike all the other SME-Sm isolates, which belong to clade 1.