Characterisation of bla OXA-538 , a new variant of bla OXA-48 , in Shewanella xiamenensis isolated from river water in Algeria

In this study, the presence of carbapenemase genes in Shewanella xiamenensis strains isolated from river water in Béjaïa, Algeria, was investigated.Four isolates of S. xiamenensis were isolated from water from Soummam River. The isolates were identified by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS) and sequencing of the 16S rRNA and gyrB genes. Isolates were subjected to antimicrobial susceptibility testing. Carbapenemase production was screened using phenotypic tests. PCR and sequencing were used to identify carbapenemase genes in the isolates. The genetic context of the blaOXA-48-like gene was investigated by sequencing the whole genome of strain AS58.All four S. xiamenensis strains harboured blaOXA-48-like genes. They exhibited different resistance patterns and had imipenem minimum inhibitory concentrations (MICs) of ≥0.5mg/L. Sequencing of blaOXA-48-like genes from the S. xiamenensis isolates showed that two strains harboured blaOXA-181, one strain harboured blaOXA-199 and one strain exhibited a new variant of the blaOXA-48-like gene, named blaOXA-538. This new variant shared 98% nucleotide identity with blaOXA-162, with three amino acid changes (G201A, A213G and I219F). Conjugation assays with Escherichia coli J53 recipient were performed but no transconjugants were obtained. Analysis of the genome of AS58 Touati strain confirmed the chromosomal location of the blaOXA-538 gene.This study showed that environmental water holds a diversity of S. xiamenensis strains harbouring blaOXA-48-like genes and may play an important role in the dissemination and spread of these genes from the environment to humans.