Whole-genome sequencing of NDM-1-producing ST85 Acinetobacter baumannii isolates from Tunisia.

BACKGROUND

New Delhi metallo-β-lactamase (NDM)-producing Acinetobacter baumannii have been described in several countries worldwide, and studies have suggested that Acinetobacter spp. could play the role of intermediate progenitor of the bla gene between environmental progenitor and Enterobacteriaceae.

MATERIALS AND METHODS

In total, 246 carbapenem-resistant A. baumannii isolates from a teaching hospital in Sousse, Tunisia were investigated between 1 June 2013 and 31 December 2015 to detect metallo-ß-lactamase (MBL) production. Polymerase chain reaction (PCR), antibiotic susceptibility testing, and genetic and whole-genome sequencing tools were used to study the underlying carbapenem resistance mechanisms.

RESULTS

PCR screening of the 246 carbapenem-resistant A. baumannii isolates revealed that 242 of 246 isolates harboured carbapenemase genes (seven of 246 positive for bla, four of 246 positive for bla and bla, 231 positive for bla). Conjugation and electroporation experiments suggested that the bla gene is likely to be chromosomally located. All the NDM-1-producing A. baumannii isolates were clonally related, and belonged to ST85 according to the Pasteur Institute's multi-locus sequence typing scheme. Analysis of the immediate genetic environment of the bla gene revealed that the gene was located within a truncated isoform of Tn125 transposon (ΔTn125). The bla gene was located within transposon Tn2008.

CONCLUSION

This study showed the dissemination of a single clone of NDM-1-producing A. baumannii in a Tunisian hospital. Countries in north Africa may constitute a significant reservoir for NDM-1-producing A. baumannii. The spread of the bla gene in A. baumannii was linked to clonal spread in this study.