Genome sequence of Vibrio anguillarum isolates carrying a novel class A β-lactamase VAN-1: do migratory fish transport novel resistance factors?

Objectives: The aim of the study was to understand the genetic basis of resistance of five β-lactam resistant Vibrio anguillarum isolates obtained from the gut content of Atlantic mackerel (Scomber scomberus), using whole genome sequencing and to characterize a novel β-lactamase (VAN-1) from these isolates.

Method: Antibiotic sensitivity pattern was determined using Sensititre™ plates and whole genome sequencing was carried out using Illumina MiSeq-based sequencing. The bla gene was synthesized and expressed in Escherichia coli Top10 cells.

Results: Five isolates obtained (out of 73) from the gut content of Atlantic mackerel were identified as Vibrio anguillarum. Whole genome assemblies ranged from 3.894 to 3.906 million bases in length with an average of 50 contigs. A novel β-lactamase bla, sharing 77.7% nucleotide identity with a known mobile β-lactamase from Vibrio species was detected. The bla gene in these isolates is flanked by a truncated IS5 family transposase on one end and a hypothetical protein and outer membrane protein followed by another IS5 family transposase on the other end, suggesting its potential for mobility. The bla gene was absent in V. anguillarum type strain (ATCC 14181) and V. anguillarum isolates from bivalves and sea water in Norway. VAN-1 conferred ampicillin resistance when expressed in E. coli, thus confirming the functionality of this gene.

Conclusions: Our study highlights the importance of the marine environment as a reservoir of new antibiotic resistance genes. Our results suggest that migratory fish may transport novel antibiotic resistance determinants over long distances.