Genome-facilitated discovery of RND efflux pump-mediated resistance to cephalosporins in Vibrio spp. isolated from the mummichog fish gut

Abstract

Objectives: This study examined the role of resistance-nodulation-cell division (RND) efflux pumps in resistance to first-generation and third-generation cephalosporins, and the potential contribution to increased virulence in two Vibrio isolates from the gut microbiota of a forage-feeder fish. Methods: Phenotypic MIC testing was performed in the presence and absence of an RND efflux pump inhibitor, phenylalanine-arginine-beta-napthylamide (PAβN). Genomes of the two Vibrio spp. were compared to characterise RND efflux pump gene homologs. Results: The study identified 13 and 12 RND operons, respectively, in Vibrio spp. T21 and T9, with Vibrio sp. T21 containing an additional RND operon compared with other V. parahaemolyticus strains. Both the inner-membrane protein (IMP) and the membrane facilitator protein (MFP) sequences of this operon were homologous to VexD and VexC, respectively, which is an RND operon in Vibrio cholerae. More generally, the other RND proteins in these strains showed homology to RND efflux pumps characterised in Escherichia coli and Vibrio cholerae. Decreased resistance to cefoperazone and cephradine was observed in Vibrio sp. T21, and to cefoperazone and cefsulodin in Vibrio sp. T9 in the presence of PaβN. The RND pumps may also mediate transport of kanamycin. Conclusions: By analysing the genomes of two Vibrio spp. isolated from the mummichog fish gut, RND efflux pump-mediated resistance to first-generation and third-generation cephalosporins was discovered in these strains. This work highlights the need for further research into this unique Vibrio spp. operon and, more generally, RND efflux pumps in Vibrio spp., as Vibrio spp. often cause seafood-borne illness.