Versatile lifestyles of <i>Edwardsiella</i>: Free-living, pathogen, and core bacterium of the aquatic resistome

Abstract

<i>Edwardsiella</i> species in aquatic environments exist either as individual planktonic cells or in communal biofilms. These organisms encounter multiple stresses, include changes in salinity, pH, temperature, and nutrients. Pathogenic species such as <i>E. piscicida</i>, can multiply within the fish hosts. Additionally, <i>Edwardsiella</i> species (<i>E. tarda</i>), can carry antibiotic resistance genes (ARGs) on chromosomes and/or plasmids, that can be transmitted to the microbiome via horizontal gene transfer. <i>E. tarda</i> serves as a core in the aquatic resistome. <i>Edwardsiela</i> uses molecular switches (RpoS and EsrB) to control gene expression for survival in different environments. We speculate that free-living <i>Edwardsiella</i> can transition to host-living and vice versa, using similar molecular switches. Understanding such transitions can help us understand how other similar aquatic bacteria switch from free-living to become pathogens. This knowledge can be used to devise ways to slow down the spread of ARGs and prevent disease outbreaks in aquaculture and clinical settings.