Microbiome disruption and recovery in the fish Gambusia affinis following exposure to broad-spectrum antibiotic Jeanette M Carlson,1 Annie B Leonard,1 Embriette R Hyde,2,3 Joseph F Petrosino,2,3 Todd P Primm1 1Department of Biological Sciences, Sam Houston State University, Huntsville, 2Alkek Center for Metagenomics and Microbiome Research, 3Integrative Molecular and Biomedical Sciences Training Program, Department of Molecular Virology & Microbiology, Baylor College of Medicine, Houston, TX, USA Abstract: Antibiotics are a relatively common disturbance to the normal microbiota of humans and agricultural animals, sometimes resulting in severe side effects such as antibiotic-associated enterocolitis. Gambusia affinis was used as a vertebrate model for effects of a broad-spectrum antibiotic, rifampicin, on the skin and gut mucosal microbiomes. The fish were exposed to the antibiotic in the water column for 1 week, and then monitored during recovery. As observed via culture, viable counts from the skin microbiome dropped strongly yet returned to pretreatment levels by 1.6 days and became >70% resistant. The gut microbiome counts dropped and took longer to recover (2.6 days), and became >90% drug resistant. The resistance persisted at ~20% of skin counts in the absence of antibiotic selection for 2 weeks. A community biochemical analysis measuring the presence/absence of 31 activities observed a 39% change in results after 3 days of antibiotic treatment. The antibiotic lowered the skin and gut microbiome community diversity and altered taxonomic composition, observed by 16S rRNA profiling. A 1-week recovery period did not return diversity or composition to pretreatment levels. The genus Myroides dominated both the microbiomes during the treatment, but was not stable and declined in abundance over time during recovery. Rifampicin selected for members of the family Comamonadaceae in the skin but not the gut microbiome. Consistent with other studies, this tractable animal model shows lasting effects on mucosal microbiomes following antibiotic exposure, including persistence of drug-resistant organisms in the community. Keywords: microbiome, antibiotic, antibiotic resistance, Gambusia affinis, community disruption