The Atlanta urban watershed harbors antibiotic-resistant halotolerant bacteria

Rapid urbanization of the Chattahoochee River has decreased the water quality with higher levels of anthropogenic bacteria from nonpoint source pollution. Introduced bacteria are variable across urban watersheds but only monitored by the abundance of fecal indicator bacteria. Staphylococcus aureus is a halotolerant, opportunistic pathogen associated with aquatic pollution, but impact on the microbial ecology is not well understood in freshwater systems. Describing the halotolerant subset of the aquatic microbiome, can expand upon the health risk of bacterial pollution.

Surface water samples along the Chattahoochee River were collected and halotolerant bacteria were cultured using selective agar, typical for growing Staphylococcus species. Bacteria colonies were isolated then characterized by morphology, biochemical tests, and antibiotic resistance screening. Antibiotic resistance profiles showed isolates with a high percentage of resistance to penicillin (86.2%) and novobiocin (17.2%). Biofilm formation was common with 41.4% of isolates formed moderate-to-strong biofilms. 16S rRNA gene sequencing identified isolates to not be Staphylococcus spp. but within two predominant groups, Bacillus spp. and Priestia spp.

The Priestia genus is poorly known in freshwater systems; though the combination of antibiotic resistance, biofilm formation, and spore-forming traits indicate that it has key survival characteristics. Halotolerant bacteria harbor opportunistic human pathogens and a public health risk because the bacteria have a high prevalence of antibiotic resistance and biofilm capability, which contribute to environmental persistence and reservoirs for antibiotic resistance genes. This environmental resistome is a notable and developing characteristic of the urban aquatic microbiome.