Antibiotic Resistance in Seawater Bacterial Communities Along the Mississippi Gulf Coast

Antibiotic-resistant bacteria are a potential concern in coastal environments, particularly those used for human activity such as beaches. We used a combination of culture and culture-independent 16S rRNA gene approaches to characterize antibiotic-resistant bacterial communities in seawater at seven beaches along the Mississippi Gulf Coast, USA. Antibiotic-resistant bacteria were present at all beaches sampled, with those resistant to amoxicillin being most common followed by those resistant to erythromycin. The composition and diversity of mixed culture bacterial communities varied more based on the antibiotic used in the culture media than the beach sampled. Cultured bacterial communities differed significantly from those in uncultured seawater and were substantially less diverse, but community 16S rRNA gene sequencing revealed more sequence types than identified through isolation. A total of 59 bacterial isolates were obtained and identified, with the most common genera being Pseudomonas, Vibrio, and Aeromonas. Over 80% of isolates showed some level of multi-drug resistance. These results show that antibiotic resistance is common and widespread among bacterial populations in seawater along the Mississippi Gulf Coast and that a combination of culture and molecular approaches can reveal a greater diversity of antibiotic-resistant taxa than identified by either approach alone.