Genetic Characterization of Antimicrobial-Resistant Isolated from a Mixed-Use Watershed in Northeast Georgia, USA.

In order to determine the role of surface water in the development and spread of antibiotic-resistant (AR) bacteria, water samples were collected quarterly from 2015 to 2016 from a mixed-use watershed in Georgia. In our previous study, 496 were isolated from surface water, out of which, 34 isolates were resistant to antimicrobials. For the current study, these 34 AR were characterized using pulsed-field gel electrophoresis, AR gene detection, plasmid replicon typing, class I integron detection, and multi-locus sequence typing. Genes were identified as conferring resistance to azithromycin ((A)); β-lactams (, , ); chloramphenicol (); streptomycin (, ); sulfisoxazole (, ); tetracycline (, , ); and trimethoprim/sulfamethoxazole (, ). Five ciprofloxacin- and/or nalidixic-resistant isolates contained point mutations in and/or . Most of the isolates (n = 28) carried plasmids and three were positive for class I integrons. Twenty-nine sequence types (ST) were detected, including three epidemic urinary-tract-infection-associated ST131 isolates. One of the ST131 isolates exhibited an extended-spectrum β-lactamase (ESBL) phenotype and carried and . To our knowledge, this is the first study on the emergence of an ESBL-producing ST131 from environmental water in the USA, which poses a potential risk to human health through the recreational, agricultural, or municipal use of this natural resource. This study identified with AR mechanisms to commonly used antimicrobials and carrying mobile genetic elements, which could transfer AR genes to other bacteria in the aquatic environment.