Occurrence of Phenotypic Multidrug-Resistant E. coli in Kentucky (USA) Surface Waters and Exploration of Sentinel Antibiotics for One Health Surveillance

Background/Objectives: Antimicrobial resistance (AMR) is a global public health threat, and surface waters may serve as surveillance locations for multidrug-resistant (MDR) bacteria within communities. This study explored MDR E. coli in Kentucky (USA) surface waters, primarily evaluating non-susceptibility to tetracycline, for assessing MDR associations. Methods: Surface water samples were collected from 47 sites in East-Central Kentucky during 2022 and 2024. Isolates were obtained using selective differential media, with and without tetracycline (TE) supplementation, targeting E. coli and TE-resistant E. coli. Species identification and antimicrobial susceptibility testing against 21 antibiotics representing 13 categories was performed with recovered presumptive E. coli isolates. MDR was defined as non-susceptibility to at least one antibiotic in three or more antimicrobial categories. Results: Of 151 isolates, 130 (86%) were identified as E. coli. Overall, 25% and 13% of recovered E. coli isolates from media with and without TE had MDR phenotypes, respectively, which included one isolate with non-susceptibility to 10 of 12 designated antibiotic categories. MDR prevalence was higher among incidentally recovered Enterobacter spp. (100%) than E. coli. TE non-susceptibility occurred in 100% and 18% of E. coli isolates recovered from TE-treated and untreated media, respectively. Ampicillin non-susceptibility occurred in 28% and 16% of E. coli isolates from TE-treated and untreated media. Among this non-random set of recovered isolates, ampicillin and cefazolin non-susceptibility demonstrated potential for MDR E. coli prediction. TE-treated media did not significantly improve MDR E. coli recovery. Conclusions: MDR E. coli and one potentially extensively drug-resistant (XDR) E. coli isolate were recoverable from Kentucky surface waters. Ampicillin and cefazolin non-susceptibility demonstrated potential as sentinel markers for informing screening media development for AMR surveillance in Kentucky waters.