Antibiotic resistant bacteria in an urban freshwater ecosystem in central Texas

Antibiotic resistance is a growing concern for the human population and is becoming prevalent in many environments. For example, increasing occurrences of antibiotic resistance genes (ARGs) in aquatic ecosystems elevates the risk of pathogenic microbes acquiring those resistance genes. There is an urgent need to more closely examine the relationship between antibiotic resistant bacteria (ARB) and antibiotic residues in urban freshwater environments. Thus, our main objective was to investigate the presence of antibiotic resistance in wastewater treatment plant (WWTP) influent and effluent leading into the Brazos River using several commonly used antibiotics: penicillin, ciprofloxacin, erythromycin, trimethoprim, tetracycline, sulfamethoxazole, and gentamicin. An additional aim was to explore possible mechanisms of resistance emergence to these antibiotics using techniques such as replica plating, the Luria-Delbrück Fluctuation Test, the Newcombe Test, and 16S rRNA sequencing. Four samples of influent and treated effluent wastewater were collected from the WWTP to enumerate resistant bacteria in the community and to investigate whether mutations causing resistance in ARB might be induced or spontaneous. We found that penicillin had the highest rate of resistance in all samples and that a similar trend of resistance appeared across all four samples. According to the Luria–Delbrück Fluctuation Test and the Newcombe Test, different antibiotics appear to be associated with different tendencies of resistance emergence, with certain groups of antibiotics producing different results, which raises evolutionary questions about the roles of random mutation and induction. Most ARB detected from the Luria–Delbrück Fluctuation Test belong to the Klebsiella, Enterobacter, and Aeromonas genera. This study provides a baseline understanding of the urban freshwater ecosystem status in central Texas and quantitatively examines the degree of resistance emergence.