Abstract:
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.
