Simple Model of Tetracycline Antibiotic Resistance in Aquatic Environment: Accounting for Metal Coselection

Abstract

Relatively high concentrations of antibiotic-resistant bacteria are often found in the anthropogenically impacted aquatic environment. This is an emerging concern, and it is not clear which mechanism is responsible: external input, selection by antibiotics, or coselection by metals. To explore these hypotheses, a simple mechanistic mathematical model is developed, which includes state variables for antibiotic and metal toxicants, susceptible and resistant bacteria, and particulate and dissolved organic matter (DOM). The toxicants partition to solids and DOM. Bacteria growth is limited by DOM, susceptible bacteria are inhibited by toxicants, and resistant bacteria incur a metabolic cost of carrying the resistance. Tetracycline resistance in the Poudre River in Colorado is considered as a case study. The model is used to predict the concentration of resistant bacteria, and the output is compared with observations from the literature. External input and selection by tetracyclines cannot explain the observed density of resistant bacteria. Comparison of observed ambient concentrations and bacteria chronic toxicity values suggests that Cu, Zn, and Se may exert significant toxicity on the susceptible bacteria. Model simulations with Cu and Zn reproduce the magnitude and general spatial pattern of the observations, which shows that coselection by those metals is plausible; Se does not exert sufficient toxicity. Coselection of antibiotic resistance by metals may be significant, considering the widespread pollution of surface waters by metals.