Applicability of Standard Antibiotic Toxicity Tests to the Ambient Aquatic Environment

Abstract

Antibiotics enter the aquatic environment via wastewater and other sources, where they may promote selection of resistant bacteria, and thus add to the global reservoir of antibiotic resistance. Ambient concentrations typically are several orders of magnitude below the lowest observed effect concentration (LOEC) or minimum inhibitory concentration (MIC), which suggests this is unlikely. However, the dissolved organic matter (DOM) concentration in conventional MIC laboratory assays is typically three orders of magnitude higher than in the ambient aquatic environment. Partitioning of antibiotics on DOM could affect their bioavailability making the laboratory MIC values inapplicable to the ambient environment. This question was investigated using laboratory experiments with E. coli, tetracycline and DOM varied over six orders of magnitude. For the DOM concentrations that were able to support significant growth, the calculated MIC endpoint was 1 mg/L. No media effect was observed, which suggests that sorption to MIC test media is insignificant and that the laboratory-determined MIC values are applicable to the ambient environment.

Permanent URL: http://hdl.handle.net/2047/d20002072