Increased demand for fresh water has led to interest in reusing wastewater effluent for landscape and agricultural irrigation. However, treated wastewater effluent often contains residual antibiotics which, through the chronic exposure of irrigation, can lead to the propagation of antibiotic resistance in environmental bacteria and increase the risk of severe food-borne illness outbreaks. This work examined how continuous exposure to ciprofloxacin (CIP), utilizing a 96-well plate sequencing batch reactor format, may increase the observed antibiotic resistance in the common soil bacterium, Pseudomonas putida. This work demonstrated that chronic exposure over a 3-month period to ppb and ppt levels of CIP resulted in the development of CIP-resistant Pseudomonas putida cells. The minimum inhibitory concentration (MIC) rose from a baseline of 1 ppm to up to 16 ppm, which is above clinical dosages. The higher the CIP concentration, the more quickly the resistance was developed and the greater the resistance. Removal of the CIP resulted in a decrease in MICs to near background levels. However, the reintroduction of CIP resulted in the immediate increase in MICs to the levels previously observed after months of exposure. The results of this work suggests that chronic exposure to environmental relevant concentrations of CIP may result in the development of drug-resistant bacteria and that this resistance may be maintained or quickly regained between growing seasons.

Development of antibiotic resistance in Pseudomonas putida chronically exposed to environmentally relevant concentrations of ciprofloxacin

251st National Meeting (2016)

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