Antibiotic Resistance of Indicator Bacteria Isolated from Recycled Vs. Potable Water Distribution Systems.

Recycled municipal wastewater is used in many areas of the U.S. for agricultural irrigation, and there is growing interest in additional direct and indirect potable reuse options. As water reuse infrastructure expands, the potential for within-distribution system microbial regrowth is of increasing concern. In recycled water systems, elevated levels of organic carbon and nutrients, extended water age, intermittent stagnant flow conditions, decay of residual disinfecting agents, and even anaerobic zones may affect the microbial quality of the water at the point of use. This study conducted the first U.S. survey of paired recycled and potable water distribution systems to compare the potential for within-system regrowth and to assess antibiotic resistance of bacterial isolates. Bulk water samples were collected from the recycled and potable water distribution systems of four participating utilities. Samples were collected before treatment, at the point of entry to each distribution system, and at five points of increasing water age throughout the system. Gram-positive and Gram-negative isolates from select water samples were tested for resistance to four commonly prescribed antibiotics. Whole genome sequencing was performed on a subset of the isolates to examine correlations between resistance assessments using cultural vs. molecular methods. Collected data will be analyzed with the goal of identifying resistance levels in recycled vs. potable water systems, and to identify any acute human health risk elucidated by within-system sampling.