INCREASED ABUNDANCE OF ENTERIC BACTERIA AND ANTIBIOTIC RESISTANCE FOLLOWING RAIN EVENTS IN FLUSHING BAY, NY

Heterotrophic bacteria resistant to tetracycline and ampicillin, two commonly prescribed antibiotics, were assessed in an urban watershed of New York City. Abundance was determined using culture-dependent approaches and diversity was assessed using molecular techniques. Flushing Bay is a heavily urbanized waterbody prone to Combined Sewer Overflows and runoff from surrounding development. Sampling was performed to examine the temporal patterns of antibiotic-resistant microbes under both dry- and wet-weather conditions. The abundances of culturable ampicillin-resistant and tetracycline-resistant bacteria were positively correlated with one another in paired samples and increased following precipitation events. The abundance of the fecal-indicator bacteria, Enterococci, positively correlated with levels of resistant bacteria, suggesting a shared sewage-associated source. This correlation supports use of Enterococcus as an indicator of conditions potentially hazardous for human contact, especially in urban waterbodies designated for recreational use. Analysis of 16S rRNA genes from isolated microbes identified a phylogenetically diverse group of resistant bacteria, including the genera Aeromonas, Pseudomonas, Stenotrophomonas, and Escherichia/Shigella. All of these genera include opportunistic pathogens and have been associated with antibiotic-resistant infections, especially in immuno-compromised individuals. Sequences identified as enteric bacteria were more abundant during wet weather and also represented a greater proportion of resistant sequences compared to non-resistant. This study is the first to document the presence and diversity of antibiotic-resistant bacteria in a New York City watershed and to demonstrate a linkage between the abundance of antibiotic-resistant bacteria and levels of sewage contamination.