The Aquatic E. coli Resistance Profile; An analysis of their resistance against CIP and SXT

With antimicrobial resistance increasing to staggering percentages, Escherichia coli has become an immense cause of distress to the scientific community. Antibiotic resistance in E. coli, the microbe responsible for 90% of UTIs (Urinary Tract Infections), over 250,000 cases of foodborne illness in the United States annually and, most recently, the 2011 outbreak in Germany which resulted in the death of over 30 people, has been well documented worldwide. As a result of the proliferation of antibiotic resistance, E. coli infections have become increasingly difficult to treat. Although the prevailing hypothesis suggests that clinical overuse of antibiotics provides a selection for resistance, the environment may be a reservoir for such resistance. The aquatic environment, with presumably significantly lower amounts of selection for resistance than a clinic, should not harbor resistance to antibiotics unless it successfully acts as a pool for bacteria to sustain the genes they acquire from the clinic.  Consequently, our lab hypothesized that environmental E. coli should bear resistance to the antibiotics most often prescribed to treat them. Freshwater and seawater samples were collected from a variety of locations and filtered. The bacteria were then isolated via selective media and streaking on chromagar. The bacteria, identified by means of protein extraction and MALDI-Time of Flight mass spectrometry, were tested for antibiotic resistance using the Kirby Bauer disk diffusion assay. All methods were completed in accordance with Clinical Laboratory Standards Institute (CLSI) protocol. Interestingly, environmental bacteria bear significant antibiotic resistance and E. coli resistance was extensive and widespread. The E. coli harbored resistance to every antibiotic they were tested against, which encompassed a range of classes including aminoglycosides, beta-lactams, sulfanilamides and fluoroquiolones. Shockingly, multidrug resistance was predominant with most isolates being resistant to 4-7 antibiotics. Most notably, the bacteria were highly resistant to ciprofloxacin and sulfamethoxazole-trimethoprime, with 44% and 47% resistance respectively. In support of our hypothesis, these antibiotics are of the most prescribed treatments to E. coli infections. Furthermore, a pattern of coresistance may be present between the two antibiotics as sulfamethoxazole-trimethoprime resistant bacteria having a 63% chance of being resistant to ciprofloxacin. Because ciprofloxacin and sulfamethoxazole-trimethoprime are often administered together, coresistance is also supportive of our hypothesis. The environmental E. coli’s extensive and multi-drug resistance profile, as well as their high resistance to the antibiotics prescribed to treat them advocates the environment as a site for further research and exploration.

Supported by NIH-MBRS-IMSD Grant GM-55246.