Antibiotic Resistant Enterococcus in Aquatic Environments

Enterococci are gram-positive bacteria that are responsible for several clinically significant infections such as urinary tract infections, bacteremia, bacterial endocarditis, diverticulitis, and meningitis. This bacterium occupies the intestines, and the two most common enterococci species found in humans are Enterococcus faecalis (90-95%) and Enterococcus faecium (5-10%). Enterococci are the second most common cause of nosocomial infections in the United States, and they are the third most prevalent pathogen in causing nosocomial bloodstream infections. Enterococci are intrinsically resistant to multiple antibiotics including penicillins, cephalosporins, aminoglycosides, and most fluoroquinolones. Enterococci’s ability to gain resistance to various antibiotics is a growing concern within the medical community, however it is unknown whether resistance can only be acquired in healthcare facilities. In this study, we predict aquatic environments to be a natural reservoir for antibiotic resistance in enterococcus. In order to test our hypothesis, water samples from local sources were collected, filtered, and the bacteria was acquired through a selective media and isolated through streaking. Proteins were then extracted from the bacteria and isolates identified through MALDI-TOF mass spectrometry. Antibacterial resistance was determined through the Kirby-Bauer disk diffusion test in accordance to the Clinical and Laboratory Standards Institute (CLSI) protocols. After analyzing 2010 and 2011 results, it was found that E. faecalis and E. faecium isolates occurred equally frequent in the environment (28% and 26%) as compared to the large disparity in humans. The enterococcus isolates were found to be resistant to several clinically relevant antibiotics such as ampicillin and nitrofurantoin. Ampicillin is used to treat meningitis caused by enterococcus, and nitrofurantoin is used to treat urinary tract infections. Of the 107 enterococcus isolates that were tested against ampicillin and nitrofurantoin, 20% of the isolates were resistant to ampicillin and 7% were resistant to nitrofurantoin. Despite there being many studies on the increasing number of antibiotic resistant enterococcus, essentially all of these studies are performed in the clinic. This is one of the first studies to test for antibiotic resistant enterococcus in aquatic environments. Although shadowed by the number of enterococcus isolates susceptible to antibiotics, enterococcal resistant isolates are found in the environment and continue to pose a threat to humans. Supported by NIH-MBRS-IMSD Grant GM-55246.