Antibiotic Resistance Profiles of Enterobacter spp. Isolated From Fresh and Saline Aquatic Environments

Increasing concern over antimicrobial resistance proves a leading topic regarding global public health. As a leading source of nosocomial respiratory infections, Enterobacter is prone to acquired antibiotic resistance. Normally effectively treated with either a course of flouroquinalones or carbabenems for extreme cases; resistant strains have become troublesome to treat. In clinical settings E. cloacae as well as E. asburiae, the most prevalent strains, are responsible for a wide array of infections including bacteremia, respiratory tract infections, skin and soft tissue infections, urinary tract infections, and endocarditis. Patients hospitalized for more than two-weeks, those undergoing invasive procedures in the past 72 hours, and patients requiring a central venus catheter are at the greatest risk of developing an Enterobacter infection. Most Enterobacter species harbor or eventually develop antibiotic resistance during antimicrobial therapy making identification of the source of antibiotic resistance crucial.  The aim of this study was to delineate the role of the aquatic environment as a natural reservoir for antibiotic resistance where selective pressure by synthetic antimicrobials may be reduced. To study this phenomena bacterial isolates were collected over a span of two years from specific freshwater or seawater locations. Selective antibiotic media was utilized in conjunction with repeated culturing to narrow down potentially resistant isolates. Antibiotic resistance was evaluated via Kirby-Bauer Disk Suceptibility Tests in accordance with CLSI standards. Genus and species identification was achieved via organic solvent protein extraction and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). Of the isolates collected 75.5% originated from freshwater environments while the remaining 24.5% originated from saltwater environments. Of the total isolates collected 37.6% were identified as E. cloacae while 33.7% identified as E. asburiae. Results suggest resistance among broad spectrum antibiotics. For instance 79.2% of isolates were resistant to Cefoxitin and 71.4% were resistant to Erthyromycin. Among antibiotics typically used to target Enterobacter 10.8% resistance was found to Piperacillin, 8.3% resistance to Tetracyclin, 3.1% resistance to Amikacin, and no resistance was found to Ciprofloxin. The data suggests that aquatic environments may naturally harbor antibiotic resistance. Resistance was found in all of the 13 antibiotics tested with the exception of Ciprofloxin.  Supported by the MBRS NIH Grant GM-055246.