Ampicillin and Gentamicin Resistant Proteus mirabilis from Seawater

Proteus mirabilis, a gram-negative bacterium found in the human gastrointestinal tract flora, is an opportunistic pathogen that causes community acquired and nosocomial infections including urinary tract infections (UTI), further resulting in sepsis and systemic inflammatory response syndrome (SIRS) when left untreated.  P. mirabilis is also intrinsically resistant to tetracycline and nitrofurantonin and increasingly gaining resistance to additional clinically relevant antibiotics. Despite the large amount of information on P. mirabilis in the clinical setting, little is known of its antimicrobial resistance in the environment. In this study, the objective was to (1) determine whether the aquatic environment harbors P. mirabilis bacteria that are resistant to clinically relevant antibiotics and (2) to understand the distribution of the resistant strains. To test this hypothesis, freshwater and saltwater was collected within Orange County, California from creeks, beaches, rivers and streams. Water from these locations was filtered, and pure bacterial isolates were obtained by streaking onto CHROMagar Orientation. Protein was then extracted from the bacterial isolates and the species identified using matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry.  Antibiotic resistance and susceptibility was measured by performing a Kirby-Bauer disk diffusion assay following the Clinical and Laboratory Standards Institute (CLSI) protocols. Overall, twenty P. mirabilis strains were isolated from the aquatic environment of which 70% were found in saltwater while 30% were found in freshwater. The resistance profiles of the P. mirabilis isolates were as follows: 20% amoxicillin-clavulanic acid (100% found in saltwater), 40 % ampicillin (50% saltwater), 20% cefoxitin (33% saltwater), 5% ciprofloxacin (100% freshwater), 25% gentamicin (80% saltwater), and 21% sulfamethoxazole-trimethoprime (75% saltwater). The distribution of antibiotic resistance varied considerably such that 67% of the resistant strains were found in saltwater while 33% in freshwater. Our results indicate that seawater serves as a reservoir for P. mirabilis that is resistant to the clinically relevant antibiotics: ampicillin, and gentamicin. Furthermore, PCR and other molecular techniques are necessary to identify the genes that confer resistance and gain in-depth understanding of resistant P. mirabilis strains. Supported by the MBRS NIH Grant GM-55246.