Aquatic Aeromonads: A Survey of Antibiotic Resistance to Ciprofloxacin and Sulfmatheoxazole-Trimethoprim

Aeromonas spp. are gram-negative, facultatively anaerobic, oxidase-positive, rod-shaped bacteria that are virtually ubiquitous in the environment. Isolated from nearly every environmental niche where bacterial ecosystems exist, this plethora of environmental sources from which aeromonads can be encountered culminates in constant interactions between the genus Aeromonas and humans. Although initially regarded only as pathogenic among cold-blooded animals, recent discoveries expose aeromonads as agents responsible for a variety of infections in both immunouncompromised and immunocompromised patients. Aeromonas clinical infections vary from life threatening conditions such as septicemia, necrotizing fasciitis, and myonecrosis to milder conditions such as gastrointestinal tract syndromes, wound and soft tissue infections, blood-born dyscrasis, and a panorama of less frequently encountered illnesses and infections. This study hypothesizes that the aquatic environment is a reservoir for Aeromonas species resistant to clinically relevant antibiotics, particularly Sulfamethoxazole-Trimethoprim and Ciprofloxacin. Water was filtered from selected freshwater and saltwater creeks, rivers, and beaches in Southern California and placed in various selection media. Following identification using MALDI-TOF spectrometry, the antibiotic resistance profiles of the isolated bacterial colonies were determined using the Kirby-Bauer disk diffusion test in accordance with standards outlined by the Clinical Laboratory Standards Institute (CLSI). The species identified are listed in order of decreasing environmental abundance as follows: Aeromonas culicola, A. hydrophila, A. caviae, A. bestiarum, and A. veronii. Aeromonads collected demonstrate resistance to a variety of clinically relevant antibiotics including Piperacillin (18 isolates), Sulfamethoxazole-Trimethoprim (17 isolates), Amikacin (10 isolates), Ciprofloxacin (9 isolates), Gentamicin (8 isolates), Nitrofurantoin (6 isolates), Cefotetan (5 isolates), Ceftazidime (5 isolates), and Meropenem (3 isolates). Furthermore, among the 9 isolates resistant to the floroquinolone Ciprofoxacin, 7 of the isolates were resistant to the synthetic antifolate Sulfamethoxazole-Trimethoprim, indicating a striking pattern of co-resistance among these antibiotics, both of which are used extensively as clinical treatments for Aeromonas infections. The presence of resistance among aeromonads to clinically relevant antibiotics, particularly Sulfamethoxazole-Trimethoprim and Ciprofloxacin, implicates aquatic environments as reservoirs harboring antibiotic resistance among Aeromonas species. Supported by MBRS NIH Grant GM055246.