Exposure of the grass shrimp, Palaemonetes pugio, to antimicrobial compounds affects associated Vibrio bacterial density and development of antibiotic resistance.
- 1National Oceanic and Atmospheric Administration, National Ocean Service, National Centers for Coastal Ocean Science, Center for Coastal Environmental Health and Biomolecular Research, Charleston, South Carolina, 29412.
- 2Department of Biology, College of Charleston, Charleston, South Carolina, 29412.
Antimicrobial compounds are widespread, emerging contaminants in the aquatic environment and may threaten ecosystem and human health. This study characterized effects of antimicrobial compounds common to human and veterinary medicine, aquaculture, and consumer personal care products [erythromycin (ERY), sulfamethoxazole (SMX), oxytetracycline (OTC), and triclosan (TCS)] in the grass shrimp Palaemonetes pugio. The effects of antimicrobial treatments on grass shrimp mortality and lipid peroxidation activity were measured. The effects of antimicrobial treatments on the bacterial community of the shrimp were then assessed by measuring Vibrio density and testing bacterial isolates for antibiotic resistance. TCS (0.33 mg/L) increased shrimp mortality by 37% and increased lipid peroxidation activity by 63%. A mixture of 0.33 mg/L TCS and 60 mg/L SMX caused a 47% increase in shrimp mortality and an 88% increase in lipid peroxidation activity. Exposure to SMX (30 mg/L or 60 mg/L) alone and to a mixture of SMX/ERY/OTC did not significantly affect shrimp survival or lipid peroxidation activity. Shrimp exposure to 0.33 mg/L TCS increased Vibrio density 350% as compared to the control whereas SMX, the SMX/TCS mixture, and the mixture of SMX/ERY/OTC decreased Vibrio density 78-94%. Increased Vibrio antibiotic resistance was observed for all shrimp antimicrobial treatments except for the mixture of SMX/ERY/OTC. Approximately 87% of grass shrimp Vibrio isolates displayed resistance to TCS in the control treatment suggesting a high level of TCS resistance in environmental Vibrio populations. The presence of TCS in coastal waters may preferentially increase the resistance and abundance of pathogenic bacteria. These results indicate the need for further study into the potential interactions between antimicrobials, aquatic organisms, and associated bacterial communities.
KEYWORDS:Vibrio; antibiotics; resistance; shrimp; toxicity; triclosan
- PMID: 25348372; DOI:10.1002/tox.22060
- Over 200,000 metric tonnes of antibiotics used annually for human and veterinary medicine, livestock production, aquaculture
- Antimicrobial compounds are detected in surface waters worldwide, with potential to affect aquatic ecosystem & human health
- Vibrio bacteria are an abundant bacterial genus in marine ecosystems. They are found to have high frequencies of antibiotic resistance in the environment. Many Vibrio sp. are pathogenic and pose a threat to human health, such as V. vulnificus (wound infections), V. parahaemolyticus (seafood poisoning), and Vibrio cholerae (food/drinking water contamination).
- In the environment, sub-inhibitory levels of antimicrobials have led to antibiotic resistance. Multiple antibiotic resistance (MAR) in Vibrio has been found in coastal water & sediment. MAR has been detected in dolphins, sharks, seals, seagulls, etc. Due to presence of drug-resistant ‘superbugs’, 23,000 people die each year in U.S. from antibiotic resistant infections. Transfer of antibiotic resistance from environment to humans is a potential concern.
- The objective of this study was to determine the effects of selected antimicrobial compounds on grass shrimp survival, grass shrimp cellular stress responses, grass shrimp bacterial densities, and development of bacterial antibiotic resistance.
- The antimicrobials selected were 1) sulfamethoxazole (SMX), a sulfonamide antibiotic used in humans, dogs, horses, cattle, and pigs, which acts by inhibiting folic acid synthesis; 2) erythromycin (ERY), a macrolide antibiotic used in humans, dogs, cats, cattle, and chickens, which acts by inhibiting protein biosynthesis of the 50S ribosome; 3) oxytetracycline (OTC) a tetracycline antibiotic used in humans, dogs, cats, cattle, sheep, pigs, and aquaculture, which acts by inhibiting aminoacyl-tRNA binding to 30S ribosomal A; and 4) triclosan (TCS), a chlorinated biphenyl ether added as an antimicrobial in consumer products and is also a registered pesticide, which acts by inhibiting fatty acid synthesis.
- No effect on shrimp survival at the concentrations tested
- Increased lipid peroxidation activity with TCS exposure
- Decrease in shrimp Vibrio population with SMX and OTC/ERY/SMX mixture
- Increase in shrimp Vibrio population with TCS exposure
- Development of MAR with SMX exposure
- Vibrio isolates displayed resistance to TCS in the control treatment suggesting a high level of TCS resistance in environmental Vibrio populations
- Exposure to antibiotic mixture did not lead to MAR
- The presence of TCS in coastal waters may preferentially increase the resistance and abundance of pathogenic bacteria
- Need for improved regulation of antimicrobial use and disposal