Impact of Integrated Fish Farming on Antimicrobial Resistance in a Pond Environment

Abstract

Integrated fish farming combines livestock production with fish farming. Animal manure is shed directly into a fish pond as fertilizer and supports the growth of photosynthetic organisms. The livestock, mainly chickens and pigs, is often fed feed containing growth promoters. In this study we investigated the impact of integrated fish farming on the levels of antimicrobial-resistant bacteria in a pond environment. One integrated broiler chicken-fish farm was studied for 2 months immediately after the start of a new fish production cycle. A significant increase over time in the resistance to six different antimicrobials was found for the indicator organism Acinetobacter spp. isolated from composite water-sediment samples. The initial resistance levels prior to the new production cycle were 1 to 5%. After 2 months the levels of resistance to oxytetracycline and sulfamethoxazole reached 100%, and the levels of resistance to ciprofloxacin were more than 80%. The long-term effects of resistance on integrated farming were studied on seven additional farms. The resistance levels were particularly high among Enterococcus spp. and were also high among Acinetobacter spp. isolated from water-sediment samples compared to the resistance levels at four control farms. In conclusion, integrated fish farming seems to favor antimicrobial-resistant bacteria in the pond environment. This could be attributed to the selective pressure of antimicrobials in the pond environment and/or to the introduction of antimicrobialresistant bacteria from animal manure. Potential risks to human health were not addressed in this study and remain to be elucidated.

Impact of Medicated Feed on the Development of Antimicrobial Resistance in Bacteria at Integrated Pig-Fish Farms in Vietnam

“…3) were most likely associated with the use of these antimicrobials, and the subsequent excretion of resistant bacteria and their presence could have been favored due to selection pressure exerted by the presence of antimicrobials or antimicrobial residues (12). It is unlikely that the resistant bacteria may have acted as donors of quinolone resistance genes upon release into the fish ponds, as resistance to quinolones are rarely transferred horizontally.…”

“…Overall, a higher prevalence of bacterial resistance was found in integrated farms than that in control farms (12). That study was impaired by a lack of knowledge about the type and amount of antimicrobials added to the animal feed as growth promoters and therapeutics at the farms studied (12). Enterococcus spp.…”

“…The use of animal manures as fertilizers of aquaculture ponds is practiced widely in Southeast Asia (12). Livestock manure is disposed of into fish ponds, and the release of nutrients supports the growth of photosynthetic organisms (10).…”

“…The discharge of animal wastes containing antimicrobial residues and resistant bacteria into fish ponds may favor selection and growth of antimicrobial-resistant bacteria, with a potential risk of resistance genes being disseminated into a wide range of aquatic environmental bacteria (12). A previous study in Thailand of the impact of integrated aquaculture on the development of antimicrobial resistance in the pond microflora demonstrated a significant increase of resistance among ubiquitous Acinetobacter spp.…”

“…Enterococcus spp. and Escherichia coli are common in environments contaminated by human and animal feces and therefore are often used as indicators of fecal contamination and to monitor antimicrobial resistance (12,13,14).…”