Submitted to: Antimicrobial Chemotherapy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 24, 2006
Publication Date: July 7, 2006
Citation: Poole, T.L., McReynolds, J.L., Edrington, T.S., Byrd II, J.A., Callaway, T.R., Nisbet, D.J. 2006. Effect of flavophospholipol on conjugation frequency between Escherichia coli donor and recipient pairs in vitro and in the chicken gastrointestinal tract. Journal of Antimicrobial Chemotherapy. 58:359-366. Interpretive Summary: Antibiotics have been in use for fifty years to combat bacterial infections. When antibiotics were first discovered many thought bacterial diseases would be eradicated; however, this has not happened. In fact, some disease causing bacteria are reemerging due to the development of resistance to antibiotics. The use of antibiotics among food-producing animals is believed to have created a reservoir of antimicrobial resistant microflora. One of the problems is that bacteria can share or transfer resistance genes by a process called conjugation. Conjugation occurs when a bridge is formed between two bacterial cells and a circular piece of DNA called a plasmid migrates across the bridge. After this process is completed the recipient cell that acquired the plasmid will be resistant to the same antibiotics as the donor cell. A poultry and livestock feed additive called flavophospholipol has been shown to block conjugation between some bacteria in laboratory experiments. This study put donor and recipient pairs in chickens that were fed flavophospholipol at different experimental doses to determine if flavophospholipol blocked conjugation in the gastrointestinal tract of chickens. Although flavophospholipol blocked conjugation between the donor and recipient pairs in the laboratory, it didn’t work in chickens.
Technical Abstract: Objectives: To examine the ability of flavophospholipol to inhibit bacterial conjugation between Escherichia coli donor and recipient pairs in vitro and in day-of-hatch chickens. Methods: In vitro donor cultures were incubated in the presence of 0, 2, 4, 8, 16, 32 and 64 mg/L flavophospholipol during primary overnight mono-cultures only, secondary conjugation cultures only, or throughout primary and secondary cultures. Transconjugants were selected using oxytetracycline naladixic acid. Treatment groups A-G (n=20) of day-of-hatch broiler chickens received 0, 2, 4, 8, 16, 32 and 64 g/ton flavophospholipol, respectively in their feed throughout the experiment. On day four, all treatment groups were given 0.25 mL of donor and recipient E. coli at 7.0 and 9.0 log10 cfu/mL, respectively. On day ten, the birds were euthanized and the cecal contents were cultured on selective medium (oxytetracycline and naladixic acid). Results: A dose dependent reduction in transconjugant populations was observed in vitro when flavophospholipol was present in the secondary conjugation culture. The susceptibility profiles of transconjugants obtained from in vitro studies were identical to the predicted profile of the donor and recipient combination. There was no significant difference (P less than or equal to 0.05) in the number of transconjugants isolated from chickens among any of the flavophospholipol treatment groups when compared to the controls. The susceptibility profiles of chicken transconjugants suggested acquisition of naturally occurring plasmids. Conclusions: Flavophospholipol strongly inhibited conjugation in vitro, but did not prevent recipient E. coli from acquiring resistance determinants in vivo.