Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2002
Publication Date: 3/3/2003
Citation: Poole, T.L., Genovese, K.J., Knape, K.D., Callaway, T.R., Bischoff, K.M., Nisbet, D.J. 2003. Effect of subtherapeutic concentrations of tylosin on the inhibitory stringency of a mixed anaerobe continuous-flow culture of chicken microflora against Escherichia coli O157:H7. Journal of Applied Microbiology. 94:73-79.
Interpretive Summary: Bacteria that cause diseases in livestock and poultry are among the most serious problems faced by farmers today. Drugs that kill bacteria are called antibiotics. Antibiotics are often included in the feed of livestock and poultry. This is done to speed growth and improve the health of food producing animals. There are a number of side effects associated with the use of antibiotics in feed. One of them is the killing of beneficial gut bacteria. The beneficial gut bacteria protect animals from disease causing bacteria. These disease causing bacteria also include bacteria that cause food poisoning in people. Using a system in the laboratory we were able to show that an antibiotic was inhibitory to beneficial bacteria while allowing a bacterium that causes food poisoning to stay. Our work is important because it identifies a possible way to make our food supply safer from harmful bacteria. It could help in reducing the amount of antibiotics that farmers use, and may decrease the chance of people consuming disease causing bacteria in their food.
Technical Abstract: Aims: The aim of this study was to determine the effect of subtherapeutic concentrations of tylosin on a mixed anaerobic continuous-flow fermentation culture of chicken gastrointestinal microorganisms (CCF), and to determine if these concentrations would allow persistence of Escherichia coli O157:H7 in CCF. Methods and Results: CCF was treated with tylosin at 10.0, 20.0 and 40.0 ug ml**-1. Tylosin treatment resulted in a significant (P< 0.0001) decrease in total volatile fatty acids (VFAs) from a mean concentration of 101 ± 10.8 umol ml**-1 in control cultures to 32.0 ± 6.3 and 40.2 ± 9.6 umol ml**-1 in 10 and 40 ug ml**-1 treated cultures, respectively. Untreated CCF challenged with E. coli O157:H7 cleared the challenge microorganism in seven days at a rate of 0.96 log10 cfu ml**-1 d**-1. In contrast, E. coli O157:H7 persisted in all tylosin treated cultures. Conclusions: In the presence of tylosin, E. coli O157:H7 was able to persist in the CCF culture. The significant decrease in the production of VFAs may have been a contributing factor. Significance and Impact of the Study: The use of low-level, growth promoting antimicrobials may compromise the ability of normal microflora that serve as a natural host defense against infection.