Posted on Fri, Jun. 17, 2005
SCIENCE FILE | THEA SINCLAIR
Good bacteria killed bad without antibiotics
Recently, I was invited to accompany Andrea, our veterinarian daughter, to the Georgia Veterinary Medical Association’s annual meeting. Andrea was going to present her current research at the Poultry Diagnostic Lab at University of Georgia.
Her work dealt with fighting bacterial infection in chickens without using antibiotics. Instead of antibiotics, Andrea implied other bacteria, using a principle called competitive exclusion. Before I can explain her project, I need to discuss animal-bacterial associations.

Many different species, including humans, have important relationships with micro-organisms. For example, termites have protozoa in their intestines that allow them to digest the cellulose in the wood they eat.
Likewise, grazing animals such as cows and horses have bacteria in their stomachs that help in plant digestion. About 70 percent of insects in the wild have bacteria called Wolbachia living within them.
In one study of fruit flies, infected male fruit flies that mated with uninfected female flies were unable to reproduce. On the other hand, female flies infected with Wolbachia that mated with infected or uninfected males did produce young.
Apparently, the Wolbachia must be present on the egg surface or inside the eggs for a new generation to occur. As a result, the number of infected members will increase in the population. Wolbachia can also change the ratio of males to females in an insect population by killing males with the bacteria but not females.
Another interesting animal-bacteria relationship exists between a type of squid and the luminescent bacteria Vibrio. Unlike the Wolbachia relationships, the bacteria are not passed to the next generation through the egg.
Rather, they are obtained from the environment by newly hatched juveniles. On land, this transmission is not difficult. Chickens, for example, get bacteria by pecking at everything in their environment, including chicken litter.
However, the Vibrio bacteria represent less than 0.1 percent of the total bacterial present in the surrounding seawater. The squid produce mucus that is positioned above cells of a specialized light organ that are available for the bacteria to colonize.
Hairs on the skin surface beat and create a current that pulls the bacteria near the mucus. Somehow, only the correct bacteria enter the skin cells of the light organ, and these cells change, making a home for the bacteria to stay. For the rest of the squid’s life, these bacteria produce light and, in exchange, get nutrition and a dwelling place.
Most people are aware that humans have bacteria that live in our intestine. Some produce vitamin K, necessary for blood clotting. One would think that a healthy immune system would wipe out these bacteria, but actually, the resident bacteria are important. They cause the intestinal lining to produce chemicals that fight invading bacteria. When humans take antibiotics for infections, some of these beneficial bacteria are killed as well. Some people ingest probiotics (harmless bacteria), available at health food stores, or eat yogurt while taking antibiotics in order to try to quickly replace the beneficial bacteria.
Evidence is growing that medical problems, such as allergies, asthma and inflammatory bowel disease, may in some cases result from the lack of proper development of the interactions between beneficial residential microbes and host tissues.
So what does all of this have to do with chickens? In the chicken industry today, the growers try to prevent the chickens from being infected with bacteria like Salmonella, E. coli, and Listeria.
To prevent infection, most chickens are given antibiotics. Some consumers are opposed to antibiotics in their meat, because they fear it will cause increased numbers of antibiotic-resistant strains of bacteria.
So there is a move among chicken producers to stop antibiotic use, but at the same time protect the public from disease.
Andrea’s research involved placing probiotics in the food and water of newly hatched chickens. She let them grow for five weeks and then checked the chickens for the presence of indicator bacteria, in this case, antibiotic-resistant E. coli.
She repeated the experiment with five successive flocks of chickens in the same chicken house and compared their microflora with a control group. Her results suggested that the bacteria could be reduced by the presence of good bacteria, because two similar species cannot live in the same location and compete for limited resources.
However, more statistical analysis and repetition with other bacteria besides E.coli are needed before a final conclusion can be made.