Resistance to antibiotics on the increase in intestinal bacteria in animals: Study

Anne-Mette R. Grønvold has through her doctoral research shown that resistance to antibiotics is on the increase in intestinal bacteria in animals as a direct result of antibiotic treatments. The antibiotics also alter the composition of bacteria in the intestines. These discoveries provide more knowledge about the undesirable effect of antibiotic treatments and are of comparative interest as regards other animals and humans.

Grønvold studied the intestinal bacteria in healthy dogs undergoing an ordinary course of antibiotics. After a few days of the treatment, the E. coli bacteria in the intestines developed a resistance to several different types of antibiotics. Grønvold also discovered changes in the composition of intestinal bacteria. The use of antibiotics is thought to contribute to the proliferation of resistance to antibiotics and is also the most common cause of disturbances in intestinal flora in humans. Adult humans and animals have more bacteria in their intestines than the number of cells making up their entire bodies, and these intestinal bacteria constitute an ecological community that is essential for the health of the individual. Worldwide, nearly 50% of all antibiotics are used for veterinary purposes. Grønvold's thesis shows that the intestinal bacteria of animals are affected by antibiotics when it comes to both resistance and ecological balance.

The thesis also studies the effect of a real treatment of antibiotics (penicillin) on bacteria in the intestines of horses and calves. Penicillin is considered to be one of the "mildest" types of antibiotics available. After a few days' treatment, the E. coli bacteria in the intestines of nearly all the animals in the study became resistant to several types of antibiotics, compared to their state before the start of the treatment. The study also revealed changes in the composition of these animals' intestinal bacteria.

Antibiotics are essential to treat infections, but when bacteria become resistant, the treatment does not work. A course of antibiotics affects all bacteria, not just those that are the cause of disease. Resistance can spread between ordinary intestinal bacteria and disease-producing bacteria, and between bacteria from animals and bacteria from humans. It is therefore important to use antibiotics in the correct way and only when necessary. This will minimise the problem of resistance, so that the antibiotics available still work when they are needed and also in order to maintain a healthy bacterial flora in the intestines.

Cand.med.vet. Anne-Mette Grønvold presented her doctoral thesis on 26th March 2010 at The Norwegian School of Veterinary Science (NVH). The thesis is entitled: "The impact of antibiotic exposure on fecal microbiota of animals".