Scientists have shown for the first time how antibiotics can predispose the gut to avoidable infections that trigger bowel disease in mice.
The researchers from The University of Manchester in the UK also showed that substances derived from fibre prevent this damage to the gut, suggesting a high fibre diet could be useful when taken during and after a course of antibiotics.
The study, which appears in the journal Science Translational Medicine, tested broad spectrum antibiotics on mice to assess their impact on the gut's microbiota, the community of microbes that live in the gastrointestinal tract.
After a week long course of antibiotics, a harmful immune reaction started that lasted at least two months, an equivalent of many years in humans, said the researchers.
The immune reaction meant that significantly fewer beneficial bacteria which make 'short chain fatty acids', which are good for the gut, grew back.
However, short chain fatty acids, produced by the fermentation of dietary fibre by the microorganisms which live in the gut, could prevent the harmful immune response.
"Epidemiological evidence already links antibiotics given to babies and young children, when the immune system is still developing, to inflammatory bowel disease, asthma, psoriasis and other inflammatory diseases later in life," said Elizabeth Mann from The University of Manchester.
"However, until now it has been hard to determine cause and effect, especially with the time lag between taking the antibiotics and the development of disease later in life," she said.
This study helps explain the link through understanding the biological processes involved.
"Inflammatory bowel disease in particular has multiple causes but one of the triggering factors in many people has been infections such as Salmonella or E coli," said Mann.
"We show that after antibiotics, mice are more susceptible to these types of infections, and do not mount the proper immune response to clear the infection," she said.
The gut is the largest source of bacteria in the body, where trillions of harmless bacteria critical for maintaining a healthy immune system live.
However, when antibiotics are taken orally, they deplete a massive community of bacteria in the intestines.
Not all patients taking antibiotics will get these diseases, and that is because most people need a genetic predisposition to get them, researchers said.
It is very important that patients continue their antibiotics as these drugs are critical in clearing bacterial infections that can persist and cause serious health problems if left untreated, they said.
"But what we are saying is that antibiotics must only prescribed when absolutely needed for bacterial infections.
"Antibiotics, for example, are useless against viral infections such as those that cause the common cold, flu and many chest infections," she said.