Normally, thousands of different kinds of microbes lives in the gut – a distinctive mix for each person, and thought to be passed on from mother to baby. The microbes, including many different bacteria, aid digestion and nutrition, appear to help maintain a healthy immune system, and keep order when harmful microbes invade.

Dr Vincent Young and colleagues from the University of Michigan used a sophisticated analysis technique to profile the bacterial communities in the gut allowing them to look for many more kinds of microbes than was possible with more limited methods. The result is a much more complete picture of the diversity of microbes in the gut.

Mice, which normally develop a diverse set of microbes after being born without one, then were given either cefoperazone, a broad-spectrum cephalosporin antibiotic, or a combination of three antibiotics (amoxicillin, bismuth and metronidazole). Both antibiotic treatments caused significant changes in the gut microbial community. However, in the mice given cefoperazone, there was no recovery of normal diversity. In other mice given the amoxicillin-containing combination, the microbiota largely recovered, but not completely.

However, Young’s team found that a little socialising sparked recovery in even the most severely affected mice. Some of the mice given cefoperazone soon recovered normal microbes after an untreated mouse was placed in the same cage. That wasn’t a complete surprise, since mice have a habit of eating the feces of their cage mates and therefore picked up normal gut microbes quickly.

A lesson applicable to humans? In patients with refractory antibiotic-associated diarrhea due to C. difficile, there have been limited trials of treatments using ‘fecal transplants’ to replace lost gut microbiota. Although this is a pretty unpalatable treatment, the clinical response has been quite remarkable.

The study findings suggest that it is really important to use antibiotics only when indicated, especially in people with health problems that might already compromise their gut microbe health. Multiple rounds of antibiotics may also deserve concern.

The findings will guide the group in related work in which mouse models are being used to examine how changes in the microbiota in the gut may influence inflammatory bowel disease and how it develops and progresses adn may provide insights into colitis associated with C. difficile infection. Their laboratory recently published a study that demonstrates that long-term decreases in gut microbe diversity from repeated antibiotics are associated with recurring C. difficile infection in human patients.

Dr Young cautions against assuming that popular probiotics supplements are the answer as each individual’s specific health needs and vulnerabilities have to be considered.

Infection and Immunity, Vol. 77, Issue 6, June 2009

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More research on gut dysbiosis

First Published in June 2009

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