Recovery of the gut microbiota in ampicillin-treated mice is dependent on the environment

Ampicillin is commonly applied in rodents to induce a temporary depleted microbiota (“temporary germ-free period”), and so our aim was to elucidate to which extent bacteria are eliminated or just temporarily suppressed. Two weeks ampicillin treatment in mice, immediately after weaning, induced a state comparable to a germ-free state. The treatment reduced innate cytokine signal in the ileum, but increased the proportion of CD8+ T-cells and NKT-cells and decreased regulatory T-cells in the gut associated lymph tissue. A novel observation was that four weeks after treatment caeca were still significantly enlarged. After a re-colonisation period, recovery of the gut microbiota (GM) was dependent on the environmental conditions, and while some GM members were able to recover and even dominate the community, their abundance was differently configured in isolator and conventionally housing, and far from the original state of the untreated mice. Indeed, temporary ampicillin treatment is appropriate for inducing a temporary germ-free-like state and it may have the desired impact on the immune system. Yet, rather than a temporary GM depletion, data suggest that upon termination of ampicillin treatment GM is non-recoverable, and the implications and interpretations for disease development are highly dependent on the environmental surroundings.