Growth promotion and gut microbiota: insights from antibiotic use.

Antibiotics have been proposed as supplements in re-feeding programmes for malnourished children. A review of paediatric literature showed that growth promotion by antibiotics, when it was observed, was mostly mediated by its anti-infective properties. Despite the widespread use of antibiotics as growth promoters in animal rearing, the available evidence again points to the suppression of infections as the underlying mechanism. Under controlled hygienic conditions, growth promotion was frequently not observed. Models for 'sub-inhibitory' antibiotic effects on gut bacteria have been proposed, and direct antibiotic effects on host physiology are accumulating. Human gut microbiota analyses in malnourished children (restricted to stool as convenience samples) displayed developmental immaturity of the gut microbiota and growth deficits that were only transiently ameliorated by nutritional interventions. These studies need to be complemented by microbiota analysis in the upper small intestine where bacterial overgrowth, frequently reported in people of the developing world, may directly compete with nutrient absorption by the human host. So far, however, the available medical and veterinary literature suggests that the growth promoting effect of antibiotics mostly works through prevention of infection and a concomitant decrease of the caloric burden of an inflammatory response.