Intestinal flora during the first months of life: new perspectives.

Increasing awareness that the human intestinal flora is a major factor in health and disease has led to different strategies to manipulate the flora to promote health. The complex microflora of the adult is difficult to change in the long term. There is greater impact of diet on the infant microflora. Manipulation of the flora particularly with probiotics has shown promising results in the prevention and treatment of diarrhoea and allergy. Before attempting to change the flora of the infant population in general, a greater understanding of the gut bacterial colonisation process is required. The critical stages of gut colonisation are after birth and during weaning. Lactic acid bacteria dominate the flora of the breast-fed infant. The formula-fed infant has a more diverse flora. The faeces of the breast-fed infant contain mainly acetic and lactic acid whereas the formula fed-infant has mainly acetic and propionic acid. Butyric acid is not a significant component in either group. The formula-fed infant also has higher faecal ammonia and other potentially harmful bacterial products. The composition of the microflora diversifies shortly before and particularly after weaning. The flora of the formula-fed infant develops more quickly than that of the breast-fed infant. Before embarking on any strategy to change the flora, the following questions should be considered: Should we retain a breast-fed style flora with limited ability to ferment complex carbohydrates? Can pro- and prebiotics achieve a flora with adult characteristics but with more lactic acid bacteria in weaned infants? Are there any health risks associated with such manipulations of the flora?