Nutrition plays a key role in maintaining the balance of the intestinal microflora. Malnutrition disturbs the ecological barrier and induces histological damage. We evaluated modifications induced by renutrition with nonfat milk (NFM) and Lactobacillus casei administration (for 2 days) on the bacterial gut population and structural and ultrastructural gut modifications in malnourished mice. Balb/c mice suffering from a malnutrition process immediately after weaning (for 21 days) were divided into four groups and were given NFM for 0, 7, 14, and 21 days. Another group was treated in a similar way, but after different periods of NFM administration, mice in this group received L. casei for two consecutive days. All experimental animals were sacrificed by cervical dislocation, and both the microflora and the histological structure of the intestine were studied. In malnourished animals, a decrease in the numbers of Lactobacillus and anaerobic microorganisms was observed, whereas there was an increase in the number of Enterobacteriaceae. In animals treated with NFM and NFM plus L. casei, we could observe an important improvement in the microflora in the small and large intestines but no differences between both treatments. Structural and ultrastructural studies showed a slight improvement 7 days after treatment with NFM, and for 14 and 21 days after renutrition, the mice showed normal intestinal villi, whereas the additional feeding with L. casei for two consecutive days, after different periods of renutrition, yielded an earlier improvement (7 days).

The dominant species were Streptococcus viridans and Staphylococcus saprophyticcus, followed by S. epidermidis, Lactobacilli and S. cohnii I which were present on every studied days but at different proportions.This paper is the first part of a research topic investigating the protective effect of the indigenous flora against pathogens using the mice as an experimental model.

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