Ecophylaxis: preventive treatment with gentamicin of rabbit lincomycin-associated diarrhea

In rabbits the oral or parenteral administration of lincomycin result in a severe and usually fatal form of diarrhea. The rabbits treated simultaneously with lincomycin and gentamicin do not present any sign of disease and behave exactly, therefore, as the control subjects. The same occurs in subjects treated with gentamicin alone. In all the subjects which died with diarrhea there was a marked alteration of the intestinal bacterial flora. Among the aerobic bacteria there was an overgrowth of coliforms and less frequently of enterococci, while bacilli were reduced and lactobacilli completely disappeared. Among the anaerobic bacteria, bacteroides and bifidobacteria disappeared and there was an overgrowth of clostridia instead. In rabbits treated contemporaneously with lincomycin and gentamicin, coliforms were absent and the mean number of clostridia was at least one hundred times lower; as in rabbits treated only with lincomycin, enterococci were present in greater number, while lactobacilli, bifidobacteria and bacteroides completely disappeared. Some of the bacteria which are able to overgrow in lincomycin treated subjects, in particular coliforms and clostridia, can be considered potentially pathogenic and their overgrowth could therefore explain the onset of diarrhea. Actually in faecal specimens of rabbits with lincomycin-associated diarrhea, together with the overgrowth of E. coli and clostridia, there is an absence of lactobacilli, bifidobacteria and bacteroides. It is known that these last bacteria contribute, in normal conditions, to maintaining the ecological equilibrium of the intestinal microbial flora. The diarrhea itself can be attributed most likely to the ecological alteration of intestinal microbial flora, with an overgrowth of some potentially pathogenic bacteria and the suppression of others which normally exert an inhibiting effect on the former. It has been suggested to call this form of gentamicin prophylaxis of lincomycin-associated diarrhea 'ecophylaxis', in the sense that it prevents or corrects certain types of ecological alteration of the intestinal microbial flora which lead to diarrhea.