Effect of Antibiotics in the Intestinal Tract of Gnotobiotic Mice

In relation to the effect of an oral antibiotic agent on intestinal bacterial flora, we wanted to study the influnce by the region of absorption and concurrently existing bacteria using germfree mice. First we produced the following four kinds of mice: 1) Monocontaminated mice by E. coli; 2) Dicontaminated mice by E. coli and Lactobaccillus; 3) Tricontaminated mice by E. coli, Lactobacillus and Streptococcus; and 4) Multicontaminated mice by E. coli, Lactobacillus, Streptococcus and Bacteroides. Then, Ampicillin and Gentamicin were administered to the mono-, di-, tri-. and multicontaminated mice respectively and to multicontaminated mice, Ciclacillin, Caphalexin, and Erythromycin were also administered and the fluctuation in the number of each kind of bacteria in feces and each region of the intestinal tract was measured. 1) From the above results we assumed that, in the upper region of the small intestine, Ciclacillin and Cephalexin were absorbed well, whereas the absorptions of Ampicillin and Erythromycin were not too good, and Gentamicin was hardly absorbed in the intestinal tract. 2) With respect to the effect of intestinal bacteria of an agent which was not absorbed from the intestinal tract such as Gentamicin, it seemed the time necessitated to pass through the intestinal tract was an important influencing factor. 3) With regard to the difference in the effect of an antibiotic agent where other bacteria concurrently existed, there was almost no difference observed in the effect of Ampicillin and Gentamicin administered to dicontaminated mice by E. coli and Lactobacillus. On the other hand, in the mono-, tri-, and multicontaminated mice, a tendency of decreasing number of sensitive strains was observed depending on the degree of absorption. In other words, the role of Lactobacillus in dicontaminated mice seemed very interesting. 4) Regarding the tolerance, Ampicillin resistant E. coli was found in both the mono-, and tricontaminated mice. 5) In our experiments at this time, we used gnotobiotic mice produced by establishing specific kinds of bacteria in germfree mice so that such experiments may indicate the result on the neonatal period in a sense and we think there would be disagreement in some aspects with the result obtained using conventional mice having a formation of bacterial flora. However, at the same time our result might indicate the correlation between antibiotic agents and bacteria in vivo.