Studies on Streptococci

Abstract

The population levels of bacteria in the contents and the walls of the gastrointestinal tract of gnotobiotic rats inoculated with lactic acid bacteria (streptococci, lactobacilli, and bifidobacteria) from humans and rats were determined. Lactobacilli as well as streptococci isolated from rats colonized in the digestive tracts of the gnotobiotic rats at a high population level, characteristically highest in the stomach. On the other hand, in the rats inoculated with human lactic acid bacteria, streptococci were dominant in the lower tract. The human lactobacilli or bifidobacteria did not colonize when the organisms in each genus were inoculated together with streptococci. However, when all three genera were inoculated together, lactobacilli and bifidobacteria colonized. Observations on the species of streptococci showed that the intestinal type of streptococci was found to colonize at a high population level, but the oral type was not. Strains of the same genus of lactic acid bacteria from humans and from rats showed different colonization patterns.The intestinal microflora is known to influence various functions of the host. In our previous papers (3-6), it was reported that activities of some enzymes such as alkaline phosphatase, ,8-glucuronidase, and acid phosphatase in the intestines of rats were influenced by indigenous intestinal microorganisms, for example, streptococci and Escherichia coli. Since bacterial production of lactic acid attracted our attention as one of the characteristics of indigenous intestinal bacteria, we have been studying the distribution and functions of lactic acid bacteria in the host. We reported that lactobacilli control the population levels of other kinds of bacteria in the stomach and the small intestines of rats (11). We also reported that adhesion of lactobacilli to gastric epithelial cells of rats may be an important factor in colonization of the bacteria in the region, that the adhesion may be host specific, and further that some in vitro conditions influence the adhering ability (7,15). Recently, we reported the distribution of fecal streptococci in man (18). We think that 363 364 Y. KAWAI ET AL streptococci are more important members of the lactic acid bacteria than lactobacilli because streptococci are present at a higher population level in the human ileum and large intestine (9, 10). In this paper, the colonization of lactic acid bacteria (streptococci, lactobacilli, and bifidobacteria) isolated from humans and rats in the gastrointestinal tract of gnotobiotic rats is described. MATERIALS AND METHODSBacteria. Bacteria used for injection into germfree rats are listed in Table 1. Suspensions of streptococci and lactobacilli were obtained from Rogosa broth (2) cultures incubated at 37 C for 15 hr. Bifidobacteria were cultured in VL-G broth (1) at 37 C for 15 hr. Bacterial cells were harvested by centrifugation (3,000 rpm, 15 min) and suspended in sterile saline (10 9 cells/rnl). The suspensions of bifidobacteria were prepared under anaerobic conditions. Animals an...