Studies on the establishment of multi-drug-resistant strain BIO-4R of Streptococcus faecalis in the intestinal tract of germ-free mice. Bacterial interaction and effect of antibiotics.

Germ-free ICR mice were mono- or dicontaminated with a multi-drug-resistant strain BIO-4R of Streptococcus faecalis (BIO-4R) and Escherichia coli 026 : K60 (E. coli) and administered aminobenzyl penicillin (ABPC). BIO-4R was established in the intestinal tract at a level of 10(8) viable cells per gram of stool on the fourth day following oral inoculation and the BIO-4R population was stably maintained thereafter. The drug resistance of BIO-4R remained unchanged in the intestinal tract of gnotobiotes throughout the experiment. Highly resistant cells of E. coli were isolated from the feces of some dicontaminated mice after ABPC administration. However, it seems that the high resistance of these E. coli is not due to the transfer of resistance of BIO-4R to E. coli. All animals given a large amount of BIO-4R (10(8) cells) per os survived throughout the study period of two weeks without symptoms.