Qualitative and quantitative differences in normal vaginal flora of conventionally reared mice, rats, hamsters, rabbits, and dogs

We examined quantitatively the vaginal flora of conventionally reared mice, rats, hamsters, rabbits and dogs, species that are widely used as laboratory animals. Vaginal specimens were examined according to the method of analyzing intestinal flora (Mitsuoka's procedure). The total number of bacteria (aerobes and anaerobes) and the prevalence of specific bacteria were determined. The total number of bacteria was highest during estrus and lowest during diestrus or anestrus in mice, rats, hamsters, and dogs. The most predominant bacteria during estrus were streptococci in mice; gram-negative rods (GNR), streptococci, and members of the family Bacteroidaceae in rats; GNR, Bacteroidaceae and gram-positive anaerobic cocci in hamsters, and Bacteroidaceae in dogs. The increase in the total number of bacteria during estrus was caused by an increase of predominant bacteria in the vagina. Aerobes were more predominant than anaerobes in mice, and number of aerobes was comparable to that of anaerobes in rats and dogs. On the other hand, in hamsters, anaerobes were more predominant than aerobes and the total number of bacteria was highest among the laboratory animals (mice, rats, hamsters, rabbits, and dogs). However, in rabbits, bacteria were not isolated from about 90% of the vaginal specimens. Rabbits do not have cyclic reproductive stages and are usually in precoital status in the laboratory. In precoital rabbits, vaginal epithelium manifests few signs of secretion. Therefore, we suspect that the vaginal environment in precoital rabbits is comparable to that during diestrus or anestrus in mice, rats, hamsters, and dogs. These results suggest that the vaginal flora of laboratory animals is influenced by the estrous cycle, and probably by mucous secretion. Our data imply that vaginal flora differ among laboratory animals species, and researchers need to take into consideration the estrous cycle of laboratory animals when studying their vaginal flora.