Susceptibility of the female reproductive tract of mice to Tyzzer's organism.

Susceptibility of the reproductive tract of ICR adult female mice to Tyzzer's organisms was examined by intravenous and intravaginal inoculation at various stage of pregnancy. After intravenous inoculation, the uterus was most severely affected when inoculation was made at the midpregnancy. Severe involvement of the uterus was also seen after intravaginal inoculation made either at late-pregnancy or shortly before and after parturition. While non-pregnant female mice were less susceptible to intravenous or intravaginal inoculation, the growth of organisms in the uterine epithelium was recognized after intrauterine inoculation. In 4CS adult female mice showing a constant 4-day-estrous cycle the endometrium was found to be the most susceptible at the estrus phase. Such difference in susceptibility of the female reproductive tract depending upon stage of pregnancy and estrous cycle might be related to metabolic changes of the endometrium controlled by sex hormones, whereas increased blood circulation and modified immune response during pregnancy and estrous cycle might be also involved.