The susceptibility of germ-free, oestradiol-treated, mice to Mycoplasma hominis

Conventionally reared female BALB/c mice, rendered susceptible to Mycoplasma hominis infection of the genital tract by treatment with oestradiol, have increased numbers of endogenous vaginal bacteria. The latter was reflected by the occurrence of bacterial growth in 95 (65.5%) of 145 cultures undertaken to isolate M. hominis from oestradiol-treated mice, but in only seven (4.8%) of 146 cultures from untreated animals. In addition, larger numbers of bacteria were seen in vaginal smears from oestradiol-treated mice than from untreated ones. Furthermore, abscesses developed in the genital region of 27 (17%) of 155 oestradiol-treated mice but in none of 50 that were untreated. However, such proliferation of the endogenous vaginal bacteria was not necessary for colonisation of the vagina by M. hominis. This was determined by showing that six germ-free, oestradiol-treated BALB/c mice given 2.5 x 10(5) ccu of M. hominis intravaginally became colonised vaginally for at least 14 days, with multiplication and spread of the organisms to the upper genital tract and elsewhere, whereas six similar untreated mice given the same inoculum remained uninfected.