Experimental genital mycoplasmosis: time of infection influences pregnancy outcome

Abstract

Genital infection of rats with Mycoplasma pulmonis causes adverse pregnancy outcome and can result in in utero spread of infection to the fetus. The current study was designed to determine whether the stage of pregnancy when infection occurs influences pregnancy outcome. Rats were inoculated with 3 ؋ 10 7 CFU of M. pulmonis at 10 days prior to breeding (؊10) or at gestational day (gd) 11 or 14 and were necropsied at gd 11, 14, or 18 or within 24 h of parturition (term). Control rats received sterile broth. M. pulmonis was isolated from the placenta, amniotic fluid, or fetal tissues only from rats infected prior to breeding (P < 0.001). All infected rats had significantly more loss of pups than did control rats (P < 0.006), but rats infected prior to breeding or at the beginning of the third trimester (gd 14) were much more likely to have fetal losses. Rats infected in the early second trimester after implantation (gd 11) did not experience severe losses. Litter sizes, total litter weight, and individual pup weight from all infected rats, regardless of gestational stage when infected, were significantly smaller than those of control rats (P < 0.001). On the basis of the results of this study, we conclude that the time of infection plays a major role in determination of pregnancy outcome and spread of infection from the genital tract to the respiratory tract. Mycoplasma pulmonis is a common pathogen of mice and rats in many conventionally maintained colonies (3-5, 14). In addition to its role in respiratory disease, M. pulmonis is responsible for genital infections and infertility (5, 7, 17, 18). It has been estimated that M. pulmonis infection decreases rat birth rate 50 to 100% (5, 17). We have demonstrated the adverse impact of genital infection on pregnancy outcome in experimentally infected Sprague-Dawley (SD) rats (17). Genital infection prior to breeding resulted in increased fetal resorptions and an increased number of dams with no liveborn pups (17). Furthermore, individual pup weight, litter size, and litter weight were also decreased in infected rats. In a second study, we demonstrated that M. pulmonis could invade the placenta, breach the placental barrier, and establish an amniotic fluid infection by gestational day (gd) 14 (18). M. pulmonis was isolated from the oropharynx as well as lungs of fetuses at gd 18, confirming in utero transmission (18). Histological evidence was compatible with an active infection characterized by placentitis, amnionitis, and occasional mild fetal bronchopneumonia (18). M. pulmonis is an ideal candidate for a model of intrauterine infection. First, it is a naturally occurring disease. Second, the infection can be established by intravaginal inoculation, without requiring extensive manipulation of the animal. Third, the natural course of disease in the rat is similar to that predicted for human pathogens, i.e., an ascending infection that breaches the placental barrier and establishes as an amnionitis. Finally, a strong database exists for normal reproductive physiology and...

Genital Mycoplasmosis in Rats: A Model for Intrauterine Infection1

“…Pregnancy outcome was adversely affected by vaginal infection with M. pulmonis prior to breeding or at gestational day (Gd) 14. 52,65 Infected rats had significantly smaller litter sizes at Gd 18, P 50.01, and at term, P5 0.004. Litter size was defined as the number of pups delivered at term, including stillborn pups, or the number of potentially viable fetuses at Gd 11, 14 or 18.…”

“…Previous studies have been performed with rats infected prior to breeding. 52,65,66 However, during natural genital infections, exposure also can occur during pregnancy. Therefore, it was of interest to see if time of infection influenced pregnancy outcome.…”

“…Therefore, it was of interest to see if time of infection influenced pregnancy outcome. 65 Rats were intravaginally inoculated with 10 7 colony-forming units (CFU) M. pulmonis. Rats infected 10 days prior to breeding (− 10) were necropsied at Gd 11, 14, 18, and within 24 hr of parturition (term).…”

“…In utero transmission did not occur in any group except those rats infected prior to breeding. 65 Mycoplasma pulmonis was isolated from the genital tract in ] 50% of rats at each of the time points. Spread to the respiratory tract was variable.…”

Variations in the surface proteins and restriction enzyme systems of Mycoplasma pulmonis in the respiratory tract of infected rats

“…The rat pathogen M. pulmonis strain X1048 (Brown and Steiner, 1996) was propagated in mycoplasma broth and analysed for cfu on mycoplasma agar as described previously (Dybvig et al, 1998;Shen et al, 2000). Strains of M. pulmonis used as controls for PCR and Western analyses include the VsaA-producing strain KD735-15 (Shen et al, 2000) and strain KD273, a filter clone of strain KD735-16 (Dybvig et al, 1998) that produces VsaB.…”