title: Dynamics of Listeria monocytogenes type 4b infection in pregnant and infant rats.
abstract: In order to examine the dynamics of perinatal listeriosis, we established a rat model of infection using a strain of Listeria monocytogenes type 4b isolated from a human newborn infant. When injected subcutaneously, the median lethal dose (LD50) to the organism was lower for pregnant than nonpregnant animals (10(8) vs 10(9) colony forming units [cfu]). Susceptibility was greatest on the 16th day of gestation (67% mortality) as was the likelihood that the offspring had generalized infection (50%). In contrast, all five pregnant rats injected on the 9th day of gestation survived. None of the five went on to have a litter, thus suggesting that there was intrauterine death. The LD50 for infant (3-day-old) rats was 6 X 10(5) cfu; that for juveniles (13-day-old) 2.5 X 10(7) cfu (p less than 0.005). No differences were seen between infant or juvenile rats in the number of viable bacteria in homogenized liver, spleen and lung or in blood at 1 or 3 days after a weight-adjusted intraperitoneal bacterial challenge. However, 5 days after challenge, viable organisms were decreased in all of these sites for the juveniles while they were increased for the infants (p less than 0.001). Polymorphonuclear (PMN) and mononuclear cells appeared in the peritoneum in similar concentrations for infant and juveniles one day after intraperitoneal challenge. At 5 days the number of mononuclear cells was significantly greater for juveniles compared to infants (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000375:Aging; D000818:Animals; D005260:Female; D008088:Listeriosis / Q000276:immunology*; D009000:Monocytes; D009504:Neutrophils; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000276:immunology*; D051381:Rats