In a pregnant primate model, oral administration of L. monocytogenes resulted in stillbirth with isolation of the bacterium from placental and fetal tissues (Smith et al. 2003). When in utero infection occurs, it can precipitate spontaneous abortion. The fetus may be stillborn or die within hours of a disseminated form of listerial infection known as granulomatosis infantiseptica, which is characterized by widespread microabscesses and granulomas that are particularly prevalent in the liver and spleen. In this entity, abundant bacteria are often visible on Gram stain of meconium (Visintine et al. 1977; Larsson and Linell 1979).
More commonly, neonatal infection manifests like group B streptococcal disease in one of two forms (Lorber 1997): (1) early-onset sepsis syndrome, usually associated with prematurity and probably acquired in utero; or (2) late onset meningitis, occurring at about 2 weeks of age in term infants, who most likely acquired organisms from the maternal vagina at parturition. Cases have occurred after cesarean delivery, however, and nosocomial transmission has been suggested.
In early-onset disease, L. monocytogenes can be isolated from the conjunc-tivae, external ear, nose, throat, meconium, amniotic fluid, placenta, blood, and, sometimes, CSF; Gram stain of meconium may show gram-positive rods and provide early diagnosis. The highest concentrations of bacteria are found in the neonatal lung and gut, which suggests that infection is acquired in utero from infected amniotic fluid, rather than via a hematogenous route (Becroft et al. 1971). Purulent conjunctivitis and a disseminated papular rash have rarely been described in neonates with early-onset disease, but clinical infection is otherwise similar to that due to other bacterial pathogens.
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