Early acquisition of Pneumocystis carinii in neonatal rats as evidenced by PCR and oral swabs

Abstract

The complete life cycle of Pneumocystis carinii has not been defined, but accumulating evidence suggests that the mammalian host may acquire this organism early in life. In the present study, the initial time of P. carinii acquisition was determined in rats by amplification of P. carinii DNA in oral swabs from seven sets of pups and dams and from fetal tissue obtained by cesarean section of three gravid female rats. DNA extracted from all samples was amplified by using PCR primers directed to the P. carinii mitochondrial large subunit rRNA. Amplicons were produced from 80% (28 of 35) of pups within 2 h after birth; from 97% (34 of 35) after 24 h, and in all of the serially sampled pups by 48 h. No P. carinii amplicons were produced from 48 fetuses or their placentae taken by cesarean section. Thus, P. carinii is acquired almost immediately after birth, and placental transmission occurs rarely, if ever, in rats.

FIG. 1.

Representative oral swab samples taken from one group of pups and their dam at time points ranging from 1 to 2 h to 1 week after pup birth. Oral swab samples were collected from individual rats within 2 h after pup birth (A) and at 24 h (B), 48 h (C), 72 h (D), and 1 week (E) after birth. All panels show amplicons for Rcc (137 bp) and rat globin (400 bp) primer sets. Lanes 1, oral swabs collected from the dam; lanes 2 to 10, oral swabs collected from individual rat pups; lanes 11, positive control (P. carinii DNA, contaminated with rat DNA); lanes 12, negative control (water).

FIG. 2.

Results of PCR, using P. carinii-specific and rat globin-specific primers, of fetal tissue homogenates collected by cesarean section. (A) Rcc primers; (B) primers directed to rat globin. Lanes 1 to 48, results from individual rat fetuses; lanes 49 to 51, internal negative controls (described in Materials and Methods); lanes 52, positive control (P. carinii or rat DNA); lanes 53, negative control (water). These data were generated from several gels that have been used to create this composite figure. All negative controls were negative on each gel, and all positive controls produced appropriately sized amplicons.