Comparison of PCR and culture for detection of Nocardia asteroides in brain specimens from experimentally infected BALB/c mice.

Systemic infection of BALB/c mice with Nocardia asteroides strain GUH-2 results in widespread replication of the organism in the brain, followed by its immune-mediated clearance. The present study compared the sensitivity of polymerase chain reaction (PCR) to bacterial culture for detection of cerebral nocardial infection in this experimental system. Mice (n=4/time point) were administered N. asteroides by intravenous injection, and brain specimens were evaluated for Nocardia by PCR and culture at post-infection days 2, 7, 14 and 21. Nocardia was detected by PCR in all infected animals on post-infection days 2, 7, and 14, and in one of four mice on post-infection day 21; in contrast, the organism was detected by culture only on post-infection days 2 and 7. These findings suggest that PCR may be more sensitive than culture for the detection of low numbers of Nocardia in the brain.