PCR-BASED DETECTION OF BACTERIAL-DNA AFTER ANTIMICROBIAL TREATMENT ISINDICATIVE OF PERSISTENT, VIABLE BACTERIA IN THE CHINCHILLA MODEL OF OTITIS-MEDIA

Purpose: Bacterial deoxyribonucleic acid (DNA) has been previously det ected by polymerase chain reactions (PCR) in a significant percentage of culturally-sterile pediatric middle-ear effusions. The current stud y was designed to determine whether this represents the existence of v iable bacteria or the persistence of residual DNA in the middle-ear cl eft. Materials and Methods: The middle-ear cavities of two sets of chi nchillas were inoculated with either: 1) 100 colony-forming units (CFU ) of live Haemophilus influenzae, 2.2 x 10(6) CFU of pasteurized Morax ella catarrhalis, and 1000 ng of DNA (>10(8) genomic equivalents) from Streptococcus pneumoniae; or 2) 100 CFU of live S pneumoniae, 2.2 x 1 0(6) CFU of pasteurized M catarrhalis and 1000 ng of purified DNA from H influenzae. Animals were treated with ampicillin for 5 days beginni ng on day 3. A single-point longitudinal study design was used for sam pling to eliminate the possibility of contamination. Results: No DNA w as detectable from the heat-killed bacteria or the purified DNA after day 3. However, DNA from the live bacteria persisted through day 21, e ven though all specimens were culture-negative following the initiatio n of antimicrobial therapy. Conclusion: These findings indicate that p urified DNA and DNA from intact but nonviable bacteria do not persist in the middle-ear cleft in the presence of an effusion, even following high copy inoculation. in contrast, antibiotic-treated bacteria persi st in some viable state for weeks as evidenced by the differential abi lity of the PCR-based assay systems to detect the live bacteria, but n ot detect the heat-killed organisms. Copyright (C) 1996 by W.B. Saunde rs Company.