Does the frequency of Prevotella intermedia increase during pregnancy?

Introduction: The former Bacteroides intermedius, currently including Prevotella intermedia and Prevotella nigrescens, has been associated with hormone-induced pregnancy gingivitis. The aim of the present longitudinal study was to determine whether only P. intermedia or P. nigrescens, or both species, are involved in the demonstrated microbial shift during pregnancy.

Methods: Subgingival plaque and saliva samples, collected from 30 healthy pregnant women and 24 healthy non-pregnant women as their controls, were examined for the presence of pigmented gram-negative anaerobes. Altogether 2628 isolates were preliminarily identified as P. intermedia sensu lato, based on phenotypic testing. Their further identification was performed by using a 16S ribosomal DNA-based polymerase chain reaction (PCR).

Results: A mean of 8.3 P. intermedia sensu lato isolates from each subject/sampling was examined. During the second trimester, the mean number of P. intermedia sensu lato in plaque increased along with increasing signs of pregnancy gingivitis, and then both decreased. After delivery, gingival inflammation still decreased while the number of P. intermedia sensu lato transiently increased both in plaque and saliva. In the present study, the vast majority of isolates (95.3%) proved to be P. nigrescens and 2.5% were P. intermedia. The remaining 2.2% of the isolates could not be identified with PCR as P. intermedia or P. nigrescens. The corresponding percentages in the control population were 94.2%, 5.5%, and 0.3%.

Conclusion: In the oral cavity of relatively young women without periodontitis, P. nigrescens, unlike P. intermedia, is a frequent finding. Conceivably, pregnant women harbor increasing numbers of P. nigrescens associated with pregnancy gingivitis.