While most bacteria involved in dentoalveolar infection are highly susceptible to penicillin, some Prevotella strains exhibit resistance to this agent through the production of beta-lactamase. The production of beta-lactamase by Prevotella spp. is in turn associated with the expression of the genes cfxA and cfxA2. The aim of the present study was to determine the prevalence of cfxA and cfxA2 in Prevotella strains by use of real-time PCR and to assess the performance of this molecular method for the direct detection of the genes in 87 clinical samples (pus and root canal exudates) from dentoalveolar infection. Production of beta-lactamase by each isolate was determined using a nitrocefin disk. beta-Lactamase production was seen in 31% of Prevotella isolates, while all isolates of other species were beta-lactamase negative. The penicillin resistance of isolates strongly correlated with the production of beta-lactamase. Real-time PCR was found to detect the cfxA and cfxA2 genes from at least five cells per reaction mixture (5 x 10(3) CFU/ml of pus). Using real-time PCR, the presence of cfxA and cfxA2 was evident for all 48 beta-lactamase-positive Prevotella strains. In contrast, neither beta-lactamase-negative Prevotella (n = 91) or non-Prevotella (n = 31) strains were positive for the genes. In this study, 31 of the 87 samples yielded beta-lactamase-positive Prevotella results, and cfxA and cfxA2 were detected in all 31 samples. Of the 56 culture-negative samples, 8 (14%) were positive for cfxA and cfxA2 by the real-time PCR. This sensitive and specific molecular method offers a rapid clinical test for aiding in the selection of an appropriate antibiotic for treatment of dentoalveolar infection. Although penicillin remains largely effective in the treatment of dentoalveolar infection, beta-lactamase-stable antibiotics should be considered in cases in which beta-lactamase-positive Prevotella strains are involved.