Primary endodontic infection is caused by microorganisms colonizing the necrotic pulp tissue. In general, primary infections are mixed and predominated by anaerobic bacteria. Although more than 200 microbial species have been isolated/detected from infections of endodontic origin, a more restricted group composed of15-30 species has been implicated as candidate endodontic pathogens (Siqueira 2002). Such putative pathogens belong to the genera Treponema, Bacteroides, Porphyromonas, Prevotella, Fusobacterium, Peptostreptococcus, Eubacterium and Campylobacter.
Campylobacter gracilis is a nonmotile, nonspore forming, anaerobic Gram-negative rod with a formate- and fumarate-requiring metabolism. Cells are small and straight,0.4 mm wide and 4-6 mm long, with round ends. The G + C content of the DNA is 43-47 mol% (Tanner et al.1981,1992).This species was proposed and described by Tanner et al. (1981), as Bacteroides gracilis. Vandamme et al. (1995) analysed the cellular fatty acids, respiratory quinones and proteins of B. gracilis, and compared the features with the corresponding chemotaxonomic features of its closest relatives, the Campylobacters. Their results and previously published data for genotypic and phenotypic characteristics were used to reconsider the classification of this species, transferring it to the genus Campylobacter.
Campylobacter rectus is a small, nonspore forming, asaccharolytic, microaerophilic Gram-negative rod capable of motility via a single polar flagellum. Cells are frequently straight, 0.5 mm wide and 4 mm long, but may occasionally appear curved or helical. Regarding its metabolism, formate or hydrogen from several oral microorganisms serves as electron donors, whilst nitrate or fumarate from arpartate-producing microorganisms serves as electron acceptors. The G ÑŽ C content of the DNA is 42-46 mol% (Tanner et al. 1981, 1992). The species was described by Tanner et al. (1981), as Wolinella recta, and further transferred to the genus Campylobacter (Vandamme et al.1991).
Campylobacter gracilis and C. rectus have been recovered from different forms of periodontal diseases and claimed to have a potential pathogenic role in such diseases (Rams et al.1993,Tanner et al. 1997, 1998, Kamma et al. 2000, Macuch & Tanner 2000). Studies have also isolated/detected these Campylobacter species from endodontic infections in variable prevalence values (Ranta et al. 1988, Sundqvist et al.1989,1998, Sundqvist 1992, Gomes et al.1996, Le Goff et al.1997, Siqueira et al. 2000b, 2001b).
Because these species are not always easily identified by conventional phenotype-based identification procedures, it is possible that their prevalence has beenunderestimated in primary endodontic infections. Molecular technologies, particularly the polymerase chain reaction (PCR)method, over come many of the problems associated with traditional phenotype-based identification methods. PCR has been widely used to identify microbial species that are difficult or impossible to cultivate, and strains difficult to identify due to a phenotypically convergent or divergent behavior (Relman 1993, 1999). The PCR methodology has the highest detection rate between the microbiological identification methods, and under optimized conditions also shows high specificity (McPherson & Moller 2000).The nested PCR (nPCR) technique is a modification of the PCR technology that involves a first amplification reaction of a DNA sequence with one set of primers followed by reamplification using a second set of primers complementary to smaller specific sequences within the first PCR product. nPCR can show increased sensitivity and even improved specificity when compared with single PCR (Dieffenbach & Dveksler 1995, McPherson & Moller 2000, Jordan et al. 2001).
This study aimed to investigate the prevalence of C. gracilis and C. rectus in primary endodontic infections associated with different forms of periradicular diseases using a sensitive identification method – the nested PCR.