Bacteroides forsythus prtH genotype in periodontitis patients: occurrence and association with periodontal disease.

Bacteroides forsythus has been described as a periodontopathogen and its presence in the subgingival plaque can lead to periodontal disease. Recently, a cysteine protease designated as prtH was isolated and characterized from B. forsythus ATCC 43037. The purpose of this study was to determine the prevalence and the association of the prtH gene of B. forsythus with periodontal disease. A total of 160 subgingival plaque samples were assayed with the polymerase chain reaction method using oligonucleotide primers targeting the prtH and the 16S rDNA genes of B. forsythus. Primers targeting the 16S rDNA gene of B. forsythus were used to determine the occurrence of the bacteria in the subgingival plaque samples at baseline. At baseline, B. forsythus was detected in 78 out of 86 (91%) diseased sites and 33 out of 74 (45%) healthy sites studied. Among the 86 diseased sites examined, 73 sites (85%) were colonized by the bacteria with the prtH genotype. In sites of the periodontally healthy, 7 out of 73 (10%) possessed B. forsythus with the prtH genotype. The results obtained suggested strong association of the prtH gene of B. forsythus with adult periodontitis. Although this bacterial species was detected from about half of the periodontally healthy samples, only a fraction of these subjects possess the bacteria strain with the prtH genetic subtype. We propose the use of the prtH gene as an alternative to the more widely used 16S rDNA gene of B. forsythus, for a more accurate determination of the prevalence of periodontal health and disease in epidemiological studies and clinical screening.