Aggregatibacter actinomycetemcomitans and its relationship to initiation of localized aggressive periodontitis: longitudinal cohort study of initially healthy adolescents

Abstract

Aggregatibacter actinomycetemcomitans is frequently associated with localized aggressive periodontitis (LAP); however, longitudinal cohort studies relating A. actinomycetemcomitans to initiation of LAP have not been reported. A periodontal assessment was performed on 1,075 primarily African-American and Hispanic schoolchildren, ages 11 to 17 years. Samples were taken from each child for A. actinomycetemcomitans. A cohort of 96 students was established that included a test group of 38 A. actinomycetemcomitans-positive students (36 periodontally healthy and 2 with periodontal pockets) and 58 healthy A. actinomycetemcomitans-negative controls. All clinical and microbiological procedures were repeated at 6-month intervals. Bitewing radiographs were taken annually for definitive diagnosis of LAP. At the initial examination, clinical probing attachment measurements indicated that 1.2% of students had LAP, while 13.7% carried A. actinomycetemcomitans, including 16.7% of African-American and 11% of Hispanic students (P = 0.001, chi-square test). A. actinomycetemcomitans serotypes a, b, and c were equally distributed among African-Americans; Hispanic students harbored predominantly serotype c (P = 0.05, chi-square test). In the longitudinal phase, survival analysis was performed to determine whether A. actinomycetemcomitans-positive as compared to A. actinomycetemcomitans-negative students remained healthy ("survived") or progressed to disease with attachment loss of >2 mm or bone loss (failed to "survive"). Students without A. actinomycetemcomitans at baseline had a significantly greater chance to remain healthy (survive) compared to the A. actinomycetemcomitans-positive test group (P = 0.0001). Eight of 38 A. actinomycetemcomitans-positive and none of 58 A. actinomycetemcomitans-negative students showed bone loss (P = 0.01). A. actinomycetemcomitans serotype did not appear to influence survival. These findings suggest that detection of A. actinomycetemcomitans in periodontally healthy children can serve as a risk marker for initiation of LAP.

FIG. 1.

Aggregatibacter actinomycetemcomitans serotypes: relationship to site of recovery and to ethnicity. (A) Example of PCR assay for serotype identification. Lane labels indicate serotype. The sizes (in base pairs) of the molecular weight standards run are shown on the left. Fragments were run on a 5% polyacrylamide gel. (B) Histogram of A. actinomycetemcomitans serotypes in relation to ethnicity of A. actinomycetemcomitans carrier. Serotype c is significantly greater in the Hispanic children who carry A. actinomycetemcomitans (P = 0.05). No differences were seen in serotype distribution in African-American children who carry A. actinomycetemcomitans. (C) Histogram of percentage of subjects who had A. actinomycetemcomitans and the specific serotypes of A. actinomycetemcomitans found in relation to the ethnicity of the A. actinomycetemcomitans carrier. Note that the overwhelming majority of students did not carry A. actinomycetemcomitans (No Aa).

FIG. 2.

Survival plots of healthy A. actinomycetemcomitans-positive (test group, n = 38) compared to healthy A. actinomycetemcomitans-negative (control group, n = 58) students at initial screening visit and how their periodontal status progressed over the recall period. The x axis shows the time in days after the screening visit, and the y axis shows the proportion of students who remained healthy and had no disease over the recall period. (A) Students who survived and thus did not have two 5-mm pockets at recall. The A. actinomycetemcomitans-negative group (control group) is seen in the top curve, while the A. actinomycetemcomitans-negative group (test group) is seen in the lower curve. Of those students who never developed two 5-mm pockets over the recall period, 65% had no A. actinomycetemcomitans, while only 10% of those who had A. actinomycetemcomitans failed to develop two pockets. Therefore, 90% of those who had A. actinomycetemcomitans did develop two pockets (P = 0.0001). (B) Students who survived and thus did not have three 5-mm pockets at recall. The control group is seen in the top curve, and the test group is seen in the lower curve. The number of students in the A. actinomycetemcomitans-negative group who developed three 5-mm pockets was only 10%, while over 80% of those in the A. actinomycetemcomitans-positive group developed three pockets (P = 0.0001). (C) Students who survived and thus did not have pockets greater than 6 mm with attachment loss 2 mm or greater at recall. The control group is seen in the top curve, and the test group is seen in the lower curve. Of those who never developed one 6-mm pocket, over 85% had no A. actinomycetemcomitans. Of those who did develop one or more 6-mm pockets with attachment loss, over 85% had A. actinomycetemcomitans (P = 0.0001). (D) Students who survived and thus did not have bone loss at recall. The control group as seen in the top curve cannot be discerned because there was no bone loss throughout the recall period. The test group is seen in the lower curve. Only those students in the test group had bone loss (P = 0.01).

FIG. 3.

Survival plot comparing students who harbored serotype a, b, or c and how these serotypes related to two or three 5-mm pockets. The top curve shows the plot for the A. actinomycetemcomitans-negative controls. Plots for A. actinomycetemcomitans-positive subjects carrying strains of serotype a, b, or c are shown in the remaining curves. No difference in survival analysis was seen when the strains were compared.