Another longitudinal study by Höglund Åberg et al. (2014) [pdf] has linked the development and progression of periodontal attachment loss in teenagers with the highly leukotoxic clone of Aggregatibacter actinomycetemcomitans, JP2, in Ghana. It confirms several previous reports by Haubek et al. on adolescents in Morocco (see her PhD thesis here [pdf]) in that JP2 is strongly associated with the onset and progression of aggressive periodontitis, a term which is noticeably avoided by Höglund Åberg et al. in her present paper.
A random sample cohort of students from public and private schools in Greater Accra, Ghana’s capital, had been recruited in 2009. The mean age was 13.2 yr with a standard deviation of 1.5 yr. At follow-up after 2 yr, 397 participants (79.4%) showed in 2011. Periodontal probing was done at the “mesiobuccal [sic] aspect of the mesial and distal surfaces of all fully erupted teeth (except third molars). At baseline and follow-up, attachment loss was calculated as the difference between the distance from the gingival margin to the cemento-enamel junction and the recorded probing pocket depth measurement. Several subgingival plaque samples were collected with paper points for PCR analysis (including determination of the 530 bp deletion in the leukotoxin promoter region pointing to JP2) and cultivation. Only presence or absence of A. actinomycetemcomitans was determined, not its quantity nor the presence of other bacteria.
Disease status at the individual level (case definition) was set at interproximal attachment loss of 3 mm or more in one or more sites in the dentition. Individuals were defined as having progressing disease if they showed one or more sites with a progression of attachment loss of 3 mm or more.
In an extension of a previous report in 2007 , Fine et al. (2013) shed more light last month on the microbiological cause of localized aggressive periodontitis in African Americans and Hispanics. In the new report  of the more interesting longitudinal part of the study, 134 periodontally healthy teenagers (mean age 12-13 yr) had been followed for more than 2 years. Sixty-three subjects harboring Aggregatibacter actinomycetemcomitans in sugingival plaque and/or buccal swab samples had been matched with 71 subjects in which that particular organism could not been found. Twenty-three subjects developed one (first molar) site  with a 6 mm or deeper pocket in combination with 2 mm or more attachment loss. Twenty of these harbored A. actinomycetecomitans at the time of screening. Among the eight subjects who developed two or more (first molar) sites with a pocket depth of at least 6 mm and 2 mm or more attachment loss (thus fitting the Löe & Brown “soft tissue” definition of localized aggressive periodontitis ), all were A. actinomycetemcomitans-positive. Likewise, all 16 subjects who developed alveolar bone loss (identified on standardized bitewing radiographs) harbored A. actinomycetemcomitans.
Among those subjects who developed (according to the definition by Löe and Brown ) localized aggressive periodontitis, seven had been subjected to subject level microbial assessment of pooled samples prior to pocket development and attachment using the 300 taxa of HOMIM (human oral microbe identification microarray). In comparison, ten healthy subjects (five with A. actinomycetemcomitans and five without) served as healthy controls. While healthy controls had higher prevalence of species of the Streptococcus, Actinomyces, Veillonella, Gemella, Granulocitella, Fusobacterium and Campylobacter genera, in those who developed localized aggressive periodontitis, A. actinomycetemcomitans, Filifactor alocis, Treponema socranskii, Tannerella forsythia, Porphyromonas gingivalis, Eubacterium nodatum, Eubacterium infirmum, Eubacterium brachy, Selenomonas sputigena, Prevotella intermedia, and certain unnamed taxa of the Peptostreptococcaceae, Lachnospiracea, and Desulfobulbus genera were among the prominent named species with increased prevalence in subjects prior to development of disease as compared to subjects who remained healthy.
Site-specific microbial assessments using HOMIM were done on all 16 subjects who went from periodontal health to bone loss at a specific tooth site (in total 18 sites). HOMIM analyses were done six months prior to bone loss and at the time when bone loss was detected. Further molar sites in these subjects which remained healthy (i.e., did not develop alveolar bone loss) were also studied, typically three in each subject. Four microbial species had highly elevated DNA probe levels in HOMIM in sites prior to subsequent bone loss, namely A. actinomycetemcomitans, F. alocis, P. gingivalis, and Streptococcus parasanguinis. A group of three Veillonella spp. was also highly elevated while several other species were elevated to a lesser extent in sites prior to bone loss. In sites which stayed healthy, the Fusobacterium cluster and Veillonella dispar were highly elevated. In an attempt to use these site-specific data for a diagnostic tests, it turned out that the presence of a combination of A. actinomycetemcomitans, F. alocis, and S. parasanguinis yielded 89% sensitivity and 99% specificity for subsequent bone loss in these 16 subjects.
It had long been claimed that Aggregatibacter actinomycetemcomitans is strongly associated with localized aggressive periodontitis. In particular, A. actinomycetemcomitans has even been involved in the pathogenesis of aggressive periodontitis. Later it had been realized that this bacterium occurs frequently also in other forms of periodontitis and even gingivitis. And, other bacteria, such as Porphyromonas gingivalis, may be involved in the pathogenesis of both localized and generalized aggressive periodontitis.
One of the upcoming issues of Periodontology 2000 is dedicated to all aspects of, what has turned out, very controversial aggressive periodontitis. Eija Könönen at Turku University and I had been asked to scrutinize the voluminous literature on the microbiology of aggressive periodontitis . The following is a brief summary of the role of A. actinomycetemcomitans as a causative agent and new findings of open-ended molecular techniques regarding the microbiome of localized and generalized aggressive periodontitis.
Criteria for Causality
Sir Bradford Hill had described about 50 years ago criteria for possible causal relationship of certain risk factors for complex chronic diseases (Hill 1965), see here [pdf]. These criteria ultimately proved that smoking causes some forms of lung cancer. Among them, strength of association (including consistency and specificity), temporality of events (the causal factor has to be present before the onset of the disease) and experimental evidence (intervention trials) are of great importance as is for instance the biological gradient (dose-response relationship), while plausibility, coherence with laboratory findings, and analogy are not, or not so much .
Recently, Howick et al. (2009) have re-arranged Hill’s criteria , see here [pdf], putting much emphasis on direct evidence for a causal relationship which comprises the size of the effect (after adjusting for possible confounding), the appropriate temporal and/or spatial proximity (the cause precedes the effect and the effect occurs after a plausible interval; the cause occurs at the same site as the intervention), and dose-responsiveness and reversibility. What they call mechanistic evidence (evidence for biological, chemical, or mechanical mechanisms of action; and parallel evidence (coherence, replicability, similarity) would therefore not suffice to prove causality.
Methods and Results (I)
A systematic literature search was done in PubMed using the following focused question:
“Do prospective studies exist which may indicate a causal relationship between Aggregatibacter actinomycetemcomitans and the development of periodontitis at young age?”
Search terms were: (“actinobacillus actinomycetemcomitans”[MeSH Terms] OR (“actinobacillus”[All Fields] AND “actinomycetemcomitans”[All Fields]) OR “actinobacillus actinomycetemcomitans”[All Fields] OR (“aggregatibacter”[All Fields] AND “actinomycetemcomitans”[All Fields]) OR “aggregatibacter actinomycetemcomitans”[All Fields]) AND (“aggressive periodontitis”[MeSH Terms] OR (“aggressive”[All Fields] AND “periodontitis”[All Fields]) OR “aggressive periodontitis”[All Fields]) AND (“longitudinal studies”[MeSH Terms] OR (“longitudinal”[All Fields] AND “studies”[All Fields]) OR “longitudinal studies”[All Fields] OR “prospective”[All Fields]), which yielded 63 papers published between 1986 and 2011. Continue reading
I have noted in the past couple of years a tendency of broadening the so far limited indication for adjunct systemic antibiotics for the treatment of chronic periodontitis. This is mainly due to systematic reviews with a special focused question on periodontal probing depth reduction and clinical attachment gain as outcome. New randomized controlled clinical trial have been published as well and have now discussed also an old concept, i.e. reducing the need for periodontal surgery. On the sad occasion of the demise of Walter J. Loesche I had emphasized that it was he, already in the 1980s, who had introduced this slightly provocative outcome.
My colleague Professor Eija Könönen at Turku University had asked me some time ago whether I wanted to contribute to an invited review on the microbiology of aggressive periodontitis. Not being a microbiologist (in contrast to Eija) I was a bit hesitant. But the topic was interesting and research into the matter promised to end, once and forever, persisting myths about Aggregatibacter, something which I found tempting. So, I agreed. Meanwhile, the issue had been dealt with from different perspectives, including necessarily large portions of narrative review of the literature beginning with the 1970s, and systematic searches for the role of Aggregatibacter actinomycetemcomitans and recent studies on the microbiota/microbiome of aggressive periodontitis using whole genomic DNA probes and, in particular, 16S ribosomal RNA genomic analyses. It will be published later this year in Periodontology 2000.
One of the few longitudinal studies identified by our systematic search  for a possible role of A. actinomycetemcomitans in the etiology of aggressive periodontitis was the study by Fine et al. (2007) , who
“… screened 1075 students clinically and microbiologically, and subgingival plaque, saliva and buccal epithelial-cell samples were examined for A. actinomycetemcomitans. Of those who carried the organism, 38 were followed for at least 1 year after the initial examination (test group); at the screening visit, 36 students had been diagnosed as periodontally healthy (up to one 5-mm pocket without attachment loss) or as ‘borderline’ healthy (two or more 5-mm pockets with <2 mm of attachment loss), and two were ‘potentially diseased’ (pocket depth 6 mm with attachment loss of >2 mm in one or two teeth). In addition, 58 age- and gender-matched students, confirmed negative for A. actinomycetemcomitans, formed the control group; 55 were periodontally healthy and the others were ‘borderline’ healthy at the outset of the study (see Fig. 2 in the original article). Among all 1075 students, 13 (1.2%) had already developed localized aggressive periodontitis and 13.7% were culture positive for A. actinomycetemcomitans. The majority of students were African-American or Hispanic, and the former had a slightly higher carrier rate than the latter (16.6% and 11.5%, respectively). At recall, eight students presented with bone loss, which was visible on bitewing radiographs taken yearly. All were A. actinomycetemcomitans-positive and two harbored the JP2 clone. Four had been classified at baseline as healthy, two as ‘borderline’ and two as ‘potentially diseased’. No subject in the A. actinomycetemcomitans-negative control group presented with bone loss at any recall. Survival analysis indicated a higher likelihood for carriers of A. actinomycetemcomitans to develop pockets and attachment loss over time compared with control subjects who were negative for A. actinomycetemcomitans. The authors concluded that the detection of A. actinomycetemcomitans in periodontally healthy children can serve as a risk marker for the initiation of localized aggressive periodontitis; however, given the sparseness and heterogeneity of the data (i.e. the groups seemed to differ clinically at the outset, so some carriers of A. actinomycetemcomitans might have already developed periodontitis), the evidence may be considered weak.”