Patterns of antibody response in subjects with periodontitis

Periodontal status and the efficacy of the first-line treatment of major depressive disorder

Objectives

The efficacy of treatment of major depressive disorder (MDD) is not satisfactory. Systemic inflammation may play an important role in MDD pathogenesis and treatment outcomes. Periodontal disease is the systemic inflammatory condition. Its prevalence may be as high as 45%. We aimed to assess the association of periodontal status with the outcome of 3‐month first‐line treatment of MDD with selective serotonin reuptake inhibitors.

Material and Methods

We performed the prospective cohort study during 2018/2019 at Psychiatric Hospital “Sveti Ivan,” Croatia, on a consecutive sample of 43 patients. The outcome was the MDD symptoms severity measured using the Hamilton Depression Rating Scale‐17. The periodontal status was indicated by the clinical attachment loss (CAL).

Results

Baseline periodontal status had a nonlinear significant and clinically relevant association with the MDD treatment outcome (R² change of the quadratic term = 0.12; p = 0.027). In patients with good baseline periodontal status the severity of MDD symptoms was significantly improved. When the value of CAL was ≥4.44 mm, indicating the worse periodontal status, further increase in baseline CAL was associated with the worsening of MDD treatment outcomes independently of the baseline depression severity and 14 sociodemographic and clinical predictors of treatment outcome.

Conclusions

Periodontal healthcare is accessible, and should be utilize in an integrative, multidisciplinary approach not only for the sake of psychiatric patients' quality of life and prevention of periodontal disease, but for the sake of the outcomes of psychiatric treatment as well.

Dysregulation of metallothionein and zinc aggravates periodontal diseases

BACKGROUND

Periodontitis (PD) is a multifaceted inflammatory disease connected to bacterial infection that results in the destruction of tooth supporting structures and eventually tooth loss. Given their involvement in infection and inflammation, both metallothionein (MT) and zinc (Zn) might play vital roles in the development and progression of PD. More specifically, both MT and Zn are heavily involved in regulating immune functions, controlling bacterial infection, balancing inflammatory responses, and reducing oxidative stress, all of which are associated with the pathogenesis of PD.

OBJECTIVE

This review paper will explore the physiological functions of MT and Zn and hypothesise how dysregulation could negatively affect periodontal health, leading to PD.

FINDINGS

Bacterial lipopolysaccharide (LPS) derived from periodontal pathogens, namely P. gingivalis initiates the acute phase response, thus upregulating the expression of MT which leads to the subsequent deficiency of Zn, a hallmark of periodontal disease. This deficiency leads to ineffective NETosis, increases the permeability of the gingival epithelium, and disrupts the humoral immune response, collectively contributing to PD. In addition, the presence of LPS in Zn deficient conditions favours M1 macrophage polarisation and maturation of dendritic cells, and also inhibits the anti-inflammatory activity of regulatory T cells. Collectively, these observations could theoretically give rise to the chronic inflammation seen in PD.

CONCLUSION

A disrupted MT and Zn homeostasis is expected to exert an adverse impact on periodontal health and contribute to the development and progression of PD.

Immuno-pathogenesis of Periodontal Disease: Current and Emerging Paradigms

Periodontal disease (PD) is a highly complex disease involving many factors; however, two principal facets central to initiation and progression of the majority of PD are the composition of the microbes in the sub-gingival plaque, and the host immune response to these organisms. Numerous studies point to the complexity of PD, and to the fact that despite innate and adaptive immune activation, and resultant inflammation, our immune response fails to cure disease. Stunning new findings have begun to clarify several complexities of the host-pathogen interaction of PD pointing to key roles for microbial dysboisis and immune imbalance in the pathogenesis of disease. Furthermore, these investigations have identified novel translational opportunities to intercede in PD treatment. In this review we will highlight a select few recent findings in innate and adaptive immunity, and host pathogen interactions of PD at a micro-environmental level that may have profound impact on PD progression.

Levels of serum immunoglobulin G specific to bacterial surface protein A of Tannerella forsythia are related to periodontal status

BACKGROUND

Tannerella forsythia (Tf) is a Gram-negative anaerobe implicated in the development of periodontal disease. Bacterial surface protein A (BspA) is a surface-expressed and -secreted protein that is recognized as an important virulence factor of Tf. This study was undertaken to determine whether Tf BspA induces an antibody response in periodontal disease. We hypothesized that serum immunoglobulin (Ig)G antibody levels against BspA correlate with the disease of patients.

METHODS

Sera were obtained from 100 patients with cardiac disorders and periodontal disease and 73 patients who experienced myocardial infarction but were periodontally healthy. Sera samples were assayed for anti-BspA antibody (total IgG and IgG subtypes) by enzyme-linked immunosorbent assay (ELISA). Antibody levels were measured in ELISA units by using an arbitrary patient as a standard.

RESULTS

A negative correlation was found with BspA-specific total IgG antibody titers and the severity of disease measured as the clinical attachment level (CAL) when healthy and diseased groups were analyzed separately (healthy group: [-0.23, correlation value] Student's t value [73 degrees of freedom] = 1.99; P = 0.05; diseased group: [-0.21] t [100 degrees of freedom] = 2.12; P = 0.03]). However, there was a positive correlation ([0.18 correlation value] Student's t value [173 degrees of freedom] = 2.39; P = 0.017) when healthy and diseased groups were combined. A strong positive correlation ([0.338 correlation value] Student's t value [173 degrees of freedom] = 4.69; P <0.0001) between the BspA-specific IgG titers and periodontal probing depth was observed when healthy and disease groups were combined.

CONCLUSIONS

Data demonstrated that antibodies to Tf BspA were elicited in patients with periodontal disease, and antibody levels were associated with the disease severity. Furthermore, data suggested that anti-BspA IgG might have a protective function in periodontal disease by minimizing the loss of tooth attachment tissue.

Autoimmune responses in periodontal diseases

Periodontal diseases are characterized by localized infections and inflammatory conditions and directly affect teeth supporting structures which are the major cause of tooth loss. Several studies have demonstrated the involvement of autoimmune responses in periodontal disease. Evidences of involvement of immunopathology have been reported in periodontal disease. Bacteria in the dental plaque induce antibody formation. Lymphocytes, cytokines and complement system are reported to have an important role in the progression of periodontal disease. The present review describes the involvement of autoimmune responses in periodontal diseases. The mechanisms underlying these responses are also discussed.

Determinants of serum IgG responses to periodontal bacteria in a nationally representative sample of US adults

AIM

To assess the distribution of elevated antibody titres to multiple periodontal bacteria, including established/putative pathogens and health-related species, by selected demographic, behavioural, and oral- and general health-related characteristics.

METHODS

Data from 8153 >or=40-year-old participants from the third National Health and Nutrition Examination Survey were used, including 1588 edentulous individuals. We used checkerboard immunoblotting to assess serum IgG levels to 19 periodontal species. Thresholds for elevated antibody responses were defined for each species using the 90th percentile titre in periodontal healthy participants, using two alternative definitions of periodontitis.

RESULTS

Edentulous individuals showed lower antibody responses than dentate participants, notably for titres to "red complex" species and Actinobacillus actinomycetemcomitans. Elevated titres to Porphyromonas gingivalis were twice as prevalent in participants with periodontitis than in periodontal healthy individuals. Non-Hispanic blacks and Mexican-Americans were more likely to display elevated titres for P. gingivalis compared with non-Hispanic whites (22.9%versus 19.4%versus 9.5%). Current smokers were significantly less likely to exhibit high titres to multiple bacteria than never smokers.

CONCLUSION

Demographic, behavioural, and oral- and general health-related characteristics were strong determinants of systemic antibody responses to periodontal bacteria in a nationally representative sample of US adults.

Cellular and humoral systemic and mucosal immune responses stimulated in volunteers by an oral polybacterial immunomodulator "Dentavax"

The oral polybacterial immunomodulator Dentavax (D), composed of killed cells from Klebsiella pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Candida albicans and Lactobacillus acidophilus and their lysates was created for immunoprophylaxis and therapy of oral mucosa and parodont inflammations. The stimulating effect of the preparation was evaluated in twelve volunteers immunized for 10 consecutive days. On days 7, 14, 21, 28 and 49 after the last immunization peripheral blood (PB) lymphocyte subsets, T lymphocyte activation and PB phagocytic activity, were studied by flow cytometry. PB lymphocyte proliferative responses to PHA, rIL-2, LPS and D were evaluated radiometrically. The production of TNF-alpha in supernatants of in vitro stimulated lymphocytes and specific IgA, IgM and IgG antibodies in serum and saliva was determined by ELISA. Ultrastructural morphologic changes in T and B lymphocyte populations were also investigated. Although no significant changes in the levels of basic lymphocyte subsets were detected, the early/late (CD57+/CD57-) CD8 T effectors ratio was increased at the end of the studied period, as were the percentage of PHA-responding (CD69+) T cells and PB phagocytizing cells. The most prominent lymphoprolipherative responses were measured upon costimulation with LPS+D and PHA+D on day 21. Electron-microscopic studies demonstrated a significant effect of D on both T and B cell activity. TNF-alpha concentration increased progressively from day 7 till the end of the investigation. Maximal concentrations were observed after stimulation with D and LPS. An increased level of specific salivary and serum antibodies against the components of D was found, with highest levels between days 7 and 21. Specific secretory IgA predominated in saliva as compared to IgM and IgG. Our results demonstrate the stimulating effect of Dentavax on PB lymphocyte functional activity and the specific humoral systemic and mucosal immunity.

The relationship between selected measures of periodontal status and demographic and behavioural risk factors

OBJECTIVE

To assess differences between selected periodontal measures by demographic and behavioural factors in a nationally representative sample of the United States.

METHODS

Data for 11,347 person's ages 20-79 years from the third National Health and Nutrition Examination Survey (NHANES III) were used. Indices and measures constructed from NHANES III data used for this study were: derived community periodontal index (dCPI), attachment loss extent index (ALEI), attachment loss (AL) scores, and a Periodontal Status Measure (PSM) developed for this study.

RESULTS

The influence of demographic and behavioural factors varied across the four indices examined in multivariate cumulative logistic models. Moreover, there was significant effect modification by cigarette smoking with age in the ALEI and AL models. The odds ratio (OR) of increasing periodontal disease status among 20-39 year olds as measured by AL or ALEI for current smokers compared with non-smokers were OR=6.2 (95% confidence interval (CI)=4.1, 8.7) and OR=5.6 (95% CI=3.7, 8.7), respectively. In a similar comparison, the OR for dCPI was 2.6 (95% CI=1.7, 3.8). Furthermore, Mexican American ethnicity was generally not significant in any models using dCPI, PSM, AL, or ALEI and prior dental visit was more likely to be significant only in the dCPI and PSM models.

DISCUSSION

Among the well-known demographic and behavioural influences on periodontal health status, some, such as race/ethnicity and prior dental visit status have different relationships with differing periodontal measures employed to assess periodontal status. Moreover, potential interactions among cofactors also are dependent upon the measure selected. Periodontal research findings may be influenced significantly by periodontal measure selection and its affect on measurement validity. This may have particular relevance to issues concerning disease surveillance and assessing reduction of disparities in oral health. Consequently, a renewed approach to developing appropriate measures for periodontal epidemiology is needed.

Markers of periodontal infection and preterm birth

OBJECTIVE

This study was undertaken to explore the relationship between clinical, microbiologic, and serologic markers of periodontitis and preterm birth (PTB).

STUDY DESIGN

We compared women with a singleton gestation giving birth before the 37th week (cases, n = 83) with term delivery controls (n = 120). Periodontal examination and collection of dental plaque and blood samples were performed within 48 hours after delivery. Microbial levels and maternal immunoglobulin G titers to oral bacteria were analyzed. Multivariate regression models were fitted controlling for common covariates.

RESULTS

Cases showed greater mean attachment loss (1.7 vs 1.5 mm, P = .003) and higher prevalence of periodontitis (30.1% vs 17.5%, P = .027). No differences in microbial or serum antibody levels were detected between the groups. Logistic regression revealed that PTB was associated with attachment loss (adjusted odds ratio: 2.75, 95% CI: 1.01-7.54). Linear regression indicated a significant ( P = .04) association between attachment loss and low birth weight (LBW).

CONCLUSION

The data support the notion that periodontitis is independently associated with PTB and LBW.

Longitudinal stability of serum immunoglobulin G responses to periodontal bacteria

BACKGROUND

The value of seroepidemiology in the study of periodontal infections has not been adequately explored. This study examined serum immunoglobulin (IgG) responses to periodontal bacteria in patients with periodontitis and periodontitis-free individuals over a 30-month period.

METHODS

Eighty-nine patients with chronic periodontitis and 42 control subjects with no deep periodontal pockets and no or minimal attachment loss (30-72 years old, 43% men) were included. Patients were examined at baseline, after completed periodontal therapy 4 months post-baseline, and at 30 months, and controls, at baseline and 30 months. IgG antibodies to 19 periodontal species were determined by checkerboard immunoblotting.

RESULTS

On average, patients displayed at baseline up to 800-fold higher titers than controls to all but three species. Over the 30-month period, titers remained stable at low levels in controls. In patients, periodontal conditions improved from a baseline mean probing depth of 3.6 mm, bleeding on probing of 62% and an average of 21.5 pockets of=6 mm/person, to 2.5 mm mean pocket depth, 30% bleeding on probing, and 1.2 deep pockets, at 30 months. Over time, antibody titers showed a modest decline in patients, but remained significantly elevated at 30 months in comparison with controls. Antibody-level changes over time were not significantly different between subjects that did and did not receive adjunctive systemic antibiotics.

CONCLUSIONS

Conspicuous differences in IgG titers to periodontal bacteria exist between periodontitis patients and periodontally healthy controls. Despite successful periodontal therapy, titers remained elevated over a 30-month period, suggesting that serology may mark the history of past periodontal infection.

Can presence or absence of periodontal pathogens distinguish between subjects with chronic and aggressive periodontitis? A systematic review

OBJECTIVES

The purpose of this study was to determine to what extent the presence or absence of periodontal pathogens can distinguish between subjects with chronic and aggressive periodontitis.

MATERIAL AND METHODS

A systematic review of cross sectional and longitudinal studies providing microbiological data both from patients with chronic periodontitis (ChP) and aggressive periodontitis (AgP) at a subject level. Strict inclusion criteria were applied. The presence or absence of five microorganisms was selected as primary study parameters: Actinobacillus actinomycetemcomitans (AA), Porphyromonas gingivalis (PG), Prevotella intermedia (PI), Bacteroides forsythus (BF), and Campylobacter rectus (CR).

RESULTS

The presence or absence of AA could be evaluated in 11 papers. In seven papers the presence or absence of PG could be analysed. Subject specific data on PI were available from six studies. Two studies could be used regarding the presence or absence of BF, and two regarding CR. Sensitivity and specificity of every microbiological test were individually calculated for each selected study, assuming that the clinical diagnosis of AgP or ChP was the true status the tests attempted to detect. AgP was considered to be the condition of interest and ChP was considered equivalent to 'non-AgP'. Receiver Operator Characteristic (ROC) diagrams were constructed using these data. ROC diagrams indicated the limited discriminatory ability of all of the test parameters to identify subjects with AgP. An additional assessment showed that the highly leukotoxic variant of AA was uniquely associated with patients suffering from aggressive periodontitis. However, in a high proportion of patients diagnosed with AgP the presence of this variant could not be detected.

CONCLUSION

The presence or absence of AA, PG, PI, BF or CR could not discriminate between subjects with AgP from those with ChP.

Humoral immune responses to S-layer-like proteins of Bacteroides forsythus

Bacteroides forsythus is one of the important periodontopathic bacteria, and this microorganism is known to have an S-layer outside the outer membrane. The S-layer-like antigens were recently isolated from B. forsythus, and they were found to be 270- and 230-kDa proteins in the envelope fraction. In this study, these proteins were confirmed to be specific to B. forsythus by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and they were clearly recognized by sera from patients with adult and early-onset periodontitis in Western immmunoblot analysis. We compared the immunoglobulin G (IgG) responses against the purified S-layer-like antigen by enzyme-linked immunosorbent assay. IgG responses against this antigen were low in healthy control subjects, but they were significantly higher in subjects with adult and early-onset periodontitis. Together with the fact that the IgG responses against the crude extract of B. forsythus did not rise significantly in patients with periodontitis, S-layer-like proteins are considered to be specific antigens of B. forsythus and may play an important role in the progression of periodontitis.

Serum IgG antibody response to periodontal pathogens in minority populations: relationship to periodontal disease status and progression

Differences in periodontal disease prevalence, severity, subgingival microflora and host immune response have been reported for various ethnic/racial groups, which implies that risk factors for destructive periodontal disease progression may also vary in these populations. As it is possible that these differences may be due to confounding variables other than ethnicity/race, we have measured serum IgG antibody response to six periodontal pathogens, and compared these data with microbiological, clinical and demographic parameters in three urban minority populations. The study population consisted of 23 Asiatic, 48 African-American and 37 Hispanic subjects, who were resident in the greater New York region. Clinical indices that were recorded included pocket depth, attachment level, gingival erythema, bleeding upon probing, suppuration and supragingival plaque. Attachment level measurements were taken twice at each visit, and the difference between the means of pairs of measurements taken at baseline and two months later was used to determine disease progression. Subgingival microbiological species were identified and enumerated using DNA-DNA checkerboard hybridization. Serum IgG antibody levels to Actinobacillus actinomycetemcomitans serotyopes a and b, Bacteroides forsythus, Campylobacter rectus, Porphyromonas gingivalis and Prevotella intermedia were measured by enzyme-linked immunosorbant assay (ELISA). Mean serum IgG antibody to P. gingivalis was found to be higher in the African-American group, while IgG antibody to B. forsythus was lower in the Hispanic group. However, the African-American group also had greater mean probing depth, attachment loss, number of missing teeth and numbers of individuals within the unskilled occupational group. When the data were analyzed by occupational status, mean serum IgG antibody to P. gingivalis increased from professional to skilled to unskilled groups. For the entire study population, prior disease and subsequent attachment loss were associated with elevated serum IgG antibody to P. gingivalis. Increasing pocket depth, attachment level, gingival erythema and age were also positively correlated with serum IgG antibody to P. gingivalis, but not with serum IgG antibody to the other five subgingival species. No correlation was found between whole-mouth bacterial levels and homologous serum IgG antibody levels. These results suggest that elevated serum IgG antibody to P. gingivalis reflects destructive periodontal disease status, and may be considered a risk factor for disease progression in these ethnic/racial populations. In addition, although differences in serum IgG antibody profiles to subgingival species were found among the three ethnic/racial groups, environmental and socioeconomic variables may have a greater influence on serum IgG antibody levels in these populations.

Protective effect of serum antibodies against a 110-kilodalton protein of Actinobacillus actinomycetemcomitans following periodontal therapy

Thirty-four adult patients with untreated periodontitis were randomly assigned to receive full mouth scaling alone or scaling with an adjunctive antimicrobial therapy, both followed by supportive periodontal therapy. At 24 months, specific serum immunoglobulin A (IgA), IgG and IgG subclass antibody reactivities against a 110-kDa protein of Actinobacillus actinomycetemcomitans were assessed by Western blot. In patients harboring A. actinomycetemcomitans intraorally, the IgG4 antibody reactivity against the 110-kDa protein of A. actinomycetemcomitans was associated with significantly increased survival rates of teeth and of sites not exhibiting 2 mm or more of probing attachment loss. The same trend was found for IgG3 and IgG2 antibody reactivities, but it was statistically insignificant. No association with clinical treatment outcome was observed for IgA, IgG and IgG1 antibody reactivities. The results indicated that systemic IgG4 antibody reactivity against the 110-kDa protein of A. actinomycetemcomitans may have a protective effect against periodontal disease progression in patients harboring A. actinomycetemcomitans and receiving periodontal therapy.

The pathogenesis of periodontal diseases

This informational paper was prepared by the Research, Science, and Therapy Committee of The American Academy of Periodontology, and is intended for the information of the dental profession. The purpose of the paper is to provide an overview of current knowledge relating to the pathogenesis of periodontal diseases. The paper will review biological processes thought to provide protection against periodontal infections. It will further discuss the mechanisms thought to be responsible for both overcoming and subverting such protective mechanisms and those that lead to destruction of periodontal tissues. Since an understanding of pathogenic mechanisms of disease is one foundation upon which new diagnostic and therapeutic modalities are based, the practitioner can use this information to help make decisions regarding the appropriate application of such new modalities in patient care settings.

Serum antibodies reacting with subgingival species in refractory periodontitis subjects

The purpose of this investigation was to compare the levels of serum IgG antibody to 85 subgingival species in 32 refractory periodontitis, 56 successfully treated, and 33 periodontally healthy subjects. Refractory subjects showed mean full mouth attachment loss and/or >3 sites showing attachment loss >2.5 mm within 1 year after 2 treatment modalities, scaling and root planing and surgery plus systemically administered tetracycline. Successfully-treated subjects showed mean attachment level gain and no sites with attachment loss >2.5 mm, 1 year post-therapy. Periodontally healthy subjects exhibited no pocket or attachment level >3 mm, and no evidence of progressing attachment loss during 1 year of monitoring. Baseline serum was obtained from each subject and tested against 85 subgingival species, including reference strains and strains isolated from refractory subjects, using checkerboard immunoblotting. Significance of differences in levels of serum antibody among groups were sought using the Kruskal-Wallis test. Refractory subjects constituted a heterogeneous group based on their serum antibody response to subgingival species. Some individuals had antibody reactions to many subgingival species, while other subjects showed fewer or low numbers of responses. On average, refractory subjects exhibited higher numbers and levels of serum antibody reactions to a wide range of subgingival species than successfully treated or periodontally healthy subjects. Differences in serum antibody among clinical groups were more striking at higher threshold levels of antibody (>50 microg/ml and > 100 microg/ml). The data showed that a subject was 10.1 x more likely to be refractory if the subject exhibited antibody reactions with >9 subgingival species at >50 microg/ml (p<0.001, after adjusting for multiple comparisons). Serum antibody to a subset of the test species differed among the clinical groups. Porphyromonas gingivalis, Bacteroidesforsythus, and some strains isolated from refractory subjects (a novel Neisseria sp., Enterococcus faecalis, Prevotella loescheii and Prevotella oulora) elicited high serum antibody in the successfully treated and refractory subjects. High levels of serum antibody to a Microbacterium lacticum-like organism, Streptococcus oralis, Streptococcus constellatus, Actinobacillus actinonmycetemcomitans serotype c and Haemophilus aphrophilus significantly increased the likelihood of a subject being refractory to conventional periodontal therapy.

Relationship between serum antibody levels and subgingival colonization of Porphyromonas gingivalis in patients with various types of periodontitis

Porphyromonas gingivalis is considered to be an important pathogen in periodontitis. The present study investigates the relationship between serum anti-P. gingivalis IgG antibody levels and the subgingival distribution of P. gingivalis in patients with periodontitis. We examined subgingival plaque samples from 15 patients with adult periodontitis (AP), 8 patients with early-onset periodontitis (EOP), and 6 clinically healthy individuals. The samples were collected from periodontal pockets or gingival crevices of all remaining teeth in each subject. The total number of samples was 3,024, ranging from 76 to 120 per subject. Probing depth and bleeding at each sample site were recorded. P. gingivalis was detected using a non-radioactive whole genomic DNA probe. Serum samples were taken from the subjects, and the serum anti-P. gingivalis IgG antibody titer was determined by enzyme-linked immunosorbent assay (ELISA). P. gingivalis was recovered from all AP and EOP patients, and from 3 of the 6 healthy subjects. Two significant positive correlations were observed among the subjects. The serum anti-P. gingivalis IgG antibody titer correlated with detection frequency of P. gingivalis, and the antibody titer correlated with the amount of P. gingivalis detected. Higher levels of P. gingivalis were detected in the EOP group than in the AP group. However, no significant difference was found in the serum IgG titer levels between EOP and AP patients. These findings suggest a direct relationship between the serum anti-P. gingivalis IgG levels and subgingival P. gingivalis colonization; however, the functional capabilities of IgG antibodies may vary among the various types of periodontitis patients.

On the interpretation of microbial clusters in periodontal disease

Cluster analysis is sometimes used in periodontal research to describe patterns of microbial identifications observed among cases (subjects or sites). These patterns are assumed to define subsets of cases that are meaningful, in the sense of defining periodontal subgroups that have reliable differences in some aspect of their disease. However, cluster analysis is an exploratory, first-stage technique that does not incorporate the machinery that allows one to evaluate the statistical significance and reliability of the patterns observed. Problems inherent in drawing inferences from cluster analysis are discussed and, as one methodological example of how the statistical significance of clustering might be determined, a randomization-based test for binary scaled microbial identifications is described. The introduction of cluster analysis to the study of periodontal microbiology was important and innovative, but future work needs to incorporate validation by either statistical means or independent replication. The present rarity of such confirmatory methods in the literature suggests caution in accepting specific cluster-based hypotheses about patient-microbial patterns.