Influence of Bariatric Surgery on Oral Microbiota: A Systematic Review

Abstract The study aims to systematically review the available literature to evaluate the changes in oral microbiota in patients after bariatric surgery (BS) and correlates these alterations in microorganisms with common oral manifestations. Relevant Electronic databases were systematically searched for indexed English literature. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were followed for framework designing, application, and reporting of the current systematic review. The focused PICO question was: “Is there any change in oral microbiota (O) of patients (P) who underwent BS (I) when compared with non-BS groups (C)?' Seven articles were selected for qualitative synthesis. On application of the National Institutes of Health (NIH) quality assessment tool, six studies were found to be of fair quality and one was of good quality. All the seven included studies evaluated the effect of BS on oral microbiota in humans. The outcomes of this review suggest that considerable changes take place in oral microbiota after BS which can be correlated with common oral manifestations. These changes are mainly due to the indirect effect of BS and may vary with the individuals. Due to variations in the included studies, it is difficult to proclaim any persistent pattern of oral microbiota found after BS.


Introduction
Obesity is defined as an abnormal or excessive fat accumulation that presents a risk to health. 1 As per the World Health Organization (WHO), there is an increase in obese people (body mass index [BMI] > 30 kg/m 2 ) in both developed and developing countries.When compared with the year 2000, there is a 1.5 times increase in obesity among adults (18 years and older) and more than two times increase in children (5-19 years) in 2016. 2 Thirty-nine million children under the age of 5 years were overweight or obese in 2020. 3ariatric surgery (BS) is one of the effective treatment modalities to manage morbidly obese patients and their

Selection Criteria
Inclusion and exclusion criteria are listed in ►Table 1.

Exposure and Outcome
The exposure of interest for the current study was any form of BS, irrespective of the method (type of surgery) or time (duration after the surgery).The outcome was the change in oral microbiota after BS.The focused PICO/PECO (participant, intervention/exposure, comparison, and outcome) question was: "Is there any change in oral microbiota (O) of patients (P) who underwent BS (I) when compared with non-BS groups (C)?"

Search Strategy, Study Selection, and Data Extraction
Electronic databases (PubMed/Medline, PubMed Central, Web of Science, and Cochrane library) were systematically searched by two independent reviewers (S.J. and A.A.) for articles published from 1987 to January 30, 2022.Different groups of Medical Subject Heading (MeSH) terms and supplementary non-MeSH terms were used.Details of search strings and Boolean operators are mentioned in ►Table 2. Duplicate articles were removed, and there was no discrepancy in the two lists of articles.H.A. and S.J. analyzed the titles and abstracts of all the articles based on predefined inclusion and exclusion criteria.If relevant information could not be obtained, the full text of the article was reviewed.A Manual search was conducted by searching Google, clinicaltrials.gov,and references of shortlisted articles to identify relevant articles.The selected articles were cross-checked by A.A. Full texts of shortlisted articles were reviewed by S.J. and A.A., and based on the predetermined exclusion and  Relevant data, extracted from the final articles, were tabulated in a self-designed table (►Table 3).The data extracted were as follows: first author's name, year of publication, the country where the study was conducted, study type (in vitro or in vivo), objects, the objective of the study, sample size (number of patients), gender, mean age, mean BMI of participants (before and after surgery), presence of comorbidities, oral diagnosis/findings, type of BS, microbiota investigation technique, location of specimen collection, time of specimen collection, change in levels of the microbiome, reported oral changes after BS, correlation of altered species with oral and general manifestations, and authors suggestions/conclusions.

Quality Assessment of Included Studies
The quality of included articles was assessed using the quality assessment tools of the National Heart, Lung, and Blood Institute of the National Institutes of Health (NIH) for quality assessment of the Observational Cohort and Cross-Sectional Studies and Controlled Intervention Studies. 31he criteria for assessment are as follows: Q1., "Was the research question or objective in this paper clearly stated?";Q2., "Was the study population clearly specified and defined?";Q3., "Was the participation rate of eligible persons at least 50%?"; Q4., "Were all the patients selected or recruited from the same or similar populations (including the same time period)?Were inclusion and exclusion criteria for being in the study prespecified and applied uniformly to all participants?";Q5., "Was a sample size justification, power description, or variance and effect estimates provided?";Q6., "For the analyses in this paper, were the exposure(s) of interest measured prior to the outcome(s) being measured?";Q7., "Was the timeframe sufficient so that one could reasonably expect to see an association between exposure and outcome if it existed?";"Q8: For exposures that can vary in amount or level, did the study examine different levels of the exposure as related to the outcome (e.g., categories of exposure, or exposure measured as continuous variable)?";Q9., "Were the exposure measures (independent variables) clearly defined, valid, reliable, and implemented consistently across all study participants?";Q10., "Was the exposure(s) assessed more than once over time?"; Q11., "Were the outcome measures (dependent variables) clearly defined, valid, reliable, and implemented consistently across all study participants?";Q12., "Were the outcome assessors blinded to the exposure status of participants?";Q13., "Was loss to follow-up after baseline 20% or less?"; and Q14., "Were key potential confounding variables measured and adjusted statistically for their impact on the relationship between exposure(s) and outcome(s)?"

Identification and Screening
The initial electronic database search leads to 2,030 titles (►Table 2).A total of 47 titles were found to be duplicated and were removed.Titles and abstracts of 1,983 articles were screened to exclude irrelevant articles (based on inclusion and exclusion criteria).Articles with conflicts were discussed to resolve the disagreements.Kappa score (Cohen's kappa coefficient; k ¼ 0.922) indicates a near-perfect agreement between the two reviewers.The full text of the leftover titles was assessed to choose the suitable studies, and, finally, nine articles were shortlisted.A manual search of references for these articles was performed, but no more relevant articles were found.Out of nine selected articles, one was the postoperative microbiota data 32 collected from patients where the preoperative microbiota data were published separately, 28 whereas another study was excluded because it discussed oral microbiota after BS without comparing these changes with preoperative microbiota. 33Thus finally, seven studies (reported in eight articles) were incorporated into this review.►Fig. 1 illustrates the search outcomes.

Quality Assessment of Included Studies
A total of seven studies were included in this review.The quality of one study was rated as good 13 and six studies were rated as fair 15,16,[25][26][27][28]32 with a risk of bias due to the absence of blinding. Reslts of the NIH quality assessment scale are displayed in ►Table 4.

Characteristics of Included Studies
All the included studies (n ¼ 7) evaluated the effect of BS on oral microbiota in humans.Included studies were published during the last 6 to 7 years (2015-2021; ►Table 3).Three out of seven studies were conducted in Brazil, 13,15,25 and one each was conducted in Poland, 28,32 the Czech Republic, 26 Hungary, 27 and the United States. 16Sample size researched and varied in these studies from n ¼ 27 15 to n ¼ 154. 25 The Weightloss Surgery and Oral Microflora Adawi et al.Weightloss Surgery and Oral Microflora Adawi et al.
cumulative number of female participants was higher, and they contributed to 72.9% (290) of the cumulative sample size (398), whereas male participants contributed only 27.1% (108).The mean age of participants ranged from 33.9 27 to 48 26 years, with variation in each study.Four out of seven studies reported the presence of comorbidities in the selected participants (DM, hypertension, and others) 15,16,26,28,33 ; in one study, none of the participants had comorbidities, 26 whereas two studies did not disclose these details. 13,25With regard to relevant oral findings, two studies reported the presence of periodontitis in sample groups, 13,25 two studies mentioned that there was no 16,27 ; in one study, participants were wearing removable dental prosthesis and had dental caries, 15 whereas two studies did not disclose any of these details. 26,28,32ere was a difference in the type of BS used in the selected studies.RYGB 13,15,16,25 was performed in four out of seven studies, in one study, SG was the choice of the surgical technique, 28 four different types of BS procedures were performed in one study on the selected population, 26 whereas one study did not give details about the type of weight loss surgery. 27The mean BMI of participants in included studies varied from 51.72 15 to 44.99 kg/m 225 in the pre-BS group/baseline group to 48.4 28,32 to 26.53 kg/m 225 in post-BS group.
Four out of seven studies compared the change in oral microbiota in the same selected participants before and after BS, 13,15,16,26 whereas three studies 25,27,28,32 compared this change in BS patients with those who have not undergone BS.For qualitative and quantitative analysis of the microbiota,  gingival crevicular fluid (GCF) was the source of specimen in two studies, 13,27 stimulated saliva in two, 15,16 unstimulated saliva in one, 26 and oral swabs only were collected in one study. 28,32One study collected specimens from both unstimulated saliva and the dorsum of the tongue. 25ut of the total of seven studies, three used the quantitative polymerase chain reaction (qPCR) technique for relative DNA quantification of specific microbial targets, 13,16,25 one expressed microbiological counts as colony-forming units per milliliter (CFU/mL saliva) on selective culture media, 15 one used matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) and MALDI Biotyper for identification, 27 whereas two studies used 16S rRNA gene sequence analysis technique. 26,28,32There are differences in the follow-up between the included studies.Follow-up varied from 1 day 26 to more than 24 months. 25

Results of the Individual Studies
All seven studies investigated the changes in oral microbiota after BS.These changes were reported as early as 1 day after BS 26 and continued up to 2 years of follow-up. 25The type of BS was not differentially associated with bacterial diversity or specific changes in the oral microbiota; however, each study reported a marked increase or decrease in certain species after BS.The reported trend of changes in oral microbiota was highly heterogeneous between individuals within each study.Trends in changes in oral microbiota between studies were heterogenous, primarily because only two of the studies 26,28,32 used similar approaches in identifying, and quantitating the oral microbiota.Details of changes in microbiota are described in ►Table 3.

Discussion
In the current review of literature analyses, the available studies were analyzed to evaluate the changes in oral micro-biota in patients after BS and attempted to correlate these alterations in the number and quality of microorganisms, with oral manifestations.To the best of our knowledge, to date, there is no systematic review that assesses the change in oral microbiota after BS.The findings based on the seven selected studies improve our knowledge about the changes in oral microbiota post-BS which may aid in the effective management of changes observed post-BS.The findings support that oral microbiota is altered after BS but this variation varies with the individuals.Thus the hypothesis framed can be rejected.
Oral microbiota consists of various microbial species which colonizes in different areas of the oral cavity.The characteristics of each area determine the configuration of microbiota. 34There is a critical balance between these microorganisms and the host.In the presence of systemic diseases and /or if oral hygiene is not adequately maintained, this equilibrium gets disturbed, and the quality and quantity of microbiota get altered which may manifest as oral diseases like periodontitis, caries, gingivitis, oral mucosal changes, and others.][40] Obesity is a complex state which involves excessive fat accumulation that can have a negative effect on the overall health of an individual.Vgontzas et al 41 reported that proinflammatory cytokines, which are secreted by fat tissues, are directly proportional to BMI and visceral obesity.This systemic inflammation alters the oral microbiota in obese individuals, which are found to have higher levels of phylum bacteroidetes (T.forsythia and P. gingivalis), 42,43 phylum spirochaetes (T.denticola), 43 phylum firmicutes (Granulicatella adiacens and Streptococcus oligofermentans), phylum actinobacteria (actinomyces), phylum proteobacteria (Aggregatibacter) as compared with nonobese individuals. 44In addition to this, comorbidities associated with obesity like type-2 DM, hypertension, hyperlipidemia, and others, also alter the oral microbiota. 16,45BS is an effective treatment modality to manage morbidly obese patients and their related comorbidities in the long term. 4Studies have reported a change in oral microbiota 13,15,16,[25][26][27][28]32 in patients who have undergone BS procedures. Thee alterations can be associated with the site of the oral cavity.One of the prerequisites regarding microbiota analysis and comparison between groups is the absence of any relevant disease before intervention, so that observed alteration can be attributed to intervention.46 In the current review, three studies reported the presence of oral disease preoperatively 13,15,25 and two studies did not disclose any of these details, 26,28,32 Five out of seven studies included antibiotic administration in exclusion criteria.One study did not include it.26 In another study, 16 the exclusion criteria was those patients who have received antibiotics within the previous 6 months, but during methodology, the authors mentioned administering a single dose of antibiotics to patients.Studies reported that the use of antibiotics can alter the composition of oral microflora 47,48 which can return back to normal after 14 days of antibiotic administration.49 When changes in salivary microbiota after BS were considered, Hashizume et al 15 reported an increase in Streptococcus mutans and Candida albicans and a decrease in Lactobacillus spp.This Increase in C. albicans in their study can be related to the inclusion of patients with comorbidities wearing removable dentures.Pataro et al 25 reported higher oral and lower stomach bacteria frequency in the BS group.They reported a nonsignificant decrease in H. pylori and an increase in the frequency of red complex species (P. gigivalis, T. forsythia, and T. denticola) in the bariatric group with a much higher number in patients having periodontitis before BS.Their results were in accordance with Jaiswal et al, 50 who reported no improvement in pocket depth and clinical attachment level after 6 months of BS.Džunková et al 26 reported a significant increase in V. atypica and a significant decrease in P. pasteri.They concluded that GI microbiota is affected directly by BS, whereas salivary microbiota is altered indirectly. Shillito et al 16 reported a 10-fold increase in Bifidobacteria species. They reprted simultaneous changes in oral and lower GI microbiota which could be due to the correction of the systemic mucosal immune defect after BS and the direct influence of oral microbiota which is continuously swallowed.51 Concerning changes in GCF microbiota, Sales-Peres et al 13 reported a significant increase in P. gingivalis and T. forsythia and a significant decrease in T. denticola and P. intermedia. Thy reported worsened periodontal conditions 6 months after BS and slight improvement after 12 months of followup. Depite reduction in the body's inflammatory response, increased periodontal destruction was related to being due to indirect damage mediated by the immunoinflammatory response.They proposed that these changes could be due to frequent eating, osteoporosis, 52 and nutritional deficiencies which are common after BS.Balogh et al 27 reported a marked increase in germ count of streptococcus, albicans, and nonalbicans Candida and a significant decrease in Granulicatella, Actinomyces, and Fusobacterium.An increase in the proportion of patients affected by Prevotella sp. was also reported.The non-albicans species (C.dubliniensis, C. kefyr, and C. lusitaniae) found were similar to those isolated from the oral cavity of immunosuppressed patients.They concluded that despite changes in oral microbiota after BS, patients are unlikely to develop periodontitis if they have uninflamed periodontal conditions and good oral hygiene maintenance preoperatively.
Concerning changes in oral scrapings microbiota, Stefura et al 28,32 reported more proteobacteria species preoperatively, in the patients who have positive weight loss outcome (% expected weight loss [EWL] >50%), when compared with the patients who have negative weight loss outcome (% EWL < 50%), in which actinobacteria species is higher preoperatively.They reported an increase in bacteroidetes, proteobacteria, and actinobacteria species postoperatively.Type of BS and patient's age were important factors in determining the amount of weight loss.
All the included studies had indicated a change in quality and quality of oral microbiota after BS but had dissimilar results when type and number of species were considered.Most of the studies had a common consensus that these changes in oral microbiota are not directly related to BS but could be due to indirect reasons.These reasons could be increased frequency of meals (sucrose), 13,15,26 underreporting of food intake by patient, 33 change in food consistency, 15 change in nutritional composition of food, 33 nutritional deficiencies, 13 altered oral pH due to frequent episodes of gastrooesophageal reflux, 26 use of proton pump inhibitors, 53 change in gut-brain axis regulation, 26 alterations in taste perception, 26,54 presence of systemic diseases/comorbidities/immunological factors, 15 presence of dentures in mouth, 15 oral health status before BS, 27 dental hygiene maintenance, 27 and individual-specific resident bacteria. 26hese changes in oral microbiota can be correlated with oral and general manifestations to some extent.Altered species which have been reported to have a positive correlation with periodontitis include P. gingivalis, T. forsythia, T. denticola, P. intermedia, phyla bacteroidetes, Prevotella salivae, A. actinomycetemcomitans, P. micra, and C. rectus 25,[55][56][57][58][59][60][61] .Whereas Neisseria and Bifidobacteria have a negative correlation with periodontitis. 62,63S. Mutans, phylum actinobacteria, and V. atypica have a positive correlation with dental caries. 64Whereas, Megasphaera micronuciformis and C. albicans, to some extent, have a negative correlation with caries. 64,65C. albicans and nonalbicans Candida species have a positive correlation with immunosuppression, [66][67][68] H. pylori and phyla proteobacteria 67 have a positive correlation with gastritis, and P. gingivalis has been positively related to cardiovascular diseases. 66,67nowledge of changes in oral microbiota and their relation to GI microbiota is very important.The oral cavity can act as an extra gastric pool for many microorganisms.0][71][72][73][74] Studies have reported three pathways for oral-gut allocation of microbiota 75,76 as follows: (1) direct invasion of the intestinal tract through the esophagus by oral microbiota; (2) through the blood cycling route, pathogenic oral microorganisms, which cause periodontitis, can enter the systemic circulation through the periodontal blood and may act on the whole body, and (3) low-grade inflammatory state caused by the metabolites of oral microbiota that enter the bloodstream and the systemic circulation.Also, it is easier/convenient to obtain oral specimens as compared with faecal specimens in long-term follow-up cases to evaluate the changes in the microbiota.
A dentist can play a vital role in monitoring the oral cavity of patients before and during follow-up visits after BS.It is evitable that at all stages, good oral health should be maintained for these patients to improve their chewing efficiency to keep pathogenic species under control and to reduce systemic complications due to bacteremia.Further long-European Journal of Dentistry Vol. 17 No.3/2023 © 2022.The Author(s).
Weightloss Surgery and Oral Microflora Adawi et al. 611 term studies focusing on monitoring oral microfloral changes and identifying optimal oral microfloral composition after BS may help in better management of these patients.
The outcomes from the current study are also dependent on the different duration of follow-up and different approaches used by the selected articles.The follow-up period varied from 1 day 26 to 2 years, 25 and the location of oral specimen collection was also varied.27][28]32 Thus generalization of outcomes was difficult.Also, there was no consistency in the study groups.Due to these limitations, meta-analysis was not feasible.The detailed study selection approach followed is the key point of this review.All studies related to BS and changes in oral microbiota were analyzed, thus making sure that no relevant study is missed.

Conclusion
The outcomes of this systematic review indicate that considerable changes take place in oral microbiota after BS which can be correlated with common oral manifestations.These changes are mainly due to the indirect effect of BS and may vary with the individuals.Due to variations in the included studies, it is difficult to proclaim any persistent pattern of oral microbiota found after BS.Further long-term investigations are required to get a better picture of the altered microbiota.

Fig. 1
Fig. 1 Flowchart of article inclusion strategy based on PRISMA guidelines.PRISMA, the Preferred Reporting Items for Systematic Reviews and Meta-analyses.

Table 1
Inclusion and exclusion criteria

Table 3
Main characteristics of the studies included European Journal of Dentistry Vol. 17 No.3/2023 © 2022.The Author(s).

Table 3 (
Continued)Weightloss Surgery and Oral Microflora Adawi et al. 607 a. Statistically significant increase: P. gingivalis and T. forsythia b.Statistically non-significant increase: T. denticola and P. intermedia c.Statistically significant or non-significant decrease: none 2. Changes after 12 months of surgery (in comparison to 6 months) a. Statistically significant decrease: P. gingivalis b.Statistically nonsignificant decrease: T. forsythia, T. denticola & P. intermedia c.Statistically significant or nonsignificant increase: 3. Changes after 12 months of surgery (in comparison to Pre BS) a. Increase: P. gingivalis, T. forsythia b.Decrease: P. intermedia, T. denticola • Increase in the severity of periodontal disease (increase in pocket depth, increased loss of clinical attachment, increase in bleeding index) • P. gingivalis, T. forsythia, T. denticola and P. intermedia: þve correlation with periodontal disease • P. gingivalis: European Journal of Dentistry Vol. 17 No.3/2023 © 2022.The Author(s).

Table 4
Quality analysis outcomes of the included studies (NIH quality assessment tool) Abbreviations: N, no; NA, not applicable; NIH, National Institutes of Health; NR, not reported; Y, yes. a Will not count negatively towards the quality rating.