The antimicrobial effect of Limosilactobacillus reuteri as probiotic on oral bacteria: A scoping review

Dysbiosis among oral microbial community in the oral cavity can lead to several oral diseases. Probiotic therapy is known to correct these imbalances. Limosilactobacillus reuteri is one of the most studied strains of probiotics and can control oral microbiota through reuterin, a wide-spectrum antimicrobial agent. The objective of this review was to evaluate the effect of the antimicrobial activity of Limosilactobacillus reuteri on the oral bacteria of humans. This review used PubMed, Scopus, EMBASE, ScienceDirect, and Google Scholar databases as bibliographic resources. Studies with matching keywords were analyzed and screened with PRISMA-ScR recommendations. Sixteen articles were selected for this review, which included a total of 832 patients. Based on this review, Limosilactobacillus reuteri has a strong antibacterial effect against Streptococcus mutans in healthy individuals but is not effective against Lactobacillus. Additionally, it has a significant antibacterial effect against Porphiromonas gingivalis in patients with periodontitis, although its effectiveness is not stable in patients with peri-implant infections. Furthermore, Limosilactobacillus reuterihas varying results against other bacteria, indicating the need for further extensive research to ensure its efficacy.


Introduction
Oral microbiome consists of a core microbiome and a variable microbiome.The core microbiome is community of predominant species that are present in various parts of the body under healthy condition.Meanwhile, a variable microbiome is a community of microorganisms species that varies and is exclusive between individuals because it has evolved in response to unique lifestyle and genotypic determinants. 13][4][5] However, over-reliance on antibiotic administration increases the risk of developing antimicrobial resistance which WHO (World Health Organization) has declared as one the global health emergencies, also known as a silent pandemic.Therefore, an alternative intervention such as probiotics gains attention to maintain oral biofilm homeostasis. 6,7obiotics are living and viable microorganisms which in adequate quantities provide benefits to the host. 8Probiotics offer many health benefits by harnessing the strengthening effects of native beneficial microflora in the body.These exogenous microorganisms, considered Generally Safe (GRAS), exhibit various beneficial properties at various levels of human health.In particular, they play an important role in protecting the host from harmful microorganisms while strengthening the immune system.Known for their ability to improve gut health, probiotics contribute to maintaining a balanced gut microbiome, which is critical for digestive function and overall well-being. 9Probiotics also improve oral flora through a bacteriotherapy mechanism by increasing the composition of harmless microflora to maintain or restore beneficial oral flora and modulating the oral microbiota to prevent pathogenic colonization. 10In addition to bacteriotherapy mechanisms, probiotics also prevent or treat oral microbiota dysbiosis through stimulation of the host's immune system and produce molecules or substances with antimicrobial effects. 8,11,12These concept provides an alternative therapy to fight infection with fewer side effects and is safer than antibiotics. 10er the past few years, probiotic therapy has been used as an adjunct treatment in clinical dentistry. 13For oral or dental purposes, probiotics need to survive in the oral ecosystem. 14In terms of oral health, Limosilactobacillus reuteri has been extensively researched and is considered one of the most studied probiotics. 15Limosilactobacillus reuteri is known for its ability to control oral microbiota through reuterin, a wide-spectrum antimicrobial agent. 16However, some studies discovered that the Limosilactobacilluss reuteri probiotic should not be recommended as an adjunct treatment for oral infection as there were no microbiota alterations between the test and control groups. 11,17,18The purpose of this study is to provide a comprehensive overview of the existing literature on the antimicrobial effect of Limosilactobacillus reuteri on oral bacteria.This review aims to synthesize and map out prior research in order to identify knowledge gaps and research needs related to this topic.By examining the breadth and depth of available literature, this review will evaluate the quality and quantity of existing research on the subject, and inform future research and practice.Ultimately, this scoping review REVISED Amendments from Version 1 Authors are pleased to present the revised version of our manuscript, which incorporates several notable enhancements based on feedback and further research.Here are the key changes made: 1.A brief explanation regarding the utilization of L. reuteri in promoting general health has been included in the discussion section.This addition provides a broader context for understanding the potential applications of L. reuteri beyond the primary focus of the study.
2. We have introduced a paragraph discussing the relationship between L. reuteri and diabetes mellitus.This addition expands the scope of the manuscript and explores an important aspect of the topic.
3. To improve the organization and clarity of the discussion section, we have subdivided it into smaller subheadings.This structural adjustment aims to facilitate easier navigation and comprehension of the presented results.4. Additional discussion has been incorporated regarding the mechanism of quorum quenching in probiotics, specifically its impact on pathogenic bacteria.Furthermore, we have provided further insights into the cytotoxic effects of Limosilactobacillus reuteri on human gingival fibroblasts.
5. Minor issues related to wording and writing have been addressed to ensure the clarity and coherence of the manuscript.
These changes collectively aim to enrich the content and readability of the manuscript, providing readers with a more comprehensive understanding of the topic.
Any further responses from the reviewers can be found at the end of the article aims to provide a foundation for future research and practice in this important area of alternative antimicrobial drug research.

Objective
This review evaluated the effect of the antimicrobial activity of Limosilactobacillus reuteri on the oral microbiota of humans.

Scoping review methods
To achieve this study's objective, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses-Extension for Scoping Reviews (PRISMA-ScR) were applied.

Research questions
What is known from the literature about the antibacterial effect of Limosilactobacillus reuteri on oral bacteria in humans?

Search methods
We ran a search for full-text manuscripts written in English in several databases, such as PubMed, Scopus, EMBASE, ScienceDirect, and Google Scholar.There were no limitations regarding the articles' publishing date at the search stage.The search was performed by identifying studies with the terms "(Lactobacillus reuteri OR Limosilactobacillus reuteri OR Probiotic) AND (Antimicrobial OR Antibacterial) AND (Oral OR Dental)".Google Scholar was included in our search strategy to ensure a comprehensive search.However, due to the large number of results obtained from Google Scholar, we limited our screening to the first 10 pages of results, which were sorted by relevance.

Selection of studies
Rayyan, developed and manufactured by Qatar Computing Research Institute in Doha, Qatar, was used as a tool for the screening and selection of studies for inclusion in this study.We imported the search results into Rayyan, de-duplicated them, and then two reviewers (NA and DFS) screened the title and abstract of each study to determine its relevance to the research question.Studies that were deemed potentially relevant by either reviewer were included for full-text review.During the full-text review stage, each reviewer independently assessed the eligibility of each study based on predetermined inclusion and exclusion criteria.Any disagreements were resolved through discussion or by involving a third reviewer (EWB).Finally, the studies that met the inclusion criteria were selected for data extraction and analysis.Rayyan was used to record the results of the screening and selection process, including the number of studies included and excluded at each stage, and to facilitate the creation of a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram.

Eligibility criteria
The inclusion criteria for the studies in this review were based on PICOS.v. Study designs: Randomized controlled trials (RCTs) and non-RCTs, case-control studies, cross-sectional, as well as prospective and retrospective cohort studies were considered for inclusion.Systematic review studies were also included to explore the studies in the review that are relevant to this study.
The exclusion criteria for this review were letters to editors, commentaries, case reports, articles with non-human samples, and non-oral/dental research articles.

Data extraction
Data were extracted from each study based on the author, year, country, study design, subject criteria, number of samples, groups in the research, strain of Limosilactobacillus reuteri used, delivery systems, other accompanying treatment, duration of intervention, bacteria affected, and the statistical analysis of oral bacteria count.

Search results
The electronic literature research process was conducted in April 2023, and 14352 studies were identified.The studies were obtained from the following four databases: PubMed, Scopus, EMBASE, ScienceDirect, and Google Scholar.A total of 1962 studies were eliminated due to duplication, 12355 studies were excluded by title and abstract screening.
From the remaining thirty-five studies, nineteen studies were also excluded due to the following reasons: their subject was not human, there was no microbiome outcome in the study, the studies in the systematic review did not met the criteria, the study was only study protocol with no result, and the probiotic used was not Limosilactobacillus reuteri or Limosilactobacillus reuteri mixed with other bacteria.Therefore, sixteen studies were selected in this review for analysis (Table 1).The PRISMA flowchart of this systematic review is presented in Figure 1.

General characteristics of included studies
Fifteen of the selected studies were randomized controlled trials (RCTs), and one study was a non-RCT experimental study.These studies were published between 2004 and 2021.Of the sixteen studies, six articles utilized healthy human subjects (four articles used healthy young adult humans, and two articles used healthy children).Three studies included in this study were conducted with peri-implant mucositis patients, two studies used peri-implantitis patients, and one study used both peri-implantitis and peri-implant mucositis patients.Additionally, one study was conducted with gingivitis patients, two studies used periodontitis patients, and one study used periodontitis patients with Diabetes Mellitus condition.A total of 832 patients were included in these studies.The duration of intervention in the included studies ranged from 10 days to 24 weeks.On the other hand, the observation periods in these studies also ranged from baseline to 26 weeks.

Strains of Limosilactobacillus reuteri Used in Studies
In two studies originating from Turkey, a combination of Limosilactobacillus reuteri ATCC 55730 and ATCC PTA 5289 strains were used, while another two studies used only the Limosilactobacillus reuteri ATCC 55730 strain.Meanwhile, one study used only the Limosilactobacillus reuteri DSM 17938 strain, and eleven other studies used a combination of Limosilactobacillus reuteri DSM 17938 and ATCC PTA 5289 strains.

Results of the quality assessment
During the quality assessment, it was found that the "low" percentage dominated the included articles, although there were still a few articles with the conclusion of "some concerns".Additionally, only one article had a "high" result, and this article was a non-RCT experimental study.Therefore, it was reasonable to have a high bias value during this assessment (as shown in Figure 2 and Table 2).As a result, we concluded that all the studies included in this review are of good quality based on the Cochrane Risk-Of-Bias (RoB 2) Tool.

Discussions
Antibiotic resistance is progressively increasing, emphasizing the urgency of finding alternative antibacterial substances. 19Many studies have tried to find alternative methods, other than antibiotics, to treat oral cavity diseases, one of which involves biofilm inhibitors, such as quorum quenching (QQ) or the inhibition of quorum sensing (QS). 20QS is a chemical signaling process of microorganisms that aims to monitor and regulate their population density.This chemical signaling system allows bacteria to coordinate their behavior and enhance their survival skills to respond to environmental changes through the growth and synthesis of biofilm matrix, enabling them to increase their resistance to conventional therapies such as antibiotics and antiseptics.Researchers and clinicians are increasingly compelled to seek novel strategies for combating biofilm-related illnesses.Among these approaches, QQ has emerged as a promising avenue.QQ targets bacterial communication networks crucial for virulence, presenting various potential applications in dentistry.Studies indicate that probiotics have the capability to inhibit QS in cariogenic and periodontopathic bacteria within the oral cavity.Through QQ, probiotics disrupt the communication pathways of these bacteria, hindering biofilm formation and virulence factor coordination. 20,21nerally, oral biofilms consist primarily of commensal species that are in equilibrium and harmless to the host.However, both local and systemic-derived insults are capable of inducing alteration towards microbial dysbiosis leading to increased number of pathogenic microbial species.The involvement of quorum sensing mechanisms in facilitating biofilm formation helps bacteria perpetuate this dysbiotic state. 20Moreover, interest in probiotics has tremendously risen over the last 10 years, and several health claims have been made regarding probiotics' antibacterial activity. 19,21In digestive studies, probiotics have a good adhesion to the gut, effectively enhancing intestinal epithelial homeostasis and interfering with the quorum sensing that favors a dysbiotic state. 22mosilactobacillus reuteri, a gut symbiont naturally found in the human intestines, has garnered significant attention for its potential health benefits.Since its isolation in 1962, numerous studies have delved into its functions and mechanisms, particularly in addressing various diseases.These include gastrointestinal disorders, hypercholesterolemia, skin infections, allergic asthma, and hand, foot, and mouth disease (HFMD), among others.Notably, research on Limosilactobacillus reuteri has increasingly focused on its role in intestinal health, with a particular emphasis on conditions like inflammatory bowel disease (IBD), colorectal cancer (CRC), and functional bowel diseases in children.The findings suggest that Limosilactobacillus reuteri offer promising prospects for enhancing overall health and well-being, particularly in the realm of digestive health and immune function. 23Furthermore, Limosilactobacillus reuteri is now widely studied for its potential benefits in oral health. 15previous study demonstrated that the combination of two strains of Limosilactobacillus reuteri, ATCC PTA 5289 and DSM 17938, did not exhibit detrimental effects on the viability of gingival fibroblasts.Employing the MTT assay, this study analyzed the viability of human gingival fibroblasts when exposed to Limosilactobacillus reuteri.These findings suggest a potential compatibility of Limosilactobacillus reuteri with gingival fibroblasts, indicating a favorable safety profile for its use in oral health applications.This current review is important as a preliminary knowledge to identify the effect of Limosilactobacillus reuteri on pathogenic bacteria in the oral cavity.24 where Limosilactobacillus reuteri was administered via yoghurt, and the count of Mutans streptococci was observed for 4 weeks.28 Five other studies observed the count of Mutans streptococci immediately after the intervention duration.[25][26][27]30 The results of these studies showed that Limosilactobacillus reuteri has an immediate and long-term effect of up to two weeks against Mutans streptococci.Related to this result, Caglar et al. (2009) conducted a study to investigate whether Limosilactobacillus reuteri ATCC 55730 survived in the oral cavity after the discontinuation of intervention.They found that Limosilactobacillus reuteri decreased gradually, where after 1 week, only 8% of bacteria were detected, and after 5 weeks, the bacteria were completely undetected.31 One limitation of the findings on Mutans streptococci presented in this scoping review is that the subjects included in the literature are all healthy individuals.While these studies provide valuable insights into the prevalence and distribution of Streptococcus mutans in healthy populations, they may not necessarily reflect the same patterns observed in individuals with other oral health disorders.In fact, other studies have shown that there are significant differences in the levels of Mutans streptococci in individuals with severe periodontitis compared to healthy individuals.32 Therefore, future research should aim to explore the distribution of Mutans streptococci in a more diverse range of populations, including those with varying levels of oral health disorders.This will help to better understand the role of Mutans streptococci in the development and progression of oral diseases and inform more targeted prevention and treatment strategies.
Four of the six previously mentioned studies also analyzed salivary lactobacilli count as a dependent variable.6][27][28] However, a study by Alamoudi et al. (2018) with healthy children as participants, discovered a positive antibacterial effect of Limosilactobacillus reuteri on salivary lactobacilli. 29This result may be influenced by the dental hygiene performed by the children using the provided fluoride toothpaste.It may also be due to the absence of salivary lactobacilli in newborns, and 40% of the 3-year-old population have it to varying degrees.Whereas salivary lactobacilli in adults depend on ecological conditions, such as pits and fissures or partially erupted wisdom teeth which provide an environment that supports its growth. 33e studies performed on healthy subjects concerning Mutans streptococci and salivary lactobacilli count were based on the prior knowledge that both microbiomes are related to dental caries.One of the salivary lactobacilli species, Lactobacillus acidophilus, has characteristics that will increase significantly 2-3 months before dental caries appear.This phenomenon is called the "explosion of Lactobacillus".However, the main oral acid production was not from lactobacilli, thereby making it only a secondary microbiome in dental caries.Lactobacillus cannot adhere to tooth surfaces on their own, as they need retention niches.On the other hand, Streptococcus mutans could produce extracellular polysaccharides to help them adhere to the tooth structure.Streptococcus mutans' main feature is its acidophilic nature.This allows it to become the dominant bacteria in the oral cavity during acidic conditions.Moreover, the intracellular polysaccharides in Streptococcus mutans create energy reserves, so the level of acid produced, especially lactic acid, remains constant even when external sugar intake is low.Hence, Mutans streptococci and salivary lactobacilli are strongly associated with dental caries. 34e impact of Limosilactobacillus reuteri on microbiomes associated with peri-implant infection All of the patients received non-surgical mechanical debridement of the peri-implant sites. 18,35,36Two of these studies found that there were no significant differences between the treated and control groups in microbiome counts after 24 weeks and 30 days of intervention with Limosilactobacillus reuteri lozenges. 18,36However, the study conducted by Laleman et al. (2020) that used probiotic drops as the drug delivery mechanism found different results compared to the other two studies.The intervention period was 12 weeks and the observation time was the baseline, week 6, week 12, and week 24.This study also evaluated the microbiome counts in the following three sites: saliva, tongue, and subgingival.
The count of Porphyromonas gingivalis was only reduced in the saliva of the treated group at the week 6 observation.The count of Aggregatibacter actinomycetemcomitans significantly decreased in the saliva and tongue at week 12.On week 24, the count of Aggregatibacter actinomycetemcomitans also decreased in the saliva.Next, the count of Prevotella intermedia in the tongue of the treated group showed a significant decrease in all of the observation periods, and a decrease was also found in the subgingival area on week 24. 35These varying results may be influenced by the drug delivery mechanisms and the sites evaluated.Nevertheless, we can conclude that the number of peri-implant microbiota evaluated at the subgingival site was generally not affected by Limosilactobacillus reuteri, whether administered by lozenge or drops.Thus, similar studies need to be conducted for the tongue area and saliva evaluation, and a larger number of samples needs to be used to obtain conclusive results.
7][38] Three of the previous four studies also analyzed Prevotella intermedia, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, and Campylobacter rectus.7][38] Similar negative results from the three studies were also noted in Prevotella intermedia, Aggregatibacter actinomycetemcomitans, and Campylobacter rectus.[38] Porphyromonas gingivalis in peri-implant mucositis patients was found to be significantly affected by Limosilactobacillus reuteri application via probiotic lozenge for thirty days.However, this result was only positive on day-90 observation time while the study also performed observation on days 30 and 60.Nevertheless, as previously described, Porphyromonas gingivalis in the saliva of peri-implantitis patients was significantly affected by Limosilactobacillus reuteri in the week-6 of observation and there was no significant difference in the week 12 and week 24 samples.However, these results were considered inconclusive due to the small number of samples and require further research. 36na et al. (2019) conducted a study with no statistically significant different results between the treated and control group in all peri-implant microbiota after administering Limosilactobacillus reuteri tablets from day 15 until day 45 of the study.However, he also analyzed the difference between the bacteria count on the day of observation and at the beginning of the study in each group, then he compared those numbers between both groups.This method resulted in significantly reduced Peptostreptococcus micros in the treated group compared to the control group, as indicated by the difference in bacterial counts between day 15 and day 45, and between day 135 and baseline.Another positive result was also found in Fusobacterium nucleatum in bacterial count on day 135 minus the bacterial count on the baseline. 38e impact of Limosilactobacillus reuteri on microbiomes associated with periodontal infection One study conducted by Iniesta et al. (2012) provided evidence that the administration of Lactobacillus reuteri DSM 17938 and PTA 5289 probiotic tablets for 28 days effectively reduced the total anaerobic bacteria counts in saliva samples after 4 weeks and Prevotella intermedia counts after 8 weeks in gingivitis patients.This probiotic combination exhibited inhibitory effects against various periodontopathogens, such as Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, Parvimonas micra, Campylobacter rectus, Capno, Eikenella corrodens, Tannerella forsythia, and Aggregatibacter actinomycetemcomitans in saliva samples.However, despite the significant total microbiological changes observed, these reductions in the target species did not translate into any clinically significant outcomes, as the inter-group differences in the clinical variables were not significant.This lack of clinical efficacy could be attributed to either the sample population or the short evaluation period.On the other hand, a significant reduction was observed only in Porphyromonas gingivalis counts in the subgingival sample from baseline to 4 weeks.These findings suggest that using Lactobacillus reuteri DSM 17938 and PTA 5289 probiotic tablets as an adjunct therapy could be promising for managing gingivitis and its associated periodontal pathogens, particularly Porphyromonas gingivalis. 39ree articles in this scoping review examined the use of Limosilactobacillus reuteri DSM 17938 as a probiotic intervention in periodontitis patients.Of these three studies, one included diabetic patients with periodontitis, while the other two used healthy individuals with no systemic disease.1][42] Interestingly, the study with diabetic patients showed a significant reduction in the number of Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola after three weeks of probiotic tablet use, which was sustained after a three-month evaluation. 40On the other hand, in line with the previous result, the study conducted by Vivekananda with a split-mouth study design in India found that only the treatment modalities that included the Limosilactobacillus reuteri tablet, either alone or in combination with scaling root planing, were able to significantly reduce the counts of pathogens tested (Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Prevotella intermedia). 41astly, the study conducted by El-bagoory et al. (2021) showed a significant reduction in the number of Porphyromonas gingivalis on the three-month and six-month evaluations after only four applications of the probiotic suspension delivered to subgingival sites, even though it was administered only at baseline, week 1, week 2, and week 4. 42 Acknowledging the potential influence of Limosilactobacillus reuteri on the results in previously mentioned diabetic samples, several studies have indicated its relationship with diabetes mellitus.While one study observed a decrease in HbA1c levels after twice-daily treatment with Limosilactobacillus reuteri DSM-17938 and ATCC PTA5289 probiotics for 3 weeks, though not statistically significant, indicating a potential trend toward improved glycemic control. 43dditionally, Limosilactobacillus reuteri strains ADR-1 and ADR-3 have shown beneficial effects on Type 2 Diabetes Mellitus, possibly mediated by changes in intestinal flora. 44Furthermore, daily treatment with Limosilactobacillus reuteri SD5865 has been associated with increased GLP-1 and GLP-2 secretion, improved insulin sensitivity, and reduced HbA1c levels, indicative of enhanced glucose metabolism. 45e effectiveness of Limosilactobacillus reuteri in treating specific periodontal pathogens in peri-implant mucositis and periodontitis patients can vary depending on the distinct microbial network shape present in these niches.Peri-implant biofilm is more homogeneous and similar to supragingival biofilm than subgingival biofilm, while subgingival biofilm in periodontitis patients contains a higher number of microorganisms.In addition to this, the host response and habitat structure surrounding implants and teeth can also affect the microbial community structure and the effectiveness of probiotics. 46Furthermore, the rough surface of dental implants increases the rate of biofilm formation around the implant, and surface roughness contributes to increased plaque buildup. 47sed on our review, it was found that Limosilactobacillus reuteri is a probiotic bacterium that exhibits varying levels of antimicrobial activity against different pathogens.However, its effectiveness can be further enhanced by combining it with other clinical care and active ingredients such as natural compounds or prebiotics.For instance, Holm et al. (2022)  showed that the antimicrobial effectiveness of Limosilactobacillus reuteri (ATCC PTA 5289) can be improved by combining it with glycerol against periodontal pathobionts and anaerobic commensals.This may be attributed to the increased production of reuterin by Limosilactobacillus reuteri from glycerol. 48Hence, combining Limosilactobacillus reuteri with other active ingredients such as natural compounds or prebiotics may be a useful strategy for improving its antimicrobial efficacy.However, further details on this strategy need to be explored, including relevant references and future research perspectives.It is worth mentioning that some newly introduced compounds have a significant influence on the oral environment.0][51] Therefore, these products should be considered in combination with Limosilactobacillus reuteri in future clinical trials.

Limitation of the study
In conducting a scoping review, it is important to consider the limitations of the study design in order to interpret the findings in a meaningful way.One limitation of the current scoping review is the potential for bias in quality assessment due to the inclusion of a non-randomized study with a high risk of bias.However, the review also included 15 other studies, all of which were randomized control trials.Of these, 9 studies were found to have a low risk of bias, while 6 studies had "some concerns" regarding risk of bias based on the Cochrane Risk-Of-Bias (RoB 2) Tool.Although the non-randomized study may have impacted the overall quality of the evidence included in the review, the findings of the randomized control trials provide important insights into the effectiveness of the interventions studied.Moreover, the inclusion of grey literature in the search strategy can help to enhance the comprehensiveness of the review.Overall, while limitations should be acknowledged and considered in the interpretation of the findings, the scoping review still provides valuable insights and can serve as a foundation for future research in the field.
Furthermore, in this scoping review, it was found that several studies included in the analysis received materials and funding from a sponsor.Additionally, one author from a study received a PhD grant from the sponsor, while another author received a lecturing fee.Nonetheless, the authors of these studies stated that the involvement of the sponsor did not have any impact on the results of their research.It is essential to acknowledge the presence of external funding sources and their potential influence on study outcomes, as transparency in reporting is crucial in scientific research.Despite the presence of sponsorship, the authors of the reviewed studies made it clear that the research conducted was not compromised, and their findings were not influenced by the sponsors.However, it is necessary to approach the results with caution, as the presence of external funding sources can still potentially affect the outcome of research studies.
information to the article.The authors may refer to this webpage for the checklist: http://www.prisma-statement.org/documents/PRISMA-ScR-Fillable-Checklist_11Sept2019.pdf Discussion Paragraph one: the authors delivered ideas about the need for alternatives to antimicrobial approaches (in this case antibiotics) by harnessing bacterial quorum sensing.At the same time, however, the authors mentioned that quorum sensing leads to antibiotic resistance.I found this conflicting and this likely confuses the reader.I would recommend the authors revisit by restructuring this part.The use of active voices is, I would suggest, preferable to strengthen the clarity of ideas delivered.For example, the first sentences could be: "Oral biofilms consist primarily of commensal species that are in equilibrium and harmless to the host.However, both oral and systemic-derived insults are capable of inducing the alteration towards microbial dysbiosis leading to an increased number of pathogenic microbial species."Minor errors: Paragraph 2: Replace "on the other side" with "moreover" Paragraph 3: Replace "conditions" with "disorders" The authors comprehensively discussed the studies included in the review.The detailed mechanisms of probiotic actions (for example, how probiotics are likely to influence bacterial quorum sensing) would provide a strong rationale for continuing the use of probiotics to regain the balance of oral microbiota.The ideas would be even more robust if the authors could expand more on the aspect such as to what extent the use of the probiotics is strongly recommended and perhaps any potential side effects should be highlighted (if no side effects are available, considering the explanation of the possible mechanism of this would be recommended).
Are the rationale for, and objectives of, the Systematic Review clearly stated?Yes

Are sufficient details of the methods and analysis provided to allow replication by others? Yes
Is the statistical analysis and its interpretation appropriate?Not applicable

Are the conclusions drawn adequately supported by the results presented in the review? Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: oral microbiology and immunology I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
The antimicrobial activity of Limosilactobacillus reuteri, one of the probiotic strains, is of great interest and brings useful information to the field of dentistry However, the following major and minor problems are observed and should be corrected before acceptance.
Major problems.
1.It would be required to describe the results of the evaluation of the effect of the antibacterial activity of Limosylactobacillus reuteri on human oral bacteria based on the 16 papers that were finally selected.
2. The discussion contains too many results and seems redundant.The discussion should be organized into important items with small headings.
3. What are the criteria for arranging the 16 papers summarized in Table 1? Wouldn't it be easier for readers to read them if they were sorted by year of publication or evidence level of study design?
Minor problems 4. The article by Badari (2020), which was selected for Systematic review, is not in the list of references.
5. The year in the text is different from the year in the list of references 5.The text is well written, but is divided into too many small paragraphs.
Are the rationale for, and objectives of, the Systematic Review clearly stated?Yes Are sufficient details of the methods and analysis provided to allow replication by others?Yes

Is the statistical analysis and its interpretation appropriate? Yes
Are the conclusions drawn adequately supported by the results presented in the review?Yes Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Oral and Maxillofacial Surgery, Reconstructive Surgery, Odontogenic Tumors I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

Firdaus Hariri
University of Malaya,, Kuala Lumpur,, Malaysia Well done to the team of researchers for this valuable review.
1) In general, the paper is well written and very structured.
2) The objective and research question are clear and the methodology used to achieve the objective is comprehensively described supplemented with the application of appropriate review protocol.
3) Results are well structured, supplemented with excellent summary tables.4) Discussion: -as Limosilactobacillus reuteri has been widely used as valuable probiotic in human, may I recommend a brief paragraph, either in 'Introduction' or at beginning of 'Discussion' on its usage in general health (authors only described its potential role in oral health).
-to supplement the discussion on paragraph 12 (on diabetic patients) with studies about the role of Limosilactobacillus reuteri in diabetes mellitus (e.g metabolic or beneficial effect).
Thank you.

Are the rationale for, and objectives of, the Systematic Review clearly stated? Yes
Are sufficient details of the methods and analysis provided to allow replication by others?Yes Is the statistical analysis and its interpretation appropriate?Not applicable

Are the conclusions drawn adequately supported by the results presented in the review? Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Metagenomic, oral health, oral and maxillofacial surgery I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.
The benefits of publishing with F1000Research: Your article is published within days, with no editorial bias • You can publish traditional articles, null/negative results, case reports, data notes and more • The peer review process is transparent and collaborative • Your article is indexed in PubMed after passing peer review • Dedicated customer support at every stage • For pre-submission enquiries, contact research@f1000.com i. Population, or participants and conditions of interest: Oral or Dental bacteria in humans ii.Interventions or exposures: Exposure to Limosilactobacilluss reuteri iii.Comparisons or control groups: a control group of microbiomes that was not exposed to Limosilactobacillus Reuteri iv.Outcomes of interest: Quantity of Oral Bacteria (Antimicrobial effect)

Figure 1 .
Figure 1.Flowchart of the scoping review.

Figure 2 .
Figure 2. The distribution of risk-of-bias judgments within each bias domain.

Table 1 .
ContinuedWe used version 2 of the Cochrane Risk-Of-Bias (RoB 2) Tool, developed and manufactured by Cochrane Collaboration, a non-profit organization based in London, United Kingdom, to assess the methodological quality of the studies.The risk of bias in each individual study was assessed by two reviewers, independently.The criteria of this assessment consisted of the following five domains: the randomisation process, deviations from intended interventions, missing outcome data, measurement of the outcome, and selection of the reported result.

Table 2 .
Quality assesment of each studies.