Quantitation of biofilm and planktonic life forms of coexisting periodontal species

Hygiene practices and antibiotic resistance among dental and medical students: a comparative study

PURPOSE

Healthcare students' hand and smartphone hygiene is critical due to potential pathogenic and antibiotic-resistant bacteria transmission. This study evaluates hygiene practices in medical and dental students at Kuwait University, exploring antibiotic resistance gene prevalence.

METHODS

Swab samples were collected from the hands and smartphones of 32 medical and 30 dental students. These samples were cultured on Columbia Blood Agar and McConkey Agar plates to quantify bacterial colony-forming units (CFUs). The extracted DNA from these colonies underwent RT-PCR to identify antibiotic resistance genes, including tem-1, shv, blaZ, and mecA. Additionally, a questionnaire addressing hygiene practices was distributed post-sample collection.

RESULTS

Medical students exhibited more frequent hand hygiene compared to dental students (P ≤ 0.0001). Although significantly fewer bacterial CFUs were found on medical students' smartphones (mean = 35 ± 53) than dental students' (mean = 89 ± 129) (P ≤ 0.05), no significant differences were observed in CFU counts on their hands (medical: mean = 17 ± 37; dental: mean = 96 ± 229). Detection of at least one of the targeted antibiotic resistance genes on medical (89% hands, 52% smartphones) and dental students' (79% hands, 63% smartphones) was not statistically significant. However, the prevalence of two genes, tem-1 and shv, was significantly higher on medical students' hands (78% and 65%, respectively) than on dental students' hands (32% and 28%, respectively).

CONCLUSION

Clinically significant prevalence of antibiotic resistance genes were found on medical and dental students' hands and smartphones, emphasizing the importance of ongoing education regarding hand hygiene and smartphone disinfection. This continuous reinforcement in the curriculum is crucial to minimizing the risk of cross-contamination.

Secretome analysis and virulence assessment in Abiotrophia defectiva

Background

Abiotrophia defectiva, although infrequently occurring, is a notable cause of culture-negative infective endocarditis with limited research on its virulence. Associated with oral infections such as dental caries, exploring its secretome may provide insights into virulence mechanisms. Our study aimed to analyze and characterize the secretome of A. defectiva strain CCUG 27639.

Methods

Secretome of A. defectiva was prepared from broth cultures and subjected to mass spectrometry and proteomics for protein identification. Inflammatory potential of the secretome was assessed by ELISA.

Results

Eighty-four proteins were identified, with diverse subcellular localizations predicted by PSORTb. Notably, 20 were cytoplasmic, 12 cytoplasmic membrane, 5 extracellular, and 9 cell wall-anchored proteins. Bioinformatics tools revealed 54 proteins secreted via the 'Sec' pathway and 8 via a non-classical pathway. Moonlighting functions were found in 23 proteins, with over 20 exhibiting potential virulence properties, including peroxiredoxin and oligopeptide ABC transporter substrate-binding protein. Gene Ontology and KEGG analyses categorized protein sequences in various pathways. STRING analysis revealed functional protein association networks. Cytokine profiling demonstrated significant proinflammatory cytokine release (IL-8, IL-1β, and CCL5) from human PBMCs.

Conclusions

Our study provides a comprehensive understanding of A. defectiva's secretome, laying the foundation for insights into its pathogenicity.

Sugar Substitute Stevia Inhibits Biofilm Formation, Exopolysaccharide Production, and Downregulates the Expression of Streptococcal Genes Involved in Exopolysaccharide Synthesis

BACKGROUND

Acid production by sucrose fermentation disturbs the balance in dental plaque by lowering the oral pH. As a consequence of the profound effect of sucrose on caries initiation and progression, many studies have been directed towards finding non-cariogenic artificial sweeteners that can be used as a substitute to sucrose. Existing literature shows that dietary sucrose upregulates the expression of biofilm associated genes involved in exopolysaccharide (EPS) production.

OBJECTIVE

In this study, we aimed to investigate the effect of the sugar substitute stevia on biofilm formation, EPS secretion, and streptococcal genes encoding glucan-binding proteins (Gbps) and glucosyltransferases (Gtfs), which are essential for the synthesis of EPS.

MATERIALS AND METHODS

Streptococcus mutans and Streptococcus gordonii were grown as biofilm cultures with or without stevia and sucrose. Biomass was quantified for biofilm and EPS production by crystal violet staining and the phenol-sulfuric acid method, respectively. Expression of gtfB and gbpB genes was studied by RT-PCR.

RESULTS

The quantities of biofilm were significantly lower when grown in the presence of stevia compared to sucrose in both species (p < 0.05). The proportion of EPS in the biofilm pellet decreased with increasing concentrations of stevia in both species but remained nearly unchanged with sucrose with respect to the control. In both streptococcal species, exposure of stevia decreased the expression of gtfB and gbpB genes compared to sucrose (p < 0.05). In comparison to the untreated control, the expression was decreased in the presence of stevia in both species, while it increased 2.5- to 4-fold in S. mutans and 1.5- to 2.5-fold in S. gordonii in the presence of sucrose.

CONCLUSION

The ability of stevia to inhibit biofilm formation, reduce EPS production, and downregulate the expression of gtfB and gbpB genes in S. mutans and S. gordonii may have potential therapeutic applications in controlling dental plaques and caries.

In vitro investigation of the impact of contemporary restorative materials on cariogenic bacteria counts and gene expression

OBJECTIVES

The aim of this study was to compare the antibacterial effect of different fluoride-containing and bioactive restorative materials, and their effect on the expression of specific biofilm-associated genes and therefore the caries process.

MATERIALS AND METHODS

The restorative materials utilized in this study included: 1. Filtek Z250, 2. Fuji II LC, 3. Beautifil II, 4. ACTIVA, and 5. Biodentine. For each material, disc-shaped specimens were prepared. The inhibitory effects against Streptococcus mutans, Lactobacillus acidophilus, and Leptotrichia shahii were tested. After incubation for 24 hours and 1 week, colony-forming units (CFUs) were enumerated. From the plates dedicated for biomass quantification and RNA purification, the target glucosyltransferase B (gtfB) and glucan-binding protein B (gbpB) genes were chosen for S. mutans. For L. acidophilus, a gene involved in exopolysaccharide synthesis (epsB) was chosen.

RESULTS

Except for Filtek Z250, all four materials showed statistically significant inhibitory effects on the biofilms of all three species. When biofilms were grown in the presence of the same four materials, the expression of S. mutans gtfB and gbpB genes, was significantly reduced. For L. acidophilus, the decrease in the expression of gtfB gene in the presence of ACTIVA was the highest change seen. The epsB gene expression also decreased. Compared to fluoride-releasing materials, bioactive materials had more inhibitory effect against L. acidophilus, both at 24 hours and 1 week.

CONCLUSIONS

Both fluoride releasing and bioactive materials exhibited a significant inhibitory effect on the biofilm growth. The expression of the targeted biofilm-associated genes was downregulated by both material groups.

CLINICAL SIGNIFICANCE

The findings from this study give insight into the antibacterial effect of fluoride-containing and bioactive materials which would help to reduce the chances for secondary caries and therefore increase the lifetime of dental restorations placed for patients.

Proteomic analysis of the periodontal pathogen Prevotella intermedia secretomes in biofilm and planktonic lifestyles

Prevotella intermedia is an important species associated with periodontitis. Despite the remarkable clinical significance, little is known about the molecular basis for its virulence. The aim of this study was to characterize the secretome of P. intermedia in biofilm and planktonic life mode. The biofilm secretome showed 109 proteins while the planktonic secretome showed 136 proteins. The biofilm and the planktonic secretomes contained 17 and 33 signal-peptide bearing proteins, 13 and 18 lipoproteins, respectively. Superoxide reductase, sensor histidine kinase, C40 family peptidase, elongation factor Tu, threonine synthase etc. were unique to biofilm. Of the ~ 30 proteins with predicted virulence potential from biofilm and planktonic secretomes, only 6 were common between the two groups, implying large differences between biofilm and planktonic modes of P. intermedia. From Gene Ontology biofilm secretome displayed a markedly higher percent proteins compared to planktonic secretome in terms of cellular amino acid metabolic process, nitrogen compound metabolic process etc. Inflammatory cytokine profile analysis revealed that only the biofilm secretome, not the planktonic one, induced important cytokines such as MIP-1α/MIP-1β, IL-1β, and IL-8. In conclusion, the revealed differences in the protein profiles of P. intermedia biofilm and planktonic secretomes may trigger further questions about molecular mechanisms how this species exerts its virulence potential in the oral cavity.

Different Scaling And Root Planing Strategies In Turkish Patients With Aggressive Periodontitis: A Randomized Controlled Clinical Trial

OBJECTIVES

The aim of this study is to compare clinical, cytokine and microbiological responses after quadrant-based scaling and root planing (Q-SRP), full-mouth SRP (FM-SRP) and full-mouth disinfection (FMD) in patients with generalized aggressive periodontitis (GAgP), which is currently termed as generalized stage III grade C periodontitis.

METHODS

Forty-two patients with GAgP were randomly assigned into groups as Q-SRP, FM-SRP or FMD with chlorhexidine. Clinical parameters were recorded and gingival crevicular fluid (GCF) and subgingival plaque samples collected at baseline, 3 and 6 months after treatment. GCF levels of interleukin (IL)-1β and IL-17 were analysed using ELISA. Quantities of six bacterial species were determined using qPCR.

RESULTS

Clinical parameters improved significantly in all groups at 3 and 6 months (p<0.05). Percentage of sites with probing depth >6 mm was lower in the FMD than Q-SRP group at 3 and 6 months (p<0.05). FMD showed significantly higher percentage of pocket closure compared to Q-SRP and FM-SRP at both 3 and 6 months after treatment (p<0.05). The IL-1β levels decreased only in the FMD group (p<0.05), whereas no changes were found in IL-17 levels in any group. The levels of five out of six bacterial species decreased at 3 and/or 6 months only in the FMD group (p<0.05).

CONCLUSIONS

The FMD treatment appears to offer superior outcome than Q-SRP and could be the first choice for patients with GAgP.

Analysis of the Effects of Food Additives on Porphyromonas gingivalis

This study aims to investigate six food additives (octanoic acid, decanoic acid, acesulfame K, aspartame, saccharin, and sucralose) used in foods for the elderly or people with dysphagia because of the effect of these food additives on Porphyromonas gingivalis (P. gingivalis), which is a keystone pathogen of periodontal diseases. The growth of P. gingivalis was inhibited by 5 mM octanoic acid, 1.25 mM decanoic acid, 1.25% acesulfame K, 0.0625% aspartame, 0.03125% saccharin, and 0.625% sucralose. In addition, these food additives showed bactericidal activity for planktonic P. gingivalis (5 mM octanoic acid, 5 mM decanoic acid, 0.25% aspartame, 0.25% saccharin, and 5% sucralose). Moreover, biofilm formation was inhibited by 10 mM octanoic acid, 10 mM decanoic acid, 10% acesulfame K, 0.35% aspartame, 0.5% saccharin, and 7.5% sucralose. Moreover, the same concentration of these food additives without aspartame killed P. gingivalis in the biofilm. Aspartame and sucralose did not show cytotoxicity to human cell lines at concentrations that affected P. gingivalis. These findings may be useful in clarifying the effects of food additives on periodontopathogenic bacteria.

In vitro evaluation of the antibacterial effect of colloidal bismuth subcitrate on Porphyromonas gingivalis and its biofilm

OBJECTIVE

To investigate the antibacterial and anti-biofilm effects of colloidal bismuth subcitrate (CBS) on Porphyromonas gingivalis (P. gingivalis) in its planktonic and biofilm forms and also compare it with that of 0.2% chlorhexidine (CHX).

DESIGN

The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of CBS were determined by the microdilution method; the bacteriostatic rate of CBS was determined by the MTT assay; the effect of CBS on the membrane integrity of P. gingivalis was investigated by the flow cytometric methods. The effects of CBS on the biomass and bacterial activity of biofilm were investigated. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were used to investigate the activity and structure of biofilms.

RESULTS

The MIC and MBC values were 18.75 µg/mL and 37.5 µg/mL. CBS could damage the cell membrane of P. gingivalis. CBS effectively inhibited biofilm formation and promoted dissociation at higher concentrations of 37.5 µg/mL and 75 µg/mL, respectively. The results also indicated an altered biofilm structure and reduced biofilm thickness and bacterial aggregation.

CONCLUSIONS

CBS affected the metabolic and physiological processes of P. gingivalis, inhibited the formation of biofilm, and disrupted the mature biofilm.

Biofilm growth and IL-8 & TNF-α-inducing properties of Candida albicans in the presence of oral gram-positive and gram-negative bacteria

Background

Interaction of C. albicans with oral bacteria is crucial for its persistence, but also plays a potential role in the infection process. In the oral cavity, it grows as part of dental plaque biofilms. Even though growth and interaction of C. albicans with certain bacterial species has been studied, little is known about its biofilm growth in vitro in the simultaneous presence of Gram-negative and Gram-positive bacteria. The aim was to evaluate the growth of C. albicans in polymicrobial biofilms comprising oral Gram-negative and Gram-positive bacteria. Further, we also aimed to assess the potential of C. albicans in the Candida-bacteria polymicrobial biofilm to elicit cytokine gene expression and cytokine production from human blood cells.

Results

C. albicans cell counts increased significantly up to 48 h in polymicrobial biofilms (p < 0.05), while the bacterial counts in the same biofilms increased only marginally as revealed by qPCR absolute quantification. However, the presence of bacteria in the biofilm did not seem to affect the growth of C. albicans. Expression of IL-8 gene was significantly (p < 0.05) higher upon stimulation from biofilm-supernatants than from biofilms in polymicrobial setting. On the contrary, TNF-α expression was significantly higher in biofilms than in supernatants but was very low (1–4 folds) in the monospecies biofilm of C. albicans. ELISA cytokine quantification data was in agreement with mRNA expression results.

Conclusion

Persistence and enhanced growth of C. albicans in polymicrobial biofilms may imply that previously reported antagonistic effect of A. actinomycetemcomitans was negated. Increased cytokine gene expression and cytokine production induced by Candida-bacteria polymicrobial biofilms and biofilm supernatants suggest that together they possibly exert an enhanced stimulatory effect on IL-8 and TNF-α production from the host.

Real-time polymerase chain reaction quantification of the salivary levels of cariogenic bacteria in patients with orthodontic fixed appliances

Aim

The aim was to investigate the salivary detection frequencies and quantities of caries‐associated bacteria from patients with orthodontic brackets.

Methods

Patients wearing orthodontic brackets (n = 40, mean age = 26 years) and healthy controls without brackets (n = 40, mean age = 17 years) were enrolled in the study. Saliva samples from each patient was collected. After DNA purification, target species comprising streptococci and a Lactobacillus species were detected and quantified from the samples using polymerase chain reaction (PCR) and real‐time quantitative PCR.

Results

Detection frequencies did not differ between the orthodontic patients and the control subjects for any target species except for Streptococcus sobrinus, which showed significantly lower detection rates in orthodontic patients (p < .05). Lactobacillus casei and Streptococcus gordonii were found at the highest detection frequencies with both species being detected in 38 (95%) of the saliva samples of orthodontic patients. Similarly, L. casei and Streptococcus salivarius were the species with highest detection frequencies (35, 87.5%) in the control subjects. Real‐time PCR revealed that Streptococcus mutans and S. salivarius quantities were significantly higher in orthodontic patients than in the control subjects (p < .05).

Conclusions

Application of orthodontic brackets for 12 months leads to increased salivary levels of cariogenic bacteria and may serve as a potential risk factor for caries initiation.

Effect of Lactobacillus rhamnosus and Bifidobacterium lactis on gingival health, dental plaque, and periodontopathogens in adolescents: a randomised placebo-controlled clinical trial

To determine the effect of a probiotic combination of Lactobacillus rhamnosus GG (LGG) and Bifidobacterium lactis BB-12 on the gingival health, dental plaque accumulation, and the oral carriage of four putative periodontal pathogens in healthy adolescents. 108 schoolboys, aged 13-15 years, participated in this study. They were divided into two groups: probiotics (n=54) and placebo (n=54). Both groups received two probiotic-laced or placebo lozenges twice a day during a four-week period. Plaque Index (PI) and Gingival Index (GI) were recorded at baseline and after four weeks. Salivary and plaque carriage of Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum were also monitored likewise. 101 subjects completed the study. A statistically significant reduction in GI was seen in the probiotic group as compared to the placebo group (P=0.012). A reduction in PI was found for both groups, with no difference observed between the groups after intervention (P=0.819). Probiotic lozenges significantly reduced levels of A. actinomycetemcomitans and F. nucleatum in saliva and plaque (P<0.05) and levels of P. gingivalis in plaque (P<0.05), while no significant changes were found in the control group. A significant reduction (P<0.001) was also noted in the total salivary bacterial counts of the test group. The short-term daily consumption of LGG and BB-12 probiotic lozenges improved the gingival health in adolescents and decreased the microbial counts of A. actinomycetemcomitans, and P. gingivalis. Hence probiotic supplements may serve as a simple adjunct to standard oral care for promoting the oral health in adolescents.

Cytokine induction of peripheral blood mononuclear cells by biofilms and biofilm supernatants of Granulicatella and Abiotrophia spp

Granulicatella and Abiotrophia species are the normal oral flora bacteria that can occasionally cause infective endocarditis. Although substantial data exists in the literature demonstrating occurrence of these species in infective endocarditis, only a few mechanistic studies on their pathogenicity are found. The aim of this study was to investigate the ability of Granulicatella and Abiotrophia species to elicit immune response from human peripheral blood mononuclear cells (PBMC). Biofilms and biofilm supernatants of Granulicatella elegans CCUG 38949, Granulicatella adiacens CCUG 27809 and Abiotrophia defectiva CCUG 27639 were used to stimulate PBMCs for 24 h. Cytokines produced were first screened using a human cytokine membrane array kit. Further, pro-inflammatory cytokines TNF-α, IL-β, and IL-17 were quantified by ELISA. The cytokine profiler array showed the induction of 15 different cytokines/chemokines including IL-1β, IL-6, IL-8, TNF-α, MCP-1, MIP-1α/MIP-1β and RANTES. ELISA quantification revealed that G. adiacens biofilm induced significantly higher (P < 0.05) levels of IL-1β, i.e., 1931 (183) pg/ml than G. elegans or A. defectiva. However, in the case of biofilm supernatants A. defectiva was the strongest, inducing 2104 (574) pg/ml. Biofilm supernatants, but not biofilms from all three species induced TNF-α only weakly. IL-17 was undetectable from any of the stimulated samples. In conclusion, Granulicatella and Abiotrophia are potent inducers of inflammatory mediators from human PBMCs. However, biofilms and biofilm supernatants from these species seem to selectively elicit stimulation of certain cytokines.

Evaluation of the biofilm formation capacity of Pasteurella multocida strains isolated from cases of fowl cholera and swine lungs and its relationship with pathogenicity

ABSTRACT: Pasteurella multocida is a Gram-negative bacillus that causes economic losses due to the development of respiratory diseases in several animal species. Among the mechanisms of virulence, the formation of biofilms is an important factor for bacterial survival in hostile environments. Studies of biofilm formation by P. multocida are needed because P. multocida is an important pathogen involved in respiratory infections. However, in contrast to other microorganisms, few studies of biofilm formation have examined P. multocida. Studies comparing the pathogenicity of microbial strains as a function of their biofilm production capacity are also rare. Consequently, the aim of this study was to evaluate the biofilm formation capacity of 94 P. multocida strains isolated from cases of fowl cholera and from swine lungs on polystyrene plates. The associations of the biofilm formation capacity with the pathogenicity index (PI) in vivo and with the presence of four genes (screened by PCR) of the tad locus (tadB, tadD, tadE and tadG), described as adhesion markers, were also determined. Strains from both animal origins were able to form biofilms. However, most of the specimens (52.13%) were classified as weak producers, and more than 40% of the strains of P. multocida (40.42%) did not produce biofilms. There was no significant difference (p>0.05) in the degree of biofilm production between the two sources of isolation. Of the analyzed strains, 56.52% contained all four genes (tadB, tadD, tadE and tadG). The PI arithmetic mean of the strains classified as non-biofilm producers was significantly different (p<0.05) from the PI of moderate-producer strains. The PI of specimens classified as weak biofilm producers also differed significantly (p<0.05) from that of the moderate-producer strains. The results indicate that even though the P. multocida strains isolated from cases of fowl cholera and swine lungs formed biofilms on polystyrene surfaces, adhesion was usually weak. The genes tadB, tadD, tadE and tadG were not significantly associated (p>0.05) with the production of biofilms and with the origin of a given strain. Finally, low virulence strains may suggest a higher biofilm formation capacity on polystyrene plates.

Do quaternary ammonium monomers induce drug resistance in cariogenic, endodontic and periodontal bacterial species?

OBJECTIVES

Antibacterial monomers were developed to combat oral biofilm acids and caries; however, little is known on whether quaternary ammonium monomers (QAMs) would induce drug resistance in oral bacteria. The objective of this study was to investigate the effects of new antimicrobial monomers dimethylaminohexadecyl methacrylate (DMAHDM) and dimethylaminododecyl methacrylate (DMADDM) on the induction of drug resistance in eight species of cariogenic, endodontic and periodontal bacteria for the first time.

METHODS

Streptococcus mutans (S. mutans), Streptococcus sanguis, Streptococcus gordonii, Enterococcus faecalis (E. faecalis), Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans), Fusobacterium nucleatum (F. nucleatum), Porphyromonas gingivalis (P. gingivalis), and Prevotella intermedia (P. intermedia) were tested. Minimum inhibitory concentration (MIC) was assessed using chlorhexidine (CHX) as control. Minimal bactericidal concentration (MBC), bacterial growth and membrane permeability properties were also investigated.

RESULTS

CHX induced drug resistance in four species. DMAHDM did not induce any resistance. DMADDM induced drug resistance in only one benign species S. gordonii. The DMADDM-resistant and CHX-resistant S. gordonii had the same MIC and MBC values as S. gordonii parental strain against DMAHDM (p>0.1), hence DMAHDM effectively inhibited the resistant strains. The resistant strains had slower growth metabolism than parental strain.

SIGNIFICANCE

DMAHDM induced no drug resistance, and DMADDM had much less drug resistance than the commonly-used CHX in the eight common oral species. With its potent antimicrobial functions shown previously, the new DMAHDM is promising for applications in restorative, preventive, periodontal and endodontic treatments to combat cariogenic and pathological bacteria with no drug resistance in all tested species.

Effect of preparation method and storage period on the stability of saliva DNA

Saliva is an attractive source for oral microbial detection and quantification since sampling is non-invasive and rapid.

OBJECTIVES

To determine whether different saliva preparation methods or preservation time periods affect DNA stability.

METHODS

Saliva samples from 4 healthy adult volunteers were processed to obtain 3 different preparations: whole saliva, and after centrifugation pellet and supernatant. Purified DNA (MasterPure™) from each sample was divided into 4 aliquots, one for immediate analysis and 3 (stored at -80°C) for later analyses after 1 week and 2 and 6 months. DNA concentrations and qPCR based quantities of Porphyromonas gingivalis, Prevotella intermedia, Parvimonas micra, Fusobacterium nucleatum, Filifactor alocis and Streptococcus mutans were determined.

RESULTS

DNA concentration did not decrease (P>0.05) during the 6-month period in any sample. Mean (SE) DNA concentrations (ng/μl) in whole saliva were 152.2 (51.2) and 147.8 (50) at day 0 and 6 months, respectively. Similarly, the values for pellet were 134.9 (42.5) and 133.6 (42.9), and for supernatant, 11 (1.9) and 8.9 (2.3), the difference being significant (P<0.001) between supernatant and whole saliva or pellet. The quantities of most bacterial species found at day 0 remained stable over the 6-month period in all saliva preparations. In supernatant, species quantities were lower (P<0.05) than in whole saliva or pellet.

CONCLUSIONS

DNA concentrations were comparable between whole saliva and pellet, suggesting that either of them can be used for DNA-based analyses. Our results also demonstrated that DNA extracted from saliva can be preserved at -80°C for at least 6 months without decrease in DNA concentration.

Experimental Models of Oral Biofilms Developed on Inert Substrates: A Review of the Literature

The oral ecosystem is a very complex environment where more than 700 different bacterial species can be found. Most of them are organized in biofilm on dental and mucosal surfaces. Studying this community is important because a rupture in stability can lead to the preeminence of pathogenic microorganisms, causing dental decay, gingivitis, or periodontitis. The multitude of species complicates biofilm analysis so its reproduction, collection, and counting are very delicate. The development of experimental models of dental biofilms was therefore essential and multiple in vitro designs have emerged, each of them especially adapted to observing biofilm formation of specific bacteria within specific environments. The aim of this review is to analyze oral biofilm models.

Interactions between Lactobacillus rhamnosus GG and oral micro-organisms in an in vitro biofilm model

Background

Probiotics have shown favourable properties in maintaining oral health. By interacting with oral microbial communities, these species could contribute to healthier microbial equilibrium. This study aimed to investigate in vitro the ability of probiotic Lactobacillus rhamnosus GG (L.GG) to integrate in oral biofilm and affect its species composition. Five oral strains, Streptococcus mutans, Streptococcus sanguinis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum and Candida albicans were involved. The group setup included 6 mono-species groups, 3 dual-species groups (L.GG + S. mutans/S. sanguinis/C. albicans), and 4 multi-species groups (4/5 species and 4/5 species + L.GG, 4 species were all the tested strains except S. mutans). Cell suspensions of six strains were pooled according to the group setup. Biofilms were grown on saliva-coated hydroxyapatite (HA) discs at 37 °C in anaerobic conditions for 64.5 h. Biofilm medium was added and refreshed at 0, 16.5, and 40.5 h. The pH of spent media was measured. Viable cells of the 16.5 h and 64.5 h biofilms were counted. 64.5 h biofilms were stained and scanned with confocal laser scanning microscopy.

Results

Our results showed that L.GG and S. mutans demonstrated stronger adhesion ability than the other strains to saliva-coated HA discs. L.GG, C. albicans, S. mutans and F. nucleatum, with poor ability to grow in mono-species biofilms demonstrated better abilities of adhesion and reproduction in dual- and/or multi-species biofilms. L.GG slightly suppressed the growth of C. albicans in all groups, markedly weakened the growth of S. sanguinis and F. nucleatum in 4sp + L.GG group, and slightly reduced the adhesion of S. mutans in L.GG+ S. mutans group.

Conclusions

To conclude, in this in vitro model L.GG successfully integrated in all oral biofilms, and reduced the counts of S. sanguinis and C. albicans and lowered the biofilm-forming ability of F. nucleatum, but only slightly reduced the adhesion of S. mutans. C. albicans significantly promoted the growth of L.GG.

Biofilm models of polymicrobial infection

Interactions between microbes are complex and play an important role in the pathogenesis of infections. These interactions can range from fierce competition for nutrients and niches to highly evolved cooperative mechanisms between different species that support their mutual growth. An increasing appreciation for these interactions, and desire to uncover the mechanisms that govern them, has resulted in a shift from monomicrobial to polymicrobial biofilm studies in different disease models. Here we provide an overview of biofilm models used to study select polymicrobial infections and highlight the impact that the interactions between microbes within these biofilms have on disease progression. Notable recent advances in the development of polymicrobial biofilm-associated infection models and challenges facing the study of polymicrobial biofilms are addressed.

Coaggregation and biofilm growth of Granulicatella spp. with Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans

BACKGROUND

Members of fastidious Granulicatella and Aggregatibacter genera belong to normal oral flora bacteria that can cause serious infections, such as infective endocarditis. Aggregatibacter actinomycetemcomitans has long been implicated in aggressive periodontitis, whereas DNA-based methods only recently showed an association between Granulicatella spp. and dental diseases. As bacterial coaggregation is a key phenomenon in the development of oral and nonoral multispecies bacterial communities it would be of interest knowing coaggregation pattern of Granulicatella species with A. actinomycetemcomitans in comparison with the multipotent coaggregator Fusobacterium nucleatum. The aim was to investigate coaggregation and biofilm formation of Granulicatella elegans and Granulicatella adiacens with A. actinomycetemcomitans and F. nucleatum strains.

RESULTS

F. nucleatum exhibited significantly (p < 0.05) higher autoaggregation than all other test species, followed by A. actinomycetemcomitans SA269 and G. elegans. A. actinomycetemcomitans CU1060 and G. adiacens did not autoaggregate. G. elegans with F. nucleatum exhibited significantly (p < 0.05) higher coaggregation than most others, but failed to grow as biofilm together or separately. With F. nucleatum as partner, A. actinomycetemcomitans strains SA269, a rough-colony wild-type strain, and CU1060, a spontaneous smooth-colony laboratory variant, and G. adiacens were the next in coaggregation efficiency. These dual species combinations also were able to grow as biofilms. While both G. elegans and G. adiacens coaggregated with A. actinomycetemcomitans strain SA269, but not with CU1060, they grew as biofilms with both A. actinomycetemcomitans strains.

CONCLUSIONS

G. elegans failed to form biofilm with F. nucleatum despite the strongest coaggregation with it. The ability of Granulicatella spp. to coaggregate and/or form biofilms with F. nucleatum and A. actinomycetemcomitans strains suggests that Granulicatella spp. have the potential to integrate into dental plaque biofilms.