Codon-optimized fluorescent mTFP and mCherry for microscopic visualization and genetic counterselection of streptococci and enterococci

Intraspecies interactions of Streptococcus mutans impact biofilm architecture and virulence determinants in childhood dental caries

Early childhood dental caries (ECC) is the most common chronic disease among children, especially among low socioeconomic populations. Streptococcus mutans is most frequently associated with initiation of ECC. Although many studies report children with multiple S. mutans strains (i.e., genotypes) have greater odds of developing ECC, studies investigating intraspecies interactions in dental caries are lacking. This study investigates the impact of intraspecies interactions on cariogenic and fitness traits of clinical S. mutans isolates using in vitro and in vivo approaches. Association analysis evaluated if presence of multiple S. mutans genotypes within the first year of colonization was associated with caries. Initially, clinical S. mutans isolates from 10 children were evaluated. S. mutans strains (G09 and G18, most prevalent) isolated from one child were used for subsequent analysis. Biofilm analysis was performed for single and mixed cultures to assess cariogenic traits, including biofilm biomass, intra-polysaccharide, pH, and glucan. Confocal laser scanning microscopy (CLSM) and time-lapse imaging were used to evaluate spatial and temporal biofilm dynamics, respectively. A Drosophila model was used to assess colonization in vivo. Results showed the mean biofilm pH was significantly lower in co-cultured biofilms versus monoculture. Doubling of S. mutans biofilms was observed by CLSM and in vivo colonization in Drosophila for co-cultured S. mutans. Individual strains occupied specific domains in co-culture and G09 contributed most to increased co-culture biofilm thickness and colonization in Drosophila. Biofilm formation and acid production displayed distinct signatures in time-lapsed experiments. This study illuminates that intraspecies interactions of S. mutans significantly impacts biofilm acidity, architecture, and colonization.IMPORTANCEThis study sheds light on the complex dynamics of a key contributor to early childhood dental caries (ECC) by exploring intraspecies interactions of different S. mutans strains and their impact on cariogenic traits. Utilizing clinical isolates from children with ECC, the research highlights significant differences in biofilm architecture and acid production in mixed versus single genotype cultures. The findings reveal that co-cultured S. mutans strains exhibit increased cell density and acidity, with individual strains occupying distinct domains. These insights, enhanced by use of time-lapsed confocal laser scanning microscopy and a Drosophila model, offer a deeper understanding of ECC pathogenesis and potential avenues for targeted interventions.

A novel infective endocarditis virulence factor related to multiple functions for bacterial survival in blood was discovered in Streptococcus sanguinis

We identified the role of a conserved hypothetical protein (SSA_0451) in S. sanguinis that is involved in the virulence of infective endocarditis. An in vitro whole blood killing assay and rabbit endocarditis model studies revealed that the SSA_0451 mutant (ΔSSA_0451) was significantly less virulent than the wild-type (SK36) and its complementation mutant (ΔSSA_0451C). The mechanism underlying the SSA_0451 mutant's reduced virulence in infective endocarditis was evidentially linked to oxidative stress and environmental stress. The genes related to the survival of S. sanguinis in an oxidative stress environment were downregulated in ΔSSA_0451, which affected its survival in blood. Our findings suggest that SSA_0451 is a novel IE virulence factor and a new target for drug discovery against IE.

Time-lapse confocal microscopy to study in vitro Streptococcus mutans surface colonization

The cariogenicity of Streptococcus mutans relates to its ability to form biofilms on dental surfaces. The aim of this work was to develop a flowcell system compatible with time-lapse confocal microscopy to compare the adhesion and accumulation of S. mutans cells on surfaces in unsupplemented media against media containing sucrose or sucralose (a non-metabolized sweetener) over a short period of time. Fluorescent S. mutans 3209/pVMCherry was suspended in unsupplemented media or media supplemented with 1% sucrose or 1% sucralose and passed through a 3D-printed flowcell system. Flowcells were imaged over 60 minutes using a confocal microscope. Image analysis was performed, including a newly developed object-movement-based method to measure biomass adhesion. Streptococcus mutans 3209/pVMCherry grown in 1% sucrose-supplemented media formed small, dense, relatively immobile clumps in the flowcell system measured by biovolume, surface area, and median object centroid movement. Sucralose-supplemented and un-supplemented media yielded large, loose, mobile aggregates. Architectural metrics and per-object movement were significantly different (P < 0.05) when comparing sucrose-supplemented media to either unsupplemented or sucralose-supplemented media. These results demonstrate the utility of a flowcell system compatible with time-lapse confocal microscopy and image analysis when studying initial biofilm formation and adhesion under different nutritional conditions.

Intraspecies interactions of Streptococcus mutans impact biofilm architecture and virulence determinants in childhood dental caries

Early childhood dental caries (ECC) is the most common chronic disease among children with a heavy disease burden among low socioeconomic populations. Streptococcus mutans is most frequently associated with initiation of ECC. Many studies report children with multiple S. mutans strains (i.e., genotypes) having greater odds of developing ECC, studies investigating intraspecies interactions in dental caries are lacking. In this study, the impact of intraspecies interactions on cariogenic and fitness traits of clinical S. mutans isolates are investigated using in-vitro and in-vivo approaches. Initially clinical S. mutans isolates of 10 children from a longitudinal epidemiological study were evaluated. S. mutans strains (G09 and G18, most prevalent) isolated from one child were used for subsequent analysis. Association analysis was used to determine if presence of multiple S. mutans genotypes within the first-year of colonization was associated with caries. Biofilm analysis was performed for single and mixed cultures to assess cariogenic traits, including biofilm biomass, intra-polysaccharide, pH, and glucan. Confocal Laser Scanning Microscopy (CLSM) and time-lapse imaging were used to evaluate spatial and temporal biofilm dynamics, respectively. A Drosophila model was used to assess colonization in-vivo. Mean biofilm pH was significantly lower in co-cultured biofilms as compared with monoculture biofilms. Doubling of S. mutans in-vitro biofilms was observed by CLSM and in-vivo colonization in Drosophila for co-cultured S. mutans. Individual strains occupied specific domains in co-culture and G09 contributed most to increased co-culture biofilm thickness and colonization in Drosophila. Biofilm formation and acid production displayed distinct signatures in time-lapsed experiments.

Illuminating the oral microbiome and its host interactions: tools and approaches for molecular microbiology studies

Advancements in DNA sequencing technologies within the last decade have stimulated an unprecedented interest in the human microbiome, largely due the broad diversity of human diseases found to correlate with microbiome dysbiosis. As a direct consequence of these studies, a vast number of understudied and uncharacterized microbes have been identified as potential drivers of mucosal health and disease. The looming challenge in the field is to transition these observations into defined molecular mechanistic studies of symbiosis and dysbiosis. In order to meet this challenge, many of these newly identified microbes will need to be adapted for use in experimental models. Consequently, this review presents a comprehensive overview of the molecular microbiology tools and techniques that have played crucial roles in genetic studies of the bacteria found within the human oral microbiota. Here, we will use specific examples from the oral microbiome literature to illustrate the biology supporting these techniques, why they are needed in the field, and how such technologies have been implemented. It is hoped that this information can serve as a useful reference guide to help catalyze molecular microbiology studies of the many new understudied and uncharacterized species identified at different mucosal sites in the body.

Spatiotemporal monitoring of a periodontal multispecies biofilm model: demonstration of prebiotic treatment responses

Biofilms are complex polymicrobial communities which are often associated with human infections such as the oral disease periodontitis. Studying these complex communities under controlled conditions requires in vitro biofilm model systems that mimic the natural environment as close as possible. This study established a multispecies periodontal model in the drip flow biofilm reactor in order to mimic the continuous flow of nutrients at the air-liquid interface in the oral cavity. The design is engineered to enable real-time characterization. A community of five bacteria, Streptococcus gordonii-GFPmut3*, Streptococcus oralis-GFPmut3*, Streptococcus sanguinis-pVMCherry, Fusobacterium nucleatum, and Porphyromonas gingivalis-SNAP26 is visualized using two distinct fluorescent proteins and the SNAP-tag. The biofilm in the reactor develops into a heterogeneous, spatially uniform, dense, and metabolically active biofilm with relative cell abundances similar to those in a healthy individual. Metabolic activity, structural features, and bacterial composition of the biofilm remain stable from 3 to 6 days. As a proof of concept for our periodontal model, the 3 days developed biofilm is exposed to a prebiotic treatment with L-arginine. Multifaceted effects of L-arginine on the oral biofilm were validated by this model setup. L-arginine showed to inhibit growth and incorporation of the pathogenic species and to reduce biofilm thickness and volume. Additionally, L-arginine is metabolized by Streptococcus gordonii-GFPmut3* and Streptococcus sanguinis-pVMCherry, producing high levels of ornithine and ammonium in the biofilm. In conclusion, our drip flow reactor setup is promising in studying spatiotemporal behavior of a multispecies periodontal community.ImportancePeriodontitis is a multifactorial chronic inflammatory disease in the oral cavity associated with the accumulation of microorganisms in a biofilm. Not the presence of the biofilm as such, but changes in the microbiota (i.e., dysbiosis) drive the development of periodontitis, resulting in the destruction of tooth-supporting tissues. In this respect, novel treatment approaches focus on maintaining the health-associated homeostasis of the resident oral microbiota. To get insight in dynamic biofilm responses, our research presents the establishment of a periodontal biofilm model including Streptococcus gordonii, Streptococcus oralis, Streptococcus sanguinis, Fusobacterium nucleatum, and Porphyromonas gingivalis. The added value of the model setup is the combination of simulating continuously changing natural mouth conditions with spatiotemporal biofilm profiling using non-destructive characterization tools. These applications are limited for periodontal biofilm research and would contribute in understanding treatment mechanisms, short- or long-term exposure effects, the adaptation potential of the biofilm and thus treatment strategies.

Corrected and Republished from: "Understanding Lactobacillus paracasei and Streptococcus oralis Biofilm Interactions through Agent-Based Modeling"

As common commensals residing on mucosal tissues, Lactobacillus species are known to promote health, while some Streptococcus species act to enhance the pathogenicity of other organisms in those environments. In this study we used a combination of in vitro imaging of live biofilms and computational modeling to explore biofilm interactions between Streptococcus oralis, an accessory pathogen in oral candidiasis, and Lactobacillus paracasei, an organism with known probiotic properties. A computational agent-based model was created where the two species interact only by competing for space, oxygen, and glucose. Quantification of bacterial growth in live biofilms indicated that S. oralis biomass and cell numbers were much lower than predicted by the model. Two subsequent models were then created to examine more complex interactions between these species, one where L. paracasei secretes a surfactant and another where L. paracasei secretes an inhibitor of S. oralis growth. We observed that the growth of S. oralis could be affected by both mechanisms. Further biofilm experiments support the hypothesis that L. paracasei may secrete an inhibitor of S. oralis growth, although they do not exclude that a surfactant could also be involved. This contribution shows how agent-based modeling and experiments can be used in synergy to address multiple-species biofilm interactions, with important roles in mucosal health and disease. IMPORTANCE We previously discovered a role of the oral commensal Streptococcus oralis as an accessory pathogen. S. oralis increases the virulence of Candida albicans infections in murine oral candidiasis and epithelial cell models through mechanisms which promote the formation of tissue-damaging biofilms. Lactobacillus species have known inhibitory effects on biofilm formation of many microbes, including Streptococcus species. Agent-based modeling has great advantages as a means of exploring multifaceted relationships between organisms in complex environments such as biofilms. Here, we used an iterative collaborative process between experimentation and modeling to reveal aspects of the mostly unexplored relationship between S. oralis and L. paracasei in biofilm growth. The inhibitory nature of L. paracasei on S. oralis in biofilms may be exploited as a means of preventing or alleviating mucosal fungal infections.

Understanding Lactobacillus paracasei and Streptococcus oralis Biofilm Interactions through Agent-Based Modeling

As common commensals residing on mucosal tissues, Lactobacillus species are known to promote health, while some Streptococcus species act to enhance the pathogenicity of other organisms in those environments. In this study, we used a combination of in vitro imaging of live biofilms and computational modeling to explore biofilm interactions between Streptococcus oralis, an accessory pathogen in oral candidiasis, and Lactobacillus paracasei, an organism with known probiotic properties. A computational agent-based model was created where the two species interact only by competing for space, oxygen and glucose. Quantification of bacterial growth in live biofilms indicated that S. oralis biomass and cell numbers were much lower than predicted by the model. Two subsequent models were then created to examine more complex interactions between these species, one where L. paracasei secretes a surfactant, and another where L. paracasei secretes an inhibitor of S. oralis growth. We observed that the growth of S. oralis could be affected by both mechanisms. Further biofilm experiments support the hypothesis that L. paracasei may secrete an inhibitor of S. oralis growth, although they do not exclude that a surfactant could also be involved. This contribution shows how agent-based modeling and experiments can be used in synergy to address multiple species biofilm interactions, with important roles in mucosal health and disease. IMPORTANCE We previously discovered a role of the oral commensal Streptococcus oralis as an accessory pathogen. S. oralis increases the virulence of Candida albicans infections in murine oral candidiasis and epithelial cell models through mechanisms which promote the formation of tissue-damaging biofilms. Lactobacillus species have known inhibitory effects on biofilm formation of many microbes, including Streptococcus species. Agent-based modeling has great advantages as a means of exploring multifaceted relationships between organisms in complex environments such as biofilms. Here, we used an iterative collaborative process between experimentation and modeling to reveal aspects of the mostly unexplored relationship between S. oralis and L. paracasei in biofilm growth. The inhibitory nature of L. paracasei on S. oralis in biofilms may be exploited as a means of preventing or alleviating mucosal fungal infections.

Manganese transport by Streptococcus sanguinis in acidic conditions and its impact on growth in vitro and in vivo

Streptococcus sanguinis is an oral commensal and an etiological agent of infective endocarditis. Previous studies have identified the SsaACB manganese transporter as essential for endocarditis virulence; however, the significance of SsaACB in the oral environment has never been examined. Here we report that a ΔssaACB deletion mutant of strain SK36 exhibits reduced growth and manganese uptake under acidic conditions. Further studies revealed that these deficits resulted from the decreased activity of TmpA, shown in the accompanying paper to function as a ZIP‐family manganese transporter. Transcriptomic analysis of fermentor‐grown cultures of SK36 WT and ΔssaACB strains identified pH‐dependent changes related to carbon catabolite repression in both strains, though their magnitude was generally greater in the mutant. In strain VMC66, which possesses a MntH transporter, loss of SsaACB did not significantly alter growth or cellular manganese levels under the same conditions. Interestingly, there were only modest differences between SK36 and its ΔssaACB mutant in competition with Streptococcus mutans in vitro and in a murine oral colonization model. Our results suggest that the heterogeneity of the oral environment may provide a rationale for the variety of manganese transporters found in S. sanguinis.

Identification of Streptococcus mutans genes involved in fluoride resistance by screening of a transposon mutant library

Fluoride has been used as an effective anticaries agent for more than 70 years, which might result in the emergence of fluoride-resistant strains. However, the fluoride resistance mechanism and the cariogenic properties of fluoride-resistant mutant for cariogenic bacterial species Streptococcus mutans remain largely unknown. We describe here the construction and characterization of a mariner-based transposon system designed to be used in S. mutans, which is also potentially applicable to other streptococci. To identify genetic determinants of fluoride resistance in S. mutans, we constructed a library of S. mutans transposon insertion mutants and screened this library to identify mutants exhibiting fluoride resistance phenotype. Two mutants were found to carry transposon insertion in two different genetic loci (smu.396 and smu.1291c), respectively. Our subsequent genetic study indicates the fluoride-resistant phenotype for the mutant with the insertion in smu.1291c is resulting from the constitutive overexpression of downstream operon smu.1290c-89c, which is consistent with the previous reports. We also demonstrate for the first time that the deletion of smu.396 is responsible for the fluoride-resistant phenotype and that the combining of smu1290c-89c overexpression and smu.396 deletion in one strain could attribute an additive effect on the fluoride resistance. In addition, our results suggest that the biological fitness of those fluoride-resistant mutants is reduced compared to that of wild-type strain. Overall, our identification and characterization of genetic determinants responsible for fluoride resistance in S. mutans expand our understanding of the fluoride resistance mechanism and the biological consequence of the fluoride resistance strains.

Involvement of Chromosomally Encoded Homologs of the RRNPP Protein Family in Enterococcus faecalis Biofilm Formation and Urinary Tract Infection Pathogenesis

Enterococcus faecalis is an opportunistic pathogen capable of causing infections, including endocarditis and urinary tract infections (UTI). One of the well-characterized quorum-sensing pathways in E. faecalis involves coordination of the conjugal transfer of pheromone-responsive plasmids by PrgX, a member of the RRNPP protein family. Members of this protein family in various Firmicutes have also been shown to contribute to numerous cellular processes, including sporulation, competence, conjugation, nutrient sensing, biofilm formation, and virulence. As PrgX is a plasmid-encoded RRNPP family member, we surveyed the genome of the multidrug-resistant strain V583 for additional RRNPP homologs using computational searches and refined those identified hits for predicted structural similarities to known RRNPP family members. This led us to investigate the contribution of the chromosomally encoded RRNPP homologs to biofilm processes and pathogenesis in a catheter-associated urinary tract infection (CAUTI) model. In this study, we identified five such homologs and report that 3 of the 5 homologs, EF0073, EF1599, and EF1316, affect biofilm formation as well as outcomes in the CAUTI model.IMPORTANCE Enterococcus faecalis causes health care-associated infections and displays resistance to a variety of broad-spectrum antibiotics by acquisition of resistance traits as well as the ability to form biofilms. Even though a growing number of factors related to biofilm formation have been identified, mechanisms that contribute to biofilm formation are still largely unknown. Members of the RRNPP protein family regulate a diverse set of biological reactions in low-G+C Gram-positive bacteria (Firmicutes). Here, we identify three predicted structural homologs of the RRNPP family, EF0073, EF1599, and EF1316, which affect biofilm formation and CAUTI pathogenesis.

Efficacy of Lytic Phage Cocktails on Staphylococcus aureus and Pseudomonas aeruginosa in Mixed-Species Planktonic Cultures and Biofilms

The efficacy of phages in multispecies infections has been poorly examined. The in vitro lytic efficacies of phage cocktails AB-SA01, AB-PA01, which target Staphylococcus aureus and Pseudomonas aeruginosa, respectively, and their combination against their hosts were evaluated in S. aureus and P. aeruginosa mixed-species planktonic and biofilm cultures. Green fluorescent protein (GFP)-labelled P. aeruginosa PAO1 and mCherry-labelled S. aureus KUB7 laboratory strains and clinical isolates were used as target bacteria. During real-time monitoring using fluorescence spectrophotometry, the density of mCherry S. aureus KUB7 and GFP P. aeruginosa PAO1 significantly decreased when treated by their respective phage cocktail, a mixture of phage cocktails, and gentamicin. The decrease in bacterial density measured by relative fluorescence strongly associated with the decline in bacterial cell counts. This microplate-based mixed-species culture treatment monitoring through spectrophotometry combine reproducibility, rapidity, and ease of management. It is amenable to high-throughput screening for phage cocktail efficacy evaluation. Each phage cocktail, the combination of the two phage cocktails, and tetracycline produced significant biofilm biomass reduction in mixed-species biofilms. This study result shows that these phage cocktails lyse their hosts in the presence of non-susceptible bacteria. These data support the use of phage cocktails therapy in infections with multiple bacterial species.

Fluorescent reporter plasmids for single-cell and bulk-level composition assays in E. faecalis

Fluorescent reporters are an important tool for monitoring dynamics of bacterial populations at the single cell and community level. While there are a large range of reporter constructs available–particularly for common model organisms like E. coli–fewer options exist for other species, including E. faecalis, a gram-positive opportunistic pathogen. To expand the potential toolkit available for E. faecalis, we exchanged the original fluorescent reporter in a previously developed plasmid (pBSU101) with one of eight fluorescent reporters and confirmed that all constructs exhibited detectable fluorescence in single E. faecalis cells and mixed biofilm communities. To identify promising constructs for bulk-level experiments, we then measured the fluorescence spectra from E. faecalis populations in microwell plate (liquid) cultures during different phases of aerobic growth. Cultures showed density- and reporter-specific variations in fluorescent signal, though spectral signatures of all reporters become clear in late-exponential and stationary-phase populations. Based on these results, we identified six pairs of reporters that can be combined with simple spectral unmixing to accurately estimate population composition in 2-strain mixtures at or near stationary phase. This approach offers a simple and scalable method for selection and competition experiments in simple two-species populations under aerobic growth conditions. Finally, we incorporated codon-optimized variants of blue (BFP) and red (RFP) reporters and show that they lead to increased fluorescence in exponentially growing cells. As a whole, the results inform the scope of application of different reporters and identify both single reporters and reporter pairs that are promising for fluorescence-based assays at bulk and single-cell levels in E. faecalis.

Role of FAD-I in Fusobacterial Interspecies Interaction and Biofilm Formation

: RadD, a major adhesin of oral fusobacteria, is part of a four-gene operon encoding the small lipoprotein FAD-I and two currently uncharacterized small proteins encoded by the rapA and rapB genes. Previously, we described a role for FAD-I in the induction of human B-defensin 2 (hBD2) upon contact with oral epithelial cells. Here, we investigated potential roles for fad-I, rapA, and rapB in interspecies interaction and biofilm formation. Gene inactivation mutants were generated for each of these genes in the nucleatum and polymorphum subspecies of Fusobacterium nucleatum and characterized for their adherence to partner species, biofilm formation, and operon transcription. Binding to Streptococcus gordonii was increased in all mutant strains with Δfad-I having the most significant effect. This increased adherence was directly proportional to elevated radD transcript levels and resulted in significantly different architecture and height of the biofilms formed by Δfad-I and S. gordonii compared to the wild-type parent. In conclusion, FAD-I is important for fusobacterial interspecies interaction as its lack leads to increased production of the RadD adhesin suggesting a role of FAD-I in its regulation. This regulatory effect does not require the presence of functional RadD.

Fluorescence Tools Adapted for Real-Time Monitoring of the Behaviors of Streptococcus Species

Tagging of bacteria with fluorescent proteins has become an essential component of modern microbiology. Fluorescent proteins can be used to monitor gene expression and biofilm growth and to visualize host-pathogen interactions. Here, we developed a collection of fluorescent protein reporter plasmids for Streptococcus mutans UA159 and other oral streptococci. Using superfolder green fluorescent protein (sfGFP) as a reporter for transcriptional activity, we were able to characterize four strong constitutive promoters in S. mutans These promoter-sfgfp fusions worked both for single-copy chromosomal integration and on a multicopy plasmid, with the latter being segregationally stable in the absence of selective pressure under the conditions tested. We successfully labeled S. mutans UA159, Streptococcus gordonii DL1, and Streptococcus sp. strain A12 with sfGFP, DsRed-Express2 (red), and citrine (yellow). To test these plasmids under more challenging conditions, we performed mixed-species biofilm experiments and separated fluorescent populations using fluorescence-activated cell sorting (FACS). This allowed us to visualize two streptococci at a time and quantify the amounts of each species simultaneously. These fluorescent reporter plasmids add to the genetic toolbox available for the study of oral streptococci.IMPORTANCE Oral streptococci are the most abundant bacteria in the mouth and have a major influence on oral health and disease. In this study, we designed and optimized the expression of fluorescent proteins in Streptococcus mutans and other oral streptococci. We monitored the levels of expression and noise (the variability in fluorescence across the population). We then created several fluorescent protein delivery systems (green, yellow, and red) for use in oral streptococci. The data show that we can monitor bacterial growth and interactions in situ, differentiating between different bacteria growing in biofilms, the natural state of the organisms in the human mouth. These new tools will allow researchers to study these bacteria in novel ways to create more effective diagnostic and therapeutic tools for ubiquitous infectious diseases.

The Combined Use of Tea Polyphenols and Lactobacillus Plantarum ST8SH Bacteriocin in a Rabbit Model of Infection Following Femoral Fracture with Internal Fixation

Background

Worldwide, the increasing use of antibiotics has resulted in antimicrobial resistance, leading to studies to find alternative antimicrobial treatments. Tea polyphenols have antibacterial properties. Bacteriocins produced by probiotic lactobacilli can inhibit Gram-positive bacteria. This study used a rabbit model of infection, following femoral fracture with internal fixation, to evaluate the efficacy of the combined use of tea polyphenols and Lactobacillus plantarum ST8SH bacteriocin.

Material/Methods

Twenty-four New Zealand White rabbits underwent femoral fracture, internal fixation, and insertion of a mini-titanium implant, and were inoculated intravenously with suspensions of Staphylococcal bacteria. Four treatment groups included group A, injected with tea polyphenols and bacteriocins (N=6); group B, injected with cefradine and bacteriocins (N=6); group C, injected with tea polyphenols and cefradine (N=6); and group D (controls), injected with saline (N=6). Blood samples were collected at 1, 6, 12, 24, and 48 hours after the injection of bacteriocins. Biofilms that formed on the mini-titanium implant were studied by fluorescence microscopy. Serum levels of level of interleukin (IL)-8, IL-6, and tumor necrosis factor-α (TNF-α) were measured using an enzyme-linked immunosorbent assay (ELISA).

Results

The combination of tea polyphenols and bacteriocins (group A) had a significant inhibitory effect on Staphylococcus aureus (P<0.05) and significant differences in serum levels of IL-8, TNF-α, and IL-6 levels in serum (P<0.05) when compared with groups, B, C, and D.

Conclusions

In a rabbit model of femoral fracture with internal fixation, the combined use of tea polyphenols and Lactobacillus plantarum ST8SH bacteriocin effectively controlled Staphylococcus aureus infection.

Streptococcus sanguinis biofilm formation & interaction with oral pathogens

Caries and periodontitis are the two most common human dental diseases and are caused by dysbiosis of oral flora. Although commensal microorganisms have been demonstrated to protect against pathogens and promote oral health, most previous studies have addressed pathogenesis rather than commensalism. Streptococcus sanguinis is a commensal bacterium that is abundant in the oral biofilm and whose presence is correlated with health. Here, we focus on the mechanism of biofilm formation in S. sanguinis and the interaction of S. sanguinis with caries- and periodontitis-associated pathogens. In addition, since S. sanguinis is well known as a cause of infective endocarditis, we discuss the relationship between S. sanguinis biofilm formation and its pathogenicity in endocarditis.

ciaR impacts biofilm formation by regulating an arginine biosynthesis pathway in Streptococcus sanguinis SK36

Streptococcus sanguinis is an early colonizer of the tooth surface and competes with oral pathogens such as Streptococcus mutans to maintain oral health. However, little is known about its mechanism of biofilm formation. Here, we show that mutation of the ciaR gene, encoding the response regulator of the CiaRH two-component system in S. sanguinis SK36, produced a fragile biofilm. Cell aggregation, gtfP gene expression and water-insoluble glucan production were all reduced, which suggested polysaccharide production was decreased in ΔciaR. RNA sequencing and qRT-PCR revealed that arginine biosynthesis genes (argR, argB, argC, argG, argH and argJ) and two arginine/histidine permease genes (SSA_1568 and SSA_1569) were upregulated in ΔciaR. In contrast to ΔciaR, most of strains constructed to contain deletions in each of these genes produced more biofilm and water-insoluble glucan than SK36. A ΔciaRΔargB double mutant was completely restored for the gtfP gene expression, glucan production and biofilm formation ability that was lost in ΔciaR, indicating that argB was essential for ciaR to regulate biofilm formation. We conclude that by promoting the expression of arginine biosynthetic genes, especially argB gene, the ciaR mutation reduced polysaccharide production, resulting in the formation of a fragile biofilm in Streptococcus sanguinis.

S. oralis activates the Efg1 filamentation pathway in C. albicans to promote cross-kingdom interactions and mucosal biofilms

Candida albicans and Streptococcus oralis are ubiquitous oral commensal organisms. Under host-permissive conditions these organisms can form hypervirulent mucosal biofilms. C. albicans biofilm formation is controlled by 6 master transcriptional regulators: Bcr1, Brg1, Efg1, Tec1, Ndt80, and Rob1. The objective of this work was to test whether any of these regulators play a role in cross-kingdom interactions between C. albicans and S. oralis in oral mucosal biofilms, and identify downstream target gene(s) that promote these interactions. Organotypic mucosal constructs and a mouse model of oropharyngeal infection were used to analyze mucosal biofilm growth and fungal gene expression. By screening 6 C. albicans transcription regulator reporter strains we discovered that EFG1 was strongly activated by interaction with S. oralis in late biofilm growth stages. EFG1 gene expression was increased in polymicrobial biofilms on abiotic surfaces, mucosal constructs and tongue tissues of mice infected with both organisms. EFG1 was required for robust Candida-streptococcal biofilm growth in organotypic constructs and mouse oral tissues. S. oralis stimulated C. albicans ALS1 gene expression in an EFG1-dependent manner, and Als1 was identified as a downstream effector of the Efg1 pathway which promoted C. albicans-S. oralis coaggregation interactions in mixed biofilms. We conclude that S. oralis induces an increase in EFG1 expression in C. albicans in late biofilm stages. This in turn increases expression of ALS1, which promotes coaggregation interactions and mucosal biofilm growth. Our work provides novel insights on C. albicans genes which play a role in cross-kingdom interactions with S. oralis in mucosal biofilms.

Identification and characterization of a novel Fusobacterium nucleatum adhesin involved in physical interaction and biofilm formation with Streptococcus gordonii

To successfully colonize the oral cavity, bacteria must directly or indirectly adhere to available oral surfaces. Fusobacterium nucleatum plays an important role in oral biofilm community development due to its broad adherence abilities, serving as a bridge between members of the oral biofilm that cannot directly bind to each other. In our efforts to characterize the molecular mechanisms utilized by F. nucleatum to physically bind to key members of the oral community, we investigated the involvement of F. nucleatum outer membrane proteins in its ability to bind to the pioneer biofilm colonizer, Streptococcus gordonii. Here, we present evidence that in addition to the previously characterized fusobacterial adhesin RadD, the interaction between F. nucleatum ATCC 23726 and S. gordonii V288 involves a second outer membrane protein, which we named coaggregation mediating protein A (CmpA). We also characterized the role of CmpA in dual‐species biofilm formation with S. gordonii V288, evaluated growth‐phase‐dependent as well as biofilm expression profiles of radD and cmpA, and confirmed an important role for CmpA, especially under biofilm growth conditions. Our findings underscore the complex set of specific interactions involved in physical binding and thus community integration of interacting bacterial species. This complex set of interactions could have critical implications for the formation and maturation of the oral biofilms in vivo, and could provide clues to the mechanism behind the distribution of organisms inside the human oral cavity.