Microbial biofilms play a dominant role in the failure of endodontic therapies. Bacterial adhesion is the first step in the establishment of biofilms, activating the host immune response leading to tissue damage. Biosurfactants are microbe‐derived tensioactive molecules with latent anti‐adhesive and anti‐microbial activity. This study reports the extraction and characterization of a biosurfactant from Lactobacillus (L.) plantarum (Lp‐BS) and investigates its anti‐microbial and anti‐adhesive properties compared to rhamnolipid, a commercially available biosurfactant. Lp‐BS, extracted from L. plantarum during the growth phase, was characterized as a glycoprotein, able to reduce surface tension and emulsify non‐polar liquids. Proteomic analysis of Lp‐BS identified three bacterial adhesin‐like proteins, suggesting roles in hindering bacterial adhesion. Lp‐BS did not show significant anti‐microbial activity against endodontic pathogens from the Streptococcus (Strep.) anginosus group or Enterococcus (Ent.) faecalis at 50 mg/ml. However, anti‐adhesive activity on abiotic surfaces was observed against both Strep. anginosus and Strep. intermedius. Rhamnolipid exhibited strong anti‐microbial activity, with minimum inhibitory concentrations of 0.097 mg/ml against Strep. anginosus, and 0.048 mg/ml against Strep. constellatus and Strep. intermedius, in addition to a marked anti‐adhesive activity. These findings offer preliminary evidence for the potential application of biosurfactants as an anti‐microbial and/or anti‐adhesive pharmacotherapy in endodontics.

Introduction. Bacterial pneumonia is a common cause of morbidity and mortality in elderly individuals. While the incidence of edentulism is falling, approximately 19 % of the UK population wear a full or partial removable denture. Despite advances in denture biomaterials, the majority of dentures are fabricated using polymethyl-methacrylate. Growing evidence suggests that colonization of the oral cavity by putative respiratory pathogens predisposes individuals to respiratory infection, by translocation of these microorganisms along the respiratory tract. Hypothesis/Gap Statement. We hypothesized that denture surfaces provide a susceptible colonization site for putative respiratory pathogens, and thus could increase pneumonia risk in susceptible individuals. Aim. This study aimed to characterize the bacterial community composition of denture-wearers in respiratory health compared with individuals with a confirmed diagnosis of pneumonia. Methodology. This was an analytical cross-sectional study, comparing frail elderly individuals without respiratory infection (n=35) to hospitalized patients with pneumonia (n=26). The primary outcome was the relative abundance of putative respiratory pathogens identified by 16S rRNA metataxonomic sequencing, with quantitative PCR used to identified Streptococcus pneumoniae . Results. There was a statistically significant increase in the overall relative abundance of putative respiratory pathogens (P<0.0001), with a greater than 20-fold increase in the bioburden of these microorganisms. In keeping with these findings, there were significant shifts in bacterial community diversity (Chao index, P=0.0003) and richness (Inverse Simpson index P<0.0001) in the denture-associated microbiota of pneumonia patients compared with control subjects. Conclusion. Within the limitations of this study, our evidence supports the role of denture acrylic biomaterials as a potential colonization site for putative respiratory pathogens, which may lead to an increased risk of pneumonia in susceptible individuals. These findings support prior observational studies which have found denture-wearers to be at increased risk of respiratory infection. Further research is needed to confirm the sequence of colonization and translocation to examine potential causal relationships.

Background Bacterial pneumonia affects a disproportionate number of the elderly in the UK, with substantial morbidity and mortality. Mounting evidence implicates removable dentures as a potential nidus for respiratory pathogens to form a reservoir which could seed colonisation and infection of respiratory tissues in susceptible individuals. However, research evaluating the denture-associated microbiome in patients with an active diagnosis of pneumonia is lacking. The aim of this study was to characterise denture-associated oral bacterial communities by metataxonomic sequencing of 16S rRNA genes. The prevalence of antimicrobial resistance among two representative pathogenic species Staphylococcus aureus and Pseudomonas aeruginosa was also assessed. Finally, the role of salivary cytokines as diagnostic biomarkers was explored. Results There were significant shifts observed in species composition, diversity and richness in the denture-associated microbiome of pneumonia patients. Importantly, the relative abundance of putative respiratory pathogens in the denture-associated microbiota of pneumonia patients was significantly increased compared with respiratorily healthy care home residents. The magnitude of this increase was approximately three-fold in denture-associated bacterial communities compared with other oral sites examined. Antimicrobial resistance was equivocal between microbes isolated from both participant cohorts, highlighting the potential for oral biofilms to protect microbes from systemic antimicrobial therapy. While salivary cytokine profiles did not correlate with pneumonia status, the concentration of IL-6 and IL-8 positively correlated with the relative abundance of putative respiratory pathogens on denture surfaces. Conclusions This is the first study to directly examine compositional shifts in the denture-associated oral microbiome in respiratory infection, providing a basis for disentangling potential causal relationships.