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Multi-species Biofilms Biofilms • A biofilm is a community of microorganisms, associated with a surface, and encased in an extracellular polymeric matrix. Why is Biofilm Formation Important? • Many, if not the majority of infections involve biofilm formation (particularly chronic infections) • Important in device-related infections • Biofilm formation can complicate therapy Dental Biofilms QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. • Very complex community; multi-species, multi-kingdom • Develop in stages Acquired Pellicle Acquired Pellicle Tooth surface Tooth surface Stage 1: Pellicle formation Acquired Pellicle Tooth surface Stage 2: Initial Adherence Acquired Pellicle Tooth surface Stage 3: Aggregation Stage 4: Maturation Acquired Pellicle Tooth surface Stage 5: Dispersal Stage 1: Pellicle formation Stage 2: Initial Adherence Streptococci Actinomyces Acquired Pellicle Tooth surface Streptococci and Actinomyces are initial colonizers Stage 1: Adherence • Why is adherence important? – Adherence is a critical first step in pathogenesis. – All pathogenic bacteria produce adhesins • What is an adhesin? – ADHESIN: Bacterial macromolecule that binds to specific ligands or receptors on host cells and defines the tropism of the microbe for various cells or tissues. Role of adherence 1) To avoid physical removal by host defenses – Mucociliary escalator – Washing action of saliva tears, mucus – Blood and urine flow 2) To make intimate contact with host tissues – Nutrient uptake – Invasion Types of Adhesins 1. Pili / fimbriae 2. Non-pilus surface proteins 3. Polysaccharides Types of Adhesins; 1. Pili • Streptococcus pyogenes pilus promotes adhesion to pharyngeal epithelial cells. • This is necessary for streptococcal pharyngitis Types of adhesins; 2. Surface Proteins • S. gordonii: Amylase-binding protein, AbpA S. gordonii Types of adhesins; 3. Polysaccharides • e.g. S. mutans produces glucosyltransferases that convert sucrose into polysaccharides which; – 1. Act as receptors for adhesins on other bacteria – 2. Contribute to adherence of S. mutans to the tooth surface Approaches to reducing adherence • Physical disruption; oral hygiene. • Replacing sucrose with nonutilizable sugars. • Anti-adhesin vaccines Stage 3: Aggregation Acquired Pellicle Tooth surface QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture. Stage 4: Maturation Acquired Pellicle Tooth surface • Increased species diversity; late colonizers Co-aggregation • Mediated by interactions between lectins on one bacterial cell and sugar residues on another. Co-aggregation Bacterial Vaginosis (BV) • Most common vaginal disorder worldwide • Mixed species biofilm forms on the vaginal epithelium Normal vaginal secretions BV vaginal secretions BV Associated Risk Factors • Number of known risk factors including – – – – – Sexual activity and number of sexual partners IUD usage Douching Antibiotic treatment Smoking Diagnosis • Wet mount: prepared from vaginal sample and observed for presence of clue cells • Whiff test with KOH • Vaginal pH greater than 4.5 • Culture or Gram stain • Positive 3 out of 4 is indicative of BV, treatment with oral or topical Metronidazole Complications of BV – Preterm delivery, low birth weight – Complications during pelvic surgeries can lead to PID – Increased risk of infection with HIV and other STDs – Frequently relapses or recurs after treatment Etiology of BV • G. vaginalis is the predominant species in >= 90% of cases, but pure cultures don’t reliably cause infection • Koch’s postulates have not been satisfied • Is G. vaginalis necessary but not sufficient to cause the disease?? Gardnerella vaginalis • Facultative anaerobe, Gram positive or variable, rod shaped • Non-motile, non-flagellated, non-spore forming, nonencapsulated, may produce pili • G. vaginalis forms a biofilm on the vaginal epithelium of women with bacterial vaginosis (BV) Electron microscopy of G. vaginalis Hypothesis • Similar to Streptococci in dental biofilms, G. vaginalis is an initial colonizer and forms a biofilm on the vaginal epithelium. Biofilm formation allows G. vaginalis and other anaerobic species to survive in the face of oxygen, acid, hydrogen peroxide, and immune factors in the vagina. How would a biofilm limit local O2 concentrations? Forces of diffusion and convection (mixing) Forces of diffusion and convection (mixing) Forces of diffusion and convection (mixing) Forces of diffusion and convection (mixing) Forces of diffusion and convection (mixing) Forces of diffusion and convection (mixing) Mathematical Modeling of Biofilms • Is our hypothesis valid? • Could biofilm formation by G. vaginalis sufficiently deplete local oxygen concentrations?