Multi-species BiofilmsMulti-species Biofilms

BiofilmsBiofilms

• A biofilm is a A biofilm is a communitycommunity of of microorganisms, associated with a microorganisms, associated with a surface, and encased in an surface, and encased in an extracellular polymeric extracellular polymeric matrixmatrix..

Why is Biofilm Formation Why is Biofilm Formation Important?Important?

• Many, if not the majority of infections Many, if not the majority of infections involve biofilm formation involve biofilm formation (particularly chronic infections)(particularly chronic infections)

• Important in device-related infections Important in device-related infections

• Biofilm formation can complicate Biofilm formation can complicate therapytherapy

Dental BiofilmsDental Biofilms

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• Very complex Very complex community; community; multi-species, multi-species, multi-kingdommulti-kingdom

• Develop in Develop in stagesstages

Tooth surface

Acquired Pellicle

Stage 1: Pellicle formation Stage 2: Initial Adherence

Tooth surface

Acquired Pellicle

Stage 3: Aggregation

Tooth surface

Acquired Pellicle

Stage 4: Maturation

Tooth surface

Acquired Pellicle

Stage 5: Dispersal

Tooth surface

Acquired Pellicle

Stage 1: Pellicle formationStage 1: Pellicle formation

Stage 2: Initial AdherenceStage 2: Initial Adherence

Tooth surface

Acquired Pellicle

Streptococci Actinomyces

StreptococciStreptococci and and ActinomycesActinomyces are are initial colonizersinitial colonizers

Stage 1: AdherenceStage 1: Adherence

• Why is adherence important? Why is adherence important? – Adherence is a critical first step in Adherence is a critical first step in

pathogenesis.pathogenesis.

– All pathogenic bacteria produce adhesinsAll pathogenic bacteria produce adhesins

• What is an adhesin?What is an adhesin?– ADHESIN: Bacterial macromolecule that binds ADHESIN: Bacterial macromolecule that binds

to specific ligands or receptors on host cells to specific ligands or receptors on host cells and defines the tropism of the microbe for and defines the tropism of the microbe for various cells or tissues.various cells or tissues.

Role of adherenceRole of adherence

1) To avoid physical removal by host 1) To avoid physical removal by host defensesdefenses– Mucociliary escalatorMucociliary escalator– Washing action of salivaWashing action of saliva tears, mucustears, mucus– Blood and urine flowBlood and urine flow

2) To make intimate contact with host tissues2) To make intimate contact with host tissues– Nutrient uptakeNutrient uptake– InvasionInvasion

Types of AdhesinsTypes of Adhesins

1.1. Pili / fimbriaePili / fimbriae

2.2. Non-pilus surface proteinsNon-pilus surface proteins

3.3. PolysaccharidesPolysaccharides

Types of Adhesins; 1. PiliTypes of Adhesins; 1. Pili

• Streptococcus pyogenesStreptococcus pyogenes pilus promotes adhesion pilus promotes adhesion to pharyngeal epithelial to pharyngeal epithelial cells. cells.

• This is necessary for This is necessary for streptococcal pharyngitisstreptococcal pharyngitis

Types of adhesins; Types of adhesins; 2. Surface Proteins2. Surface Proteins

• S. gordoniiS. gordonii: Amylase-binding : Amylase-binding protein, AbpAprotein, AbpA

S. gordonii

Types of adhesins; Types of adhesins; 3. Polysaccharides3. Polysaccharides

• e.g. e.g. S. mutansS. mutans produces produces glucosyltransferases that convert glucosyltransferases that convert sucrose into polysaccharides which;sucrose into polysaccharides which;– 1. Act as receptors for adhesins on 1. Act as receptors for adhesins on

other bacteria other bacteria – 2. Contribute to adherence of 2. Contribute to adherence of S. mutansS. mutans

to the tooth surface to the tooth surface

Approaches to reducing Approaches to reducing adherenceadherence

• Physical disruption; oral hygiene.Physical disruption; oral hygiene.

• Replacing sucrose with non-Replacing sucrose with non-utilizable sugars.utilizable sugars.

• Anti-adhesin vaccinesAnti-adhesin vaccines

Stage 3: AggregationStage 3: Aggregation

Tooth surface

Acquired Pellicle

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Stage 4: MaturationStage 4: Maturation

Tooth surface

Acquired Pellicle

• Increased species diversity; late Increased species diversity; late colonizerscolonizers

Co-aggregationCo-aggregation

• Mediated by interactions between lectins on one bacterial cell and sugar residues on another.

Co-aggregationCo-aggregation

Bacterial Vaginosis (BV)Bacterial Vaginosis (BV)

• Most common vaginal Most common vaginal disorder worldwidedisorder worldwide

• Mixed species biofilm Mixed species biofilm forms on the vaginal forms on the vaginal epithelium epithelium Normal vaginal secretions

BV vaginal secretions

BV Associated Risk FactorsBV Associated Risk Factors

• Number of known risk factors includingNumber of known risk factors including– Sexual activity and number of sexual partnersSexual activity and number of sexual partners– IUD usageIUD usage– DouchingDouching– Antibiotic treatmentAntibiotic treatment– SmokingSmoking

DiagnosisDiagnosis

• Wet mount: prepared Wet mount: prepared from vaginal sample from vaginal sample and observed for and observed for presence of presence of clue cellsclue cells

• Whiff test with KOHWhiff test with KOH• Vaginal pH greater Vaginal pH greater

than 4.5than 4.5• Culture or Gram stain Culture or Gram stain • Positive 3 out of 4 is Positive 3 out of 4 is

indicative of BV, indicative of BV, treatment with oral or treatment with oral or topical Metronidazoletopical Metronidazole

Complications of BVComplications of BV

– Preterm delivery, low birth weightPreterm delivery, low birth weight– Complications during pelvic surgeries Complications during pelvic surgeries

can lead to PIDcan lead to PID– Increased risk of infection with HIV and Increased risk of infection with HIV and

other STDsother STDs– Frequently relapses or recurs after Frequently relapses or recurs after

treatmenttreatment

Etiology of BVEtiology of BV

• G. vaginalisG. vaginalis is the predominant is the predominant species in >= 90% of cases, but pure species in >= 90% of cases, but pure cultures don’t reliably cause cultures don’t reliably cause infectioninfection

• Koch’s postulates have not been Koch’s postulates have not been satisfiedsatisfied

• Is Is G. vaginalisG. vaginalis necessary but not necessary but not sufficient to cause the disease??sufficient to cause the disease??

Gardnerella vaginalisGardnerella vaginalis

• Facultative anaerobe, Gram Facultative anaerobe, Gram positive or variable, rod positive or variable, rod shapedshaped

• Non-motile, non-flagellated, Non-motile, non-flagellated, non-spore forming, non-non-spore forming, non-encapsulated, may produce encapsulated, may produce pilipili

• G. vaginalisG. vaginalis forms a biofilm on forms a biofilm on the vaginal epithelium of the vaginal epithelium of women with bacterial women with bacterial vaginosis (BV)vaginosis (BV)

Electron microscopy of G. vaginalis

HypothesisHypothesis

• • Similar to Streptococci in dental biofilms, Similar to Streptococci in dental biofilms, G. G. vaginalisvaginalis is an is an initial colonizerinitial colonizer and forms a biofilm and forms a biofilm on the vaginal epithelium. Biofilm formation on the vaginal epithelium. Biofilm formation allows allows G. vaginalisG. vaginalis and other anaerobic species to and other anaerobic species to survive in the face of oxygen, acid, hydrogen survive in the face of oxygen, acid, hydrogen peroxide, and immune factors in the vagina.peroxide, and immune factors in the vagina.

How would a biofilm limit How would a biofilm limit local Olocal O22 concentrations? concentrations?

Forces of diffusion and Forces of diffusion and convection (mixing)convection (mixing)

Forces of diffusion and Forces of diffusion and convection (mixing)convection (mixing)

Forces of diffusion and Forces of diffusion and convection (mixing)convection (mixing)

Forces of diffusion and Forces of diffusion and convection (mixing)convection (mixing)

Forces of diffusion and Forces of diffusion and convection (mixing)convection (mixing)

Forces of diffusion and Forces of diffusion and convection (mixing)convection (mixing)

Mathematical Modeling of BiofilmsMathematical Modeling of Biofilms

• Is our hypothesis valid?Is our hypothesis valid?

• Could biofilm formation by Could biofilm formation by G. G. vaginalisvaginalis sufficiently deplete local sufficiently deplete local oxygen concentrations?oxygen concentrations?