Lecture 2: Biofilm Microbiology

definition: a complex aggregation of microorganisms on a surface marked by excretion of protective and adhesive matrix

biofilm

T or F: all colonizing species are pathogenic

false; some are protective

plaque is (blank)% water and (blank)% solid material

• 80% water

• 20% solid material

the dry weight of plaque is (blank)% cellular and (blank)% extracellular

• 35% cellular

• 65% extracellular

what are the cellular components of oral biofilm (dry weight)?

mainly bacteria but also other microorganisms like yeast, virus, protozoa or host-derived cels lie epithelial, PMNs, macrophages

what are the extracellular components of oral biofilm (dry weight)?

• polysaccharides (95% dextrans=adhesion 5% levans=energy), proteins, glycoproteins, lipids, minerals: Ca, P, Na, K, F

◦ ↑mineral content = ↑calculus formation

definition: thin, acellular film formed on tooth surface and oral tissues when exposed to saliva, a protective layer

salivar pellicle

what are the two stages of oral biofilm formation?

reversible then more permanent adherence: planktonic → sessile due to bacterial phenotypic change

• planktonic = free float/suspension

• sessile = attached, immobile

what genes are turned ON during the slight lag of biofilm formation?

polysaccharide production

what genes are turned OFF during the slight lag of biofilm formation?

flagella

what type of polysaccharides do (single) bacteria on pellicle make during rapid growth?

water-insoluble

confluent micro-colonies that are fomed increase cell density in plaque; biofilm thicker due to cell division

definition: when bacteria in suspension adhere to each other and form clumps

coaggregation

definition: free-floating bacteria attach to already adhered bacteria

coadhesion

what are the four secondary colonizers that adhere to bacteria of plaque mass via coaggregation and coadherence?

• Prevotella intermedia

• Capnocytophaga spp

• Fusobacterium nucleatum

• Porphyromonas gingivalis

definition: early aerobic environment (gram-pos facultative) → oxygen-deprived (gram-neg anaerobic)

ecological succession

definition: metabolic products of pioneer plaque species modify immediate environment so new colonizers can inhabit plaque leading to increase in microbial complexity, biomass, & thickness

bacterial succession

defiition: plaque mass reaches critical size due to balance btwn deposition and loss of plaque bacteria is established

climax community

describe the organization of human supragingival plaque (3 key points)

1. stratified organization

2. surface: gram-pos cocci and rods

3. in plaque mass: gram-neg rods and spirochetes

highly ineractive cell-cell interactions

describe the organization of subgingival plaque (2 types)

1. tooth associated/attached plaque

2. tissue associated

describe organization of subgingival tooth associated/attached plaque:

• gram-pos rods and cocci dense and filamentous

• apical border of plaque mass separated from junctional epithelium by leukocytes, gram-neg rods

describe the organization of tissue associated plaque:

• plaque less organized and less dense

• gram-neg rods and cocci, filaments, flagellated rods and spirochetes; possibly host tissue cells too

T or F: all bacteria are equally capable of causing disease

false: *not all

T or F: free-floating bacteria do NOT cause disease

true: bacteria must attch to a surface to cause disease

T or F: bacteria found in dental plaque often behave much differently than when observed in lab or in culture

true

T or F: selective changes of either bacteria and/or host can lead to peridontal disease

true: the bacteria and host continuously interact in a dynamic equilibrium that is mostly protective until one side changes selectively

how many species of bacteria can be found in oral cavity?

1700+

how many species colonize the periodontal tissues?

400-500

T or F: severe periodontal disease is ALWAYS correlated with excessive plaque accumulation

false; *NOT always

definition: criteria to determine if organism causes disease

Koch’s postulates

what are the four Koch's postulates requirements?

1. bacteria must be isolated from diseased tissues

2. pure cultures must be obtained

3. organisms must cause disease in animals

4. organisms must be obtained from experimental animals

why is Koch’s postulates difficult to apply in periodontology?

bc it's designed for mono-infections, inability to culture all microorganisms, conceptual problems, lack of good animal models (there are asymptomatic carriers and viruses cannot be grown in ure culture, not universally applicable)

what is the modified Koch’s Postulates for Periodontology? (Socranksy)

• Putative pathogens must be found in large numbers in diseased sites

• Absence of pathogens in health

• Must be able to demonstrate an immune response to putative pathogens

• Virulence factors can often be demonstrated

• Animal models should simulate human disease

• Elimination of these organisms should result in clinical improvement

definition: out of diverse collection of organisms comprising resident plaque microflora only a few involved in disease

specific plaque hypothesis:

• control disease by targeting preventative measures and treat against limited number of organisms

definition: disease is outcome of overall activity of total plaque microflora

non-specific plaque hypothesis

• heterogeneous mixture of microorganisms could influence disease

definition: dynamic relationship btwn host environment and resident subgingival microbiota

ecological plaque hypothesis

• increase lvls biofilm leads to host inflam response which alters local enviro

• end: proteolytic and anaerobic enviro, predispose site to a disease (vs healthy are predominantly aerobic and facultative anaerobic)

what is considered the primary etiologic factor leading to inflammator disease of the gingiva and periodontitis?

bacteria

red complex consists of:

• P. gingivalis

• T. forsythensis

• T. denticola

gram positive or gram negative?

• Streptococcus sanguis

• Streptococcus mitus

• Actinomyces viscosus

• Actinomces israelii

• Actinomyces naeslundii

gram positive

gram positive or gram negative?

• Veillonella sp.

• Bacteroides sp.

• Neisseria sp.

• Fusobacterium sp

gram negative

healthy gingival sulcus composition:

• 85% gram positve

• 15% gram negative

• predominantly aerobic and facultative anaerobic

gingivitis composition:

• 56% gram positive

• 44% gram negative

• increasing anaerobic and facultative anaerobic

periodontitis composition:

• 19% gram positive

• 74% gram negative

• predominantly anaerobic

describe these microbial shifts during disease:

• gram poitive → ?

• cocci → ? → ?

• nonmotile → ?

• facultative anaerobes → ?

• gram poitive → gram negative

• cocci → rods → spirochetes

• nonmotile → motile

• facultative anaerobes → obligate anaerobes