Chapter 11 Flashcards
1
Q
Microbe
A
- Refers to all types of microscopic organisms (bacteria, fungi, protozoa, viruses)
Not all microbes pathogenic
2
Q
General characteristics of bacteria
A
- smallest, simplest organisms viewable only through microscope
- most dominant living organisms on planet
- have existed longer than any other life on planet
- reproduce quickly and adapt quickly
Enhanced bacterial survival and reproduction in host
3
Q
Structure of the Bacterial cell envelope
A
- Complex multilayered structure that protects microorganism from unpredictable and inhospitable external environment
- Gram staining
Classifies bacteria based on cell envelope structure
All bacteria either gram-positive or gram-negative
4
Q
Gram staining
A
-Depending on permeability of stain through cell envelope, when viewed under light microscope, bacteria appear either:
- Purple (positive)
- Pink (negative)
5
Q
Gram-positive bacteria (purple)
A
- Single thick multilayered mesh like cell wall composed of peptidoglycan
Lies above cytoplasmic membrane facing interior of cell
Binds and retains purple color when stained with crystal violet dye
6
Q
Gram-Negative bacteria (pink)
A
- Outer membrane faces external environment
Composed of proteins and lipopolysacharides
LPS play major role in pathogenesis of gram-negative bacterial infections - Inner cytoplasmic membrane faces interior of cell
- Thin, single-layer cell wall between membranes
Made of peptidoglycan; does not readily absorb violet dye
7
Q
Bacteria are “social creatures”
A
-Interact with one another
- Live together in complex microbial communities
Contain different species of microbes that are spatially organized within community
8
Q
Microbial communities
A
- Most microbes live in complex poly microbial biofilm communities attached to living or nonliving surfaces
- What is biofilm
Complex, dynamic microbial community embedded within matrix adhered to living or nonliving surface
MAy be responsible for 65% of diseases
9
Q
Where do biofilms form
A
- Everywhere in nature
- Can exist on any solid surface exposed to microbe-containing fluid
0 Can be prevalent in natural, industrial and hospital settings
10
Q
Typical Timeline for biofilm formation
A
Within minutes:
- Free floating microbes attach to surface
Within 2-4 hours:
-Microbes form strongly attached micro colonies
Within 6-12 hours:
- Microbes produce initial extracellular matric
11
Q
Hoe do mature biofilms protect bacteria
A
- Blocking
Preventing large molecules from penetrating matrix - Mutual protection
Protecting one another (and sometimes host) - Hibernation (quiescence)
Laying dormant until conditions become more favorable
12
Q
Oral biofilms
A
Polymicrobial, three-dimensial community embedded in protective matrix that consists of microbial metabolic products and/or host componens
13
Q
Resident microbes of the oral cavity
A
- Commensal bacteria are part of normal flora in mouth
Prevent colonization by opportunistic pathogenic bacteria
Comprise biofilm found on all epithelial-lined surfaces - Symbiotic relationship with host
Contribute to host nutrition, maintain robust immune system and provide cover over mucous membranes
Host provides nutrients, stable environment for survival
14
Q
Early dysbiosis
A
-Dysbiosis is microbial imbalance on or inside body
Can result if certain species of microbes become dominant
Occurs when oral biofilm not disrupted frequently
Leads to gingival inflammation
15
Q
Established dysbiosis
A
- symbiotic host-microbe relationship becomes pathogenic
-triggers inappropriate, excessive host response that results in irreversible periodontal tissue damage
16
Q
Control of microbial growth within a mature oral biofilm
A
- Biofilm bacteria resistant to antibiotics and antimicrobial agents
Works best when combined with mechanical cleaning - Physicial removal of dental plaque biofilms essential
Breaks up biofilm, forces bacteria to start over
Periodontal instrumentation needed for subgingival plaque
17
Q
Transmission of Biofilm bacteria
A
- Transmissible via direct or indirect contact
- Most common route is vertical transmission (via sharing saliva between caregiver and child)
- Less common route is horizontal transmission (via individuals of same generation kissing)
- Periodontal pathogens transmissible, but periodontal disease not an infectious disease
18
Q
Examples of gram-positive species capable of colonizing the mouth
A
- Streptococcus
-Peptostreptococcus
-Actinomyces
-Rothia
-Eubacterium
-Mycoplasma
19
Q
Example of Gram-Negative species capable of colonizing the mouth
A
- Neisseria
- Veillonella
-Aggregatibacter
-Campylobacter
-Prevotella
-Spirochètes of ANUG
20
Q
Stages of polymicrobial biofilm formation
A
- initial attachement
- Irréversible attachment
- maturation 1
- Maturation 2
- Dispersion
21
Q
Stage 1: initial attachment of microbes to pellicle
A
- Acquired salivary pellicle immediately forms over clean tooth surface
- Free-floating microbes attach using fimbriae
- initial attachment dynamic and reversible
22
Q
Stage 2: Permanent attachment
A
- Attained by microbes that can weather hydrodynamic forces and maintain steadfast grip on tooth surface
- Microbes begin producing substances that attract other free-floating bacteria to community
- Process is called coaggregation
23
Q
Stage 3: Maturation phase 1: self-protective matrix formation
A
- Attached bacteria secrete extracellular protective matrix that protects against host immune défenses
Generally consists of proteins, glycolipids, and bacterial DNA
24
Q
Stage 4: Maturation Phase 2: mushroom shaped micro colonies
A
- Microcolony formation
Combination of cell division and recruitment
Microbes cluster, form mushroom-shaped micro colonies that exchange and share nutrients and genetic information
Environmental conditions within micro colonies vary radically, resulting in very diverse population
- Internal organization of mature biofilm
Layers and layers of microbes
Fluid channels form, penetrate extracellular matrix, and direct fluids into and around biofilm
Cell-to-cell communication using chemical signals
Bacteria communicate by releasing and sensing small proteins in process called quorum sensing
25
Stage 5: dispersion: escape from the matrix
- Essential stage of biofilm life cycle
- Dispersal enables biofilms to:
Spread, colonize new tooth surface
26
Bacterial colonization and succession of oral biofilms
- Sequence of bacterial colonization:
Early bacterial colonizers including many streptococcal species, release chemical signals indicating conditions favorable for joining biofilm
Favorable conditions necessary for microbes to join
Mature biofilm collection of multiple microbial species
27
Bacterial attachement zones
-Tooth surface and epithelial lining of periodontal pocket
-Tooth-associated plaque biofilms
Attached to tooth surface; can invade dentinal tubules
-Tissue-associated plaque biofilms
Adhere to epithelium; can invade gingival tissue
- Unattached bacteria
Free-floating; not part of biofilm
28
Changing evidence for the role of bacteria
- Five hypotheses to explain role in periodontal disease
Nonspecific plaque hypothesis
Specific plaque hypothesis
Ecological plaque hypothesis
Microbial homeostasis-host réponse hypothesis
Keystone pathogen-host response hypothesis
29
Historical pers;ective: nonspecific plaque hypothesis
- Overaccumulation of plaque biofilm at gingival margin leads to gingival inflammation and tissue destruction
-Limitations:
Too simplistic and superficial
Fails to explain why most. gingivitis never becomes periodontitis and some periodontitis involves little biofilm
30
Historical perspective: specific plaque/microbial shift hypothesis
- Oral microtobia shifts from primarily beneficial to primarily pathogenic as periodontitis develops
- increase in specific pathogens causes periodontitis
- Bacteira change from mainly gram-positive aerobic community to mainly gram-negative anaerobes
-Socransky’s microbial complexes
. Studies identified specific groups of interdépendant bacteria significantly associated with periodontitis
. Orange and red: periodontal disease
. Yellow, green, blue, and purple: gingival health
- Limitations:
Newer microbial assaying systems detected red-complex microorganisms in healthy, no diseases sites
Periodontal microbe population more heterogenous and diverse than previously thought
Gram-positive anaerobic bacteria found in deep periodontal pockets in greater numbers than gram-negative species
31
Current perspective: ecological plaque hypothesis
- Accumulation of nonspecific bacteria triggers host inflammatory response, altering local environment
- Environment becomes more conductive to growth of pathogenic bacteria
- Support for this hypothesis
. Sites with bleeding upon probing and deeper probing depths strongly associated with higher GCF flow, which alters microbial ecology, favoring pathogens
. Subgingival periodontal instrumentation alters subgingival ecosystem, reducing number of pathogens
32
Current perspective: Microbial Homeostasis Host response hypothesis
- Plaque biofilms cause initial inflammatory response leading to gingivitis, but pathogenic bacteria not direct cause of tissue destruction in periodontitis
- Support for this hypothesis
Biofilm microbe population associated with health remains stable over time, exists in state of biological equilibrium
Research fails to show bacterial pathogens directly and solely responsible for tissue destruction
Overwhelming evidence demonstrates uncontrolled host inflammatory and immune response causes tissue destruction seen in periodontitis
33
Current perspective: Keystone pathogen-host response hypothesis
- Specific bacterial species is key in creating shift from symbiotic microbes to dysbiosis microbes
- Dysbiosis biofilm community triggers uncontrolled host response that results in damage to periodontal tissues
- Support for this hypothesis:
Decades of research have failed to provide evidence that specific bacterial pathogens are direct cause of tissue destruction seen in periodontitis
Current evidence indicates uncontrolled host inflammatory and immune responses cause tissue destruction seen in periodontitis
34
Immune status of periodontal tissue between healthy and diseased patients
- Healthy tissue: mild subclinical inflammation
- Diseased tissue: disordered severe inflammation
- Shift from beneficial microbes to pathogenic community triggers potent host inflammatory response that contributes to tissue destruction and alveolar bone loss associated with periodontitis
