Exam Bank Questions

Why is it important for DH to have good understanding of microorganisms?

Understand oral diseases → Microbes stick to surfaces & leads to gingivitis and perio → immune system reaction

Prevent infection → dental procedures can expose pts to microbes

Maintain infection control → knowledge of microbes help DH properly use sterilization, disinfection, PPE, hand hygiene

Protect pt → some pt have weakened immune system, infectious diseases

Compare & contrast prokaryotic & eukaryotic cells

Prokaryotic:

• No nucleus

• No organelles

• Cell wall: Peptidoglycan

• Reproduction: Binary fission

• 1 circular chromosome

Eukaryotic:

• Nucleus

• Organelles

• Cell wall: cellulose/chitin

• Reproduction: Mitosis

• Linear chromosome

What are the unique characteristics of bacteria?

Size

• Very small, can 2.4×10^11 bacteria /gm of plaque

• Large surface to volume ratio → rapid growth + transport

• Inhabit vv small ecosystems (dentinal tubules)

• Mechanical removal can be difficult

• Many diverse species @ single site

Metabolically Diverse

• Use full spectrum of nutrients (Carbs, protein, lactate, nylon tires)

  Live w or w/out oxygen (aerobic or anaerobic)

Adaptable

• Great opportunity for genetic change

• Short generation time (time it takes to reproduce) → can divide up to every 40 minutes

• Mutation rate 1/106

• Genetic info exchanged rapidly

  • If you give antibiotics, doctors tell you to take them all at once or within a time period because if you don’t, it gives them time to adapt and genetically change so they can become resistant

  • After becoming resistant, the bacteria can also pass on the gene

Ubiquitous

• Ubiquitous → present, appearing, found everywhere at the same time

  • Present in virtually all environments

    • Hot underwater fissures that are 300 degrees

    • Soil, air

    • Humans → Skin, nose, GI Tract, Genital tract, oral cavit

What does the term “metabolically diverse” mean when describing bacteria?

Explain how bacterial metabolic diversity contributes to their ability to survive in diff environments

Bacteria are able to use full spectrum of nutrients (Carbs, protein, lactate, nylon tires)

Can live w or w/out oxygen (aerobic or anaerobic)

What was the traditional method of classifying bacteria

1. Staining

• Gram stain (Gram + or -)

• Ziehl Neelsen → stain used to ID acid-fast bacteria like Mycobacteria tuberculosis

• Silver Impregnation staining → Treponema pallidum

2. Shape

• Microscopic

  • Spherical (cocci)

  • Rod (baccili)

• Macroscopic

  • Colony

3. Nutritional Characteristics

• What nutrients they consume

• Bacteriodes melanogenicus asaccharolyticus → does not ferment carbohydrates

• Bacteriodes melanogenicus intermedius → ferments carbohydrates

4. Fermentation end product

• Lactobaccilus species ferments glucose to lactic acid

5. Cell Wall Comoposition

• Ex. Streptococci subdivided based on cell-wall antigens (A-H) w/ the Lancefield Serotypes

6. DNA Base Composition

• Molar Fractions G+C/G+C+A+T

• Calculating the % of DNA ratios

7. Bacteriophage Bacterial virus susceptibility

• Classifying bacteria based on whether they are susceptible to certain viruses

8. Plasmid transfer

• Plasmids= small sections of DNA, can be transferred b/w similar grps of bacteria

• This is the reason for why bacteria can become resistant to antibiotics

• Ex. Enterobacteriaceae bcs bacteria in this family carry plasmids

What are the limitations of traditional bacterial classification and culture-based methods

No sensitivity & poor specificity

1. Does not ID huge uncultivated majority of microbes

• Location: Difficulties in sampling due to physical environment

• Organisms mb not capable of adapting in laboratory culture

  • Lack of essential nutrients, physiological needs/growth factors in culture media. overfeeding, toxicity in culture, inhibitory substances produced by other bacteria, metabolic dependance on other species, disruption of quorum-sensing systems (comm system b/w bacteria to track population density) induced by separation of bacteria, cell in low metabolic state (dormant)

• KEY idea is that when you take a sample somewhere, there is thousands of species of bacteria, but you don’t capture all of them, then when you grow them some of them are unable to grow in standard laboratory conditions

2. Even after successful cultivation, may not be successfully identified

• In the traditional method, identification mb heavily based on phenotypic (observable) characteristics, which you compare to reference slides but its so subjective, it might be done incorrectly → Misidentification

Why are some microbes unable to adapt to laboratory conditions?

• Organisms mb not capable of adapting in laboratory culture

  • Lack of essential nutrients, physiological needs/growth factors in culture media. overfeeding, toxicity in culture, inhibitory substances produced by other bacteria, metabolic dependance on other species, disruption of quorum-sensing systems (comm system b/w bacteria to track population density) induced by separation of bacteria, cell in low metabolic state (dormant)

• KEY idea is that when you take a sample somewhere, there is thousands of species of bacteria, but you don’t capture all of them, then when you grow them some of them are unable to grow in standard laboratory conditions

What is 16sRNA and why is it important in bacterial identification and classification?

16sRNA=part of machinary that bacteria uses to make proteins from amino acids

16sRNA when bound to ribosomal proteins make 30S subunit of ribosome

Gene that codes for 16sRNA found in all bacteria, part of sequence = conserved, so once the scientist find the conserved part, they can amplify it and look at the variable gene sections to classify the bacteria

• Stable + present in all organisms

• Sequence must be conserved sufficiently that regions of homology can be clearly established

• Must be sufficiently large that info is adequate to make phylogenetic inferences

What is the modern method used to determine bacterial classification & ID bacterial species?

Using gene and molecular biology with 16sRNA and PCR (Polymerase chain reaction) to amplify the DNA

You can use 16S rRNA to determine phylogeny of bacteria (relationship of organisms based on evolution)

• Can be used for accurate & rapid identification of known bacterial species (PCR)

• 16S rRNA to differentiate, quantify, classify unknown species (esp those that cannot be cultivated)

• Can be used for phylogenetic reclassification (classifying organism based on how evolutionary related they are) because similar 16sRNA= more similar

• Classifying microbes based on evolutionary relationship = more stable, less likely to need additional revision

• 16sRNA= documents evolutionary history >2000 sequences determined for bacteria but 16sRNA makes up only 0/05% of the genome

What is the mechanism of polymerase chain reaction (PCR)?

Requires:

• Template DNA → DNA w/ target sequence

• Primers → short DNA sequence that defines region to be amplified

• DNA polymerase → heat-stable enzyme like Taq polymerase

• Nucleotides (dNTPs) → building block for new DNA

• Buffers + ions like Mg3+

3 Steps

1. Denaturation ~95C

• Double stranded DNA separate into 2 single strands

2. Annealing ~50-65C

• Primer bind to complementary sequence on DNA strands

3. Extension ~72C

• DNA polymerase extends the primers and synthesizes new DNA strands

3 steps repeated 25-40 cycles, bcs DNA approx doubles each cycle, target sequence increases exponentially, generated millions of copies

Rapidly identifies viruses like HIV, Hepatitis…if you get poked by needle this is what is used

What are the two major pathways used by bacteria to generate ATP?

CONFIRM W/ NAJAR

Fermentation

• No electron transport chain

• ATP produced thru substrate-lvl phosphorylation

• Organic molecule= final electron acceptor

• Net gain= 2 ATP

• Used by subg plaque

Respiration

• Electron transport chain

• ATP produced thru oxidative phosphorylation

• External final electron acceptor

  • Aerobic= O2 is final electron acceptor

  • Anaerobic= Nitrate is final e- acceptor

• Net gain= 38 ATP

How much ATP can be generated thru cellular resp compared w/ fermentation?

Cellular resp can generate 38 ATP and fermentation only 2 ATP

Which is more energetically efficient for bacteria: cellular respiration or fermentation?

Cellular resp=more NRG efficient than fermentation bcs it uses

• Glycolysis

• Electron transport chain

• Oxidative phosphorylation

BUT fermentaiton can be advantageous with external electron acceptor=unavailable bcs bacteria can cont producing ATP w/out electron transport chain

Compare & contrast obligate aerobes, obligate anaerobes, facultative anaerobes, aerotolerant anaerobes

Obligate aerobes= Require O2

Obligate Anaerobes= die in O2

Facultative anaerobes= Respire in O2, ferment other wise (SWITCH)

Aerotolerant Anaerobes= Always ferment BUT have limited capacity to detoxify partial reduction products of O2

What are the sources of carbon and NRG for chemoheterotrophic bacteria?

Chemoheterotrophs include animals, fungi, and most other bacteria

Use oxidation-reduction reactions to produce ATP

Use organic molecules to supply itself with oxygen

What are Koch’s postulates

1. Microorganism must be demonstrable in all cases of disease

2. Microorganism must be isolated from diseased animal + grown in pure culture

3. Microorganism from pure culture must cause disease when inoculated into healthy animal

4. Experimentally infected animal must contain microorganism

What are the limitations or problems associated with Koch’s postulates?

Not all diseases are caused by microbes!!!

Auto-immune

Cancer

Asymptomatic

For Perio=

1. Inability to culture all organisms

2. Difficulties defining + culturing sites of active disease

3. Lack of animal model system

What is Socransky’s criteria?

Criteria for whether a microbe can be considered a periodontal pathogen

1. Must be associated w/ disease → increase in # of organisms at diseased site

2. Must be eliminated/decreased in sites that demonstrate clinical resolution of disease w/ treatment (mechanical or antibiotics)

3. Must demonstrate host response (alteration in host cellular or humoral immune response)

4. Must be capable of causing disease in experimental animal model

5. Must demonstrate virulence factors responsible to enable microbe to cause destruction of periodontal tissue

Name 6 bacterial species commonly found in root canals associated w/ teeth w/ necrotic pulp

Eurobacterium

Lactobacilli spp

Enterococcus

Streptococcus

Actinomyces spp

Peptostreptococcus

Name 5 bacterial species commonly associated with periodontal disease CONFIRM if genus or species

Eikenella

Clostridium

Porphyromonas

Selenomona

Actinobacillus

What is the causative organism of oral thrush (oral candidiasis)? Identify the organism and explain what the presence of oral thrush may indicate about the patient's underlying health or immune status.

DK YET

What factors affect microbial growth in oral cavity?

1. Temperature

• Human mouth is 35-36C affects bacterial metabolism, enzyme activity, habitat

2. Redox potential (anaerobiosis)

• Gradients of O2 [ ] and Eh(redox potential) exist in plaque in oral cavity

  • Some areas in plaque high in O2, deeper= lower

• Affects type of microbes that can be found

3. pH

• Most microbes require pH ~7 (Regulated by saliva)

4. Nutrients

• Endogenous saliva → Can be both + and -, helps bring in WBCs but also helps microbes grow by regulating the environment for them

• Exogenous saliva → What we eat

5. Adherence

• Chewing + saliva will detach

• Soft tissue desquamation limits bacterial load

• Hard tissue=high biofilm

6. Antimicrobial agents & inhibitors

• Dentifrices

• Mouth rinses

• Antibiotics

7. Host defences

• Innate immunity

• Non-specific immunity

• Specific immunity

What properties of the oral cavity make it suitable habitat for microbial growth?

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