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Stage 2 Microbiology for dentists > MFD3 > Flashcards

MFD3 Flashcards

1
Q

How do prokaryotes differ to eukaryotes?

A 
no internal membranes (organelles),
simple chromosomes (haploid), no histones
no fusion of gametes (can transfer DNA)
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2
Q

Give an example of a microbrial eukaryote:

A

fungi

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3
Q

How does fungi differ from bacteria:

A
  1. larger
  2. feeding – chemoorganotrophs (secrete extracellular enzymes that digest complex organic material)
  3. Can form a network of filaments (hyphae)
  4. Can grow across surfaces – tuft (mycelium)
  5. Spore forming tip (conidia= asexual spores)
  6. Structure :
    a) Rigid cell wall (chitin = tough wall, while in bacteria is peptidoglycan)
    b) Ergesterol rather than cholesterol in cell membrane
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4
Q

What is Mycelium ?

A

Mycelium is the vegetative part of a fungus or fungus-like bacterial colony, consisting of a mass of branching, thread-like hyphae.

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5
Q

1) What is Candidiasis ? where does it grow?

2) When does candidiasis occur?

A

1) Fungal infection of – GI system, vagina, oral cavity

2) Seen in states of immune suppression, when medical devices are in place, antibiotic use

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6
Q

Define endogenous bacteria + e.g

A

bacteria that naturally resides in a closed system, e.g. candidiasis

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7
Q

What are the different morphologies of bacteria?

A

coccus, rod, sporillum, filamentous, sporchete, Budding and appendaged bacteria (stalk and hypha)

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8
Q

Basic bacterial structures:

1) major
2) surface appendages
3) specialised structures

A

1) Major structures – cell wall, cell membrane, nucleoid/cytoplasm
2) Surface appendages – flagella, fimbriae, capsule
3) Specialised structures – spores, inclusion bodies

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9
Q

Whats the difference in cell wall of gram positive and gram negative bacteria?

A

gram positive bacteria- have a thick peptidoglycan layer ( retains crystal violet better), but 1 plasma membrane
gram negative bacteria have a rela. thin peptidoglycan layer but 2 plasma membranes , also therefore has a periplasm

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10
Q

Descbide the stages of gram staining:

A

STAINING

  1. Flood the heat-fixed smear with crystal violet for 1 min
  2. Add iodine solution for 1 min
  3. Decolorize with alcohol briefly- 20sec
  4. Gram-positive bacteria will turn purple ( as they have a thick peptidoglycan layer that retains crystal violet stain after washing with alcohol
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11
Q

What is the principle of gram-staining?

A

negatives have a 2nd membrane, its asymmetric and its outer core is lipopolysaccharide. The staining differentiates based on the fact that the peptidoglycan is thick and uncovered in gram positive so retains crystal violet-iodide complex but thin and covered in gram negative so is permeable to the complex.

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12
Q

Streptococcus pyogenes:

1) Where is it carried?
2) What does an acute infection cause?
3) How is it spread?
4) What is the incubation period
5) What does it cause?

A

1) respiraotry tract
2) pharyngitis (severe sore throat)
3) spread by droplets of saliva or nasal secretions
4) 2-4 day
5) o Pharyngitis, tonsillitis, malaise, fever, headache, redness, lymph node enlargement in throat

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13
Q

1) Give an example of gram +ve cocci?

2) Give an example of gram -ve rods?

A

1) Streptococcus pyogenes

2) Salmonella entrica

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14
Q

Salmonella entrica

1) What is the source of infection?
2) What is its most common form and how long does it last?
3) Give an example of a dangerous form?

A

1) foodborne infections
2) Most common form is enterocolitis lasting 2-5 days
3) S.enterica serovar Typhi (typhoid fever)

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15
Q

Which bacteria (+/-ve) is easier to treat with antibiotic?

A

+ve

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16
Q

1) What is the outer membrane of gram -ve bacteria composed of?2) What anchors the outer membrane to to peptidoglycan layer?

A

1) LPS (lipopolysaccharide)

2) Braun’s lipoproteins

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17
Q

What are fimbria?

A

protein filamentous structures, enable cells to stick to surfaces, aid biofilm production

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18
Q

pili?

1) they are similiar to…
2) 2x purpose:
3) 2x e.g.
4) What is the function of type 4 pili?

A

1) similar to fimbriae (longer, fewer on cell), 2)genetic exchange (conjugation), adhesion of pathogens to host cells,
3) e.g. Neisseria spp, S.pyogenes,
4) type 4 pili allow twitiching motility,

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19
Q

Endospores:

1) can all bacteria form them?
2) Spores are resistant, how do we kill them?
3) give 2 e.g.s of spore producing bacteria:
4) what state is the cell in before releasing spore?

A

1) no, only some
2) kill by autoclave
3) Bacillus anthracis, Clostridium difficile
4) vegetative ( it is starving)

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20
Q

Capsules and slime layers:
1) made up of..
2) describe structural strength:
3) capsules are adhered to ____a___ by ___b___
4) compare deformation property of capsule and slime layer
5) Polysaccharides – aid adhesion (biofilm), evade phagocytosis, protect against desiccation
• Help maintain ideal pH for them in the mouth

A

1) Polysaccharide or protein
2) No structural strength
3) a) cell b)tight matrix,
4) Slime layer = more easily deformed

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21
Q

What are cell inclusions made out of?

A 
Inclusions are dense aggregates of specific chemical compounds in the cell. LIKE: 
Carbon storage polymers:
1. Poly –β-hydroxybutyric acid (lipid)
2. Glycogen (Streptococcus mutans
intracellular polysaccharide)
3. polyphosphate
4. Sulphur
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22
Q

What are the purposes of cell inclusion bodys?

Why are they used?

A

• Packets of energy reserves or building
blocks
• Safe way to store (osmotic stress)

23
Q

Growing bacteria - nutrition and culture:
To grow must produce and consume energy –1) What type of reactions will be occurring?
2) What is needed?
3) How do they control metabolism of these substances?
4) What % of water is there in bacteria?

A

1) Anabolic and catabolic
2) a) Need nutrients (food) – macro/micro nutrients
b) Needs vary, though hydrogen, oxygen, carbon, nitrogen, phosphorus, sulphur and selenium pivotal
3) They control metabolism of these substances through regulatory mechanisms e.g. transcriptional control
4) 70-80% water

24
Q

Where do the following obtain carbon?

1) Heterotrophs
2) Autotrophs

A

1) Heterotrophs – obtain carbon from organic chemicals , these are the ones we deal with.
2) Autotrophs – obtain carbon from CO2

25
Q

1) What is the first reaction of fermentation and respiration?

A

• With glucose as substrate, glycolysis is the first step in both pathways

26
Q

Describe respiration

A

electron donor is oxidised with O2 or O2 substitute

27
Q

Describe fermentation:

A

organic compound used as both electron donor and electron acceptor takes glucose and makes pyruvate while recycling the NADH

28
Q

Descibe function/role of ATP in

1) fermentation
2) respiration

A

1) In fermentation, ATP is synthesized by substrate-level phosphorylation
2) In respiration, oxidative phosphorylation drives ATP synthesis

29
Q

What synthesises ATP in bacteria:

2) Where is it and what is it?
3) How many H+ are needed to flow in/out of the cell to produce one ATP?
4) do they flow in or out?

A

F0F1 ATPase

2) Highly abundant protein complex in actively growing bacterial cell walls
3) 3
4) in

30
Q

Other than the production of ATP what else is ATPase used for (e.g.A.mutans)?

A

ATPase to pump H+ out of cells so that when we eat sugar= high amount of acid, they use energy to get acid out of cell.

31
Q

Explain the Acid-fast staining procedure:

A
  1. Add carbol fuchsin stain to a heat fixed smear then heat.
  2. Wash
  3. Add 3% acid alcohol to decolorize (all bacteria are red until this is added, it decolorizes the non acid-fast bacteria)
  4. Wash
  5. Add counterstain (methylene blue: turns non acid-fast bacteria that have been decolorized blue)
32
Q

Describe structure and composition of acid-fast bacteria:

A
  1. Outer membrane
  2. Layer of arabinogalactan (adds strength to cell wall-joins outer membrane and peptidoglycan layer)
  3. thin layer of peptidoglycan- prevents osmotic lysis

The outer membrane is composed of surface proteins, porins and most importantly to the staining process mycolic acids and other glycolipids.

33
Q

1) Why does 3% alcohol not decolorise acid-fast bacteria in the acid-fast staining process?
2) Give an example of a clinically relevant acid-fast bacteria:

A

1) Due to the mycolic acids It has a high lipid/wax content. This is important in the entry and exclusion of molecules (e.g. alcohol) so like gram negative requires transporters for small hydrophilic molecules therefore alcohol can not penetrate bacterium to decolorise the carbol fuchsin
2) e.g. Mycobacterium tuberculosis (TB)

34
Q

What 3 ways to culture media vary:

A

1) Defined versus complex (can embellish)
• Can be selective or differential/indicator (especially diagnostics)
• Vastly different nutritional requirements

35
Q

What are micro- and macro- nutrients?

A

Micronutrients, as opposed to macronutrients (protein, carbohydrates and fat), are comprised of vitamins and minerals which are required in small quantities to ensure normal metabolism, growth and physical well-being.

36
Q

Would heterotrophic organisms grow well in inorganic salt media? Why or why not?

A

Heterotrophic organisms require organic compounds for their energy source and their carbon source. Without any organic molecules in the media, the bacteria will have nothing for energy or a carbon source. Therefore, the bacteria will not grow in this media.

37
Q

Why is complex media generally used to cultivate microorganisms?

A

Complex media has lots of nutrients (amino acids, sugars, vitamins and minerals) which would be required for growth of most microorganisms. For most microbes, this is enough for growth.

38
Q

Is blood agar
1) selective or differential/indicator
2) defined or complex
growth medium…

A

blood agar: differential because it is used to distinguish pathogenic bacteria based on the effect of bacterial enzymes known as hemolysins which lyse red blood cells, Complex media

39
Q

1) What is the name given to bacterium cell division?
2) growth drawn onto a graph is…
3) What are the 3 ways growth is measured?

A

1) binary fission
2) exponential
3) • Microscopic counts
• Viable counts
• Turbidimetric methods

40
Q

How are autotrophs different to auxotrophs?

A

Auxotrophs, which
cannot synthesise an essential
organic compound (e.g. amino acid,
nucleotide etc).

41
Q

What is an hetetroph

A

obtain carbon from organic chemicals , these are the ones we deal with.

42
Q

What is an autotroph

A

an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. obtain carbon from CO2

43
Q

What is an auxotroph

A

a mutant organism (especially a bacterium or fungus) that requires a particular additional nutrient which the normal strain does not.

44
Q

Define bacterial growth

A

Irreversible increase in biomass

and also, usually, numbers

45
Q

What are the stages of a batch culture?

A

lag, exponential , stationary, death

46
Q

Describe changes in 1) turbidity and 2) viable count through the following stages:

a) lag,
b) exponential ,
c) stationary,
d) death

A

a) 1) rises expoentially
2) basicaly 0
b) 1) rises 2) also rises but lages behind turbidity
c) 1) flat lines
2) rises above turbidity then flat lines
d) 1) falls
2) falls more rapidly.

47
Q

How does Turbidimetric methods (optical density) of measuring bacterial growth work?

A

Photocell measures unscattered light, light will be scattered by bacteria. Recorder gives optical density or klett units.

48
Q

Give the stages of spread-plate mthod of a viable count of bacteria:

A

Spread-plate method

a) Serial dilution of the sample (bacteria) in sterile water and cultivating these on nutrient agar in a dish that is sealed and incubated.
b) Colonies counted by eye.

49
Q

Why are serial dilutions used?

A

As you want to be counting as many colonies as possibles to make results more significant but too many colonies and then they overlap.

50
Q

When is the pour plate method used?

A

When analysing a bacterial species that grows poorly in air.

51
Q

How does the pour plate method differ from the spread-plate method?

A

So step one instead of spreading, you mix your diluted bacterial sample with melted agar and then that mixture is poured into a petri dish.

52
Q

Describe the process of a microscopic count?

A

a) Sample added slide and coverslip placed on top so that space between coverslip and slide is no greater than 0.02mm (1/50mm) . ( Overflow must be avoided as you are adding a known volume to slide, and overflow would lead to loss of bacteria and a false result)
b) Count the number of bacteria in one of the 25 squares which have a total area of 1mm2 and thus a total volume of 0.02mm3.
c) quick math

53
Q

Why must overflow be avoided when carrying out a microscopic count of bacterial population:

A

Overflow must be avoided as you are adding a known volume to slide, and overflow would lead to loss of bacteria and a false result

Stage 2 Microbiology for dentists (25 decks)

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