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Medical Microbiology > 3 Bacteriology > Flashcards

3 Bacteriology Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What are the characteristics of bacteria?

A
  • Microscopic organisms
  • PROkaryotes
  • Lack a true nucleus
  • Generally have one chromosome
  • DO NOT all look the same
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2
Q

How can bacteria appear?

A

Cocci (spherical shaped)
Rods (elongated and cylindrical)- straight, curved and spiral
Filamentous

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3
Q

What are the dimensions of bacteria?

A

Vary by species- generally about 2-3um long and 1.0 um in diameter

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4
Q

How can bacteria be visualised?

A

Colony form however it is necessary to use microscopy (light microscope or electron microscope)

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5
Q

Benefits of using light microscopy.

A

Easy to use and provided in most labs

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6
Q

What does oil immersion do?

A

Allows for a sharp image at the high magnification of x1000

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7
Q

What does the use of dyes to view bacteria rely on?

A

Cationic organic compounds combining with the negatively charged cell envelope

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8
Q

What steps are involved in the Gram staining process?

A

Bacteria is stained with Crystal Violet, then iodine (at this point Gram negative becomes decolourised), then counterstain with Safranin

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9
Q

How do you tell the difference between Gram-positive and Gram-negative?

A

Gram-positive is purple

Gram-negative is pink

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10
Q

What else can Gram staining be used for?

A

Can be used as a rough approach to check for contamination of bacterial cultures

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11
Q

Are bacteria unicellular or multicellular?

A

Unicellular

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12
Q

Why do bacteria have cell walls?

A

Solutes dissolved in the cytoplasm generate osmotic pressure, this pressure would be enough to rupture the cells

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13
Q

What do the bacterial cells walls do?

A

Gives the cell strength and rigidity and influences the cells shape

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14
Q

What is another name for peptidoglycan?

A

Murein

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15
Q

What is peptidoglycan composed of?

A

Two glucose derivatives (NAG and NAM/NAMA) and amino acids (normally 4 but ranges from 3-5

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16
Q

What does NAG stand for? And what is its formula?

A

N-acetylglucosamine

C8H15NO6

17
Q

What does NAM or NAMA stand for? And what is its formula?

A

N-acetylmuramic acid

C11H19NO8

18
Q

Name some amino acids that compose peptidoglycan.

A

L- and D- Alanine, D-glutamic acid, Diaminopimelic acid (DAP)/lysine

19
Q

What do the components of peptidoglycan exist as? And what are they called?

A

A repeating structure

Glycan tetrapeptides

20
Q

What is the difference between the thickness of Gram-positive and Gram-negative walls?

A

Gram positive ~ 20-80nm thick

Gram negative ~ 7-8nm thick

21
Q

What is the composition of the Gram-positive cells wall?

A

~90% peptidoglycan

This includes techoic acids

22
Q

What is the composition of the Gram-negative cell wall?

A

~5-20% peptidoglycan
LACK techoic acids
There is an additional membrane layer present

23
Q

What is the additional layer present in a Gram-negative cell?

A

Lipopolysaccharide layer - exists as a lipid bilayer

Surrounds the peptidoglycan and cytoplasmic membrane

24
Q

What does the Lipopolysaccharide layer contain?

A

Proteins, many of which are transmembrane

25
Q

Lipids within the lipopolysaccharide layer are what?

A

Highly glycosylated

26
Q

What else is the LPS known as?

A

Endotoxin

27
Q

What sort of response does endotoxin have the potential to raise?

A

Immune - causes a fever (Endotixin is pyrogenic)

28
Q

What do some bacterial species produce?

A

Endospores

29
Q

What are endospores resistant to? And what does this mean?

A

Heat and many antimicrobials also highly resistant to UV radiation, gamma radiation etc

They can persist in an environment for long periods of time

30
Q

Endospores have a highly complex structure consisting of how many layers? And what are the layers?

A

4

Outermost layer - exosporium
Next layer inwards - Spore coat (made from peptidoglycan)
Next layer inwards - cortex (rich in proteins)
Inner area - Core, contains protoplasm, bacterial DNA and enzymes for cell replication

31
Q

What is the core rich in?

Hint: it helps with survival.

A

Pyridine 2,6 dicarboxylic acid/calcium ion complex

32
Q

How is the staining of endospores carried out?

A

Schaffer-Fulton staining using malachite green

Medical Microbiology (9 decks)

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