MCD - microbiology > Bacterial properties > Flashcards

Bacterial properties Flashcards

(25 cards)

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1
Q

Describe the basic structure of bacteria

A
  • Small and unicellular
  • No internal organelles (no chloroplasts, mitochondria)
  • Haploid
  • Some have flagella
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2
Q

Name the different shapes of bacteria

A
  • Cocci
  • Bacilli
  • Spirilli
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3
Q

What is the difference between Gram-positive and Gram-negative bacteria?

A

POSITIVE:

  • Thick peptidoglycan layer (retains violet dye well = deep violet stain)
  • One membrane (cytoplasmic)

NEGATIVE:

  • Thin peptidoglycan layer (violet dye is lost = cells absorb counterstain = appear pink)
  • Two membranes (cytoplasmic and outer membranes)
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4
Q

Where is peptidoglycan found in gram+ and gram- bacteria?

A

POSITIVE = cell wall

NEGATIVE = in periplasm (area between the two membranes)

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5
Q

What feature is found only on Gram-negative cell walls?

A
  • Lipopolysaccharide
  • Found in outer membrane
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6
Q

Give examples of some Gram + and - pathogenic bacteria and the diseases they cause.

A

POSITIVE:

  • Staphylococcus aureus (skin diseases, endocarditis, pneumonia)
  • Streptococcus pneumoniae (pneumonia, meningitis)
  • Streptococcus pyogenes (tonsillitis, scarlet fever)

NEGATIVE:

  • Escherichia coli (EPEC - diarrhoea, EHEC - produces toxin, dysentery and kidney failure)
  • Shigella (dysentery)
  • Neisseria (meningitidis - meningitis, gonorrhoeae - gonorrhoea)
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7
Q

Give examples of some Mycobacteria and the diseases they cause

A
  • Mycobacterium tuberculosis (TB)
  • Mycobacterium leprae (leprosy)

NOTE: mycobacteria are neither gram+ or gram- (have a waxy cell wall)

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8
Q

What do bacterial pathogens do?

A
  • Colonise
  • Persist
  • Replicate
  • Disseminate within cells, tissues between organs and hosts
  • Cause disease (dysregulate immune responses)
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9
Q

Apart from gram+ and gram-, what is another way of classifying bacteria?

A

Intracellular and extracellular pathogens

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10
Q

Give examples of some extracellular pathogens

A
  • Staphylococcus
  • Streptococcus
  • Neisseria
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11
Q

Give examples of some intracellular pathogens

A
  • Listeria
  • Shigella
  • Salmonella
  • Mycobacteria
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12
Q

What are the three methods by which bacteria survive in the host cell?

A
  • Escape
  • Prevent fusion with lysosomes
  • Survive in phagolysosome
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13
Q

Salmonella is an actively invading bacteria. Describe how it invades cells (which are not naturally phagocytic) by motility and invasion

A

Two structures: flagellum and injectisome

FLAGELLUM:

  • Generates proton-motive force for movement

INJECTISOME:

  • Transfers virulence proteins into host cells
  • Causes actin polymerisation, membrane ruffling, bacterial internalisation
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14
Q

Describe another way in which actin is manipulated by bacteria

A
  • Bacteria (such as listeria and shigella) can polymerise actin at one pole of the bacterium forming comet tails
  • This polymerisation propels the bacterium through the cytoplasm
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15
Q

What are the 3 basic mechanisms for horizontal gene transfer (HGT)?

A
  • Transformation
  • Conjugation
  • Transduction
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16
Q

Explain the mechanism of transformation in HGT

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A

The uptake of naked DNA from the environment

E.g. Neisseria, Streptococcus

17
Q

Explain the mechanism of conjugation in HGT

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A

Transfer of genetic material in the form of a plasmid via a conjugation tube

18
Q

Explain the mechanism of transduction in HGT

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A
  • Bacteriophages infect a bacterium and take up some of the bacterial DNA
  • The bacteriophage then carries the bacterial DNA to another bacterium
19
Q

What is a Pathogenicity Island?

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A

Horizontally acquired genes that contribute to the virulence

20
Q

Where do gram+ bacteria retain a violet dye?

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A

In the peptidoglycan of their cell wall

21
Q

Why is the stain excluded from gram- bacteria?

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A

Excluded by the presence of an outer membrane

22
Q

What is an obligate intracellular pathogen?

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A

A pathogen that cannot be cultured freely on medium (e.g. Chlamydia)

23
Q

Variation in vertically transmitted DNA can occur as a result of…?

24
Q

What is acid-fast bacteria?

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A
  • Have a waxy substance called mycolic acid in their cell walls which makes them impermeable to many staining procedures (inc. Gram stain)
  • They are able to resist decolorisation with acid alcohol
25
What is peptidoglycan?
A polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall
MCD - microbiology
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