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Phase 2 Medicine > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is a pathogen?

A

Organism that causes or is capable of causing disease.

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2
Q

What is a commensal?

A

Organism that colonises host but causes no symptoms in normal conditions.

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3
Q

What is virulence/pathogenicity?

A

Degree to which organism is pathogenic

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4
Q

What is asymptomatic carriage?

A

Pathogen is carried harmlessly at tissue site where it causes no disease.

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5
Q

What colour do gram positive bacteria stain?

A

Purple

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6
Q

What colour do gram negative bacteria stain?

A

Pink

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7
Q

What are the two main shapes of bacteria?

A

Round (Cocci), or rod-shaped (Bacilli)

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8
Q

How can cocci look under a microscope?

A

Diplococcus (two cocci)
Chains of cocci
Clusters of cocci

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9
Q

How can bacilli look under a microscope?

A

Chain of bacilli
Vibrio (curved bacilli)
Spirochaetes (spiral rod)

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10
Q

Which areas of the body can be colonised by bacteria?

A

Mucosal surfaces

  1. Mouth
  2. Skin
  3. GI tract
  4. End of the urethra
  5. Vagina
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11
Q

Which areas of the body are sterile?

A
  1. Lungs
  2. Gallbladder
  3. Kidneys
  4. Ureters
  5. Bladder
  6. First part (most) of the urethra
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12
Q

What is the form of genetic material that bacteria carry?

How is this translated to protein?

A

Single chromosome of double stranded DNA.

DNA>RNA>Protein using ribosomes

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13
Q

How many cell membranes do gram positive bacteria have?

A

1 cell membrane

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14
Q

How many cell membranes do gram negative bacteria have?

A

2 cell membranes

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15
Q

What are pili?

A

Pili are projections on the outside of some bacteria that allow them to attach to the host

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16
Q

How is having a polysaccharide capsule beneficial to bacteria?

A
  1. Prevents desiccation
  2. Protects from immune system (protects from the complement system).
    - Immune system cannot recognise certain carbohydrates
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17
Q

What are flagella?

A

Flagella are long/wavy projections that allow motility.

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18
Q

What are the outer components of gram positive bacteria?

A

Cytoplasmic membrane linked to a large layer of peptidoglycan by lipoteichoic acid.

In some cases there is a capsular layer on top of the peptidoglycan.

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19
Q

What are the outer components of gram negative bacteria?

A

There are two cytoplasmic membranes. In between the membranes, there is an area called the periplasmic space.
Inside the periplasmic space is a thin layer of peptidoglycan.
On the outer membrane is a layer of lipopolysaccharide which is linked to the outer membrane with lipid A.
The lipopolysaccharide is also known as endotoxin.
Endotoxins are very easily recognised by the immune system and can trigger septic shock.
The lipopolysaccharide layer may be covered in a capsular layer.

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20
Q

What is the range of temperatures that bacteria can colonise?

A

Bacteria can live at 80 deg Celsius. Spores can survive to 120 degrees.

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21
Q

What pHs can bacteria survive at?

A

<4-9

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22
Q

Can bacteria survive desiccation? Can they survive UV light?

A

Some bacteria can survive desiccation and some spores can survive this for >50 years.
Some bacteria can survive UV radiation.

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23
Q

How long does it take for Mycobacterium Tuberculosis to double in number? What about Mycobacterium leprae?

A

TB - 24 hours

Leprosy - 2 weeks

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24
Q

What is the lag phase?

A

Bacteria get used to the new environment.

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25
Q

What comes after lag phase?

A

Exponential/log phase where bacterial number increases exponentially

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26
Q

What is the stationary phase?

A

Bacteria begin running out of nutrients.

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27
Q

What is the death phase?

A

Number of viable bacteria decrease.

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28
Q

What is endotoxin?

A

Component of outer membrane of gram negative bacteria.

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29
Q

What are exotoxins?

A

Proteins secreted by both gram positive and negative bacteria that are able to cause damage to the host.

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30
Q

What are the features of endotoxin?

A
  • Made of lipopolysaccharide
  • Non-specific
  • Heat will not affect the action of lipopolysaccharide
  • Weak antigenicity
  • Cannot be converted to toxoid
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31
Q

What are the features of exotoxin?

A
  • Made of protein
  • Specific as they are proteins
  • Heat will damage the exotoxins and denature them.
  • Strong antigenicity
  • Can be converted to toxoid
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32
Q

How and why are toxins converted into toxoids?

A

Converted using formaldehyde so that they lose their toxicity but retain antigenicity. They can then be used for innoculation/vaccination against the toxin.

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33
Q

List 6 things that cause genetic variation in bacteria.

A
  1. Base substitution
  2. Deletion
  3. Insertion
  4. Transformation via plasmid
  5. Transduction via bacteriophages
  6. Conjugation via sex pilus
34
Q

What are obligate intracellular bacteria?

A

Bacteria that can only be cultured in tissue (eg. chlamydia)

35
Q

Name a type of bacteria that can be cultured on artificial media that does not have a cell wall.

A

Mycoplasma

36
Q

Name a type of bacteria that can be cultured on artificial media that has a cell wall and grows as filaments

A

Actinomyces - causes actinomycosis (slow-growing face infection)

37
Q

Which type of bacteria can cause osteomyelitis?

A

Staphylococcus Aureus

38
Q

What is coagulase and how does it help protect bacteria?

A

Enzyme produced by bacteria that coats the outside of the bacteria and clots blood plasma (forms fibrin clots)
These clots protect the bacteria from phagocytosis.

39
Q

How is the coagulase test used in classification of Staphylococcus?

A

Staphylococcus Aureus = coagulase positive

Other Staphylococcus Spp. = coagulase negative

40
Q

Are coagulase negative bacteria involved in opportunistic infections?

A

Yes

41
Q

Give an example of coagulase negative bacteria.

A

Staph. Epidermidis

42
Q

Where does S. Aureus usually reside?

A

Present on skin and nose of 30% of population

43
Q

How is S. Aureus spread?

A

Aerosol and touch

44
Q

Which antibiotics is MRSA resistant to?

A
  • β lactams
  • Gentamycin
  • Erythromycin
  • Tetracycline
45
Q

Which gene transfers resistance to MRSA?

A

MecA gene

46
Q

What are the 4 types of virulence factors that S. Aureus has?

A
  • Pore-forming toxins
  • Toxic Shock Syndrome Toxin (TSST)
  • Protein A
  • Proteases
47
Q

What are the two main pore-forming toxins used by S. Aureus?

A
  • α-haemolysin

- Panton Valentine Leucocidin (PVL)

48
Q

How does Toxic Shock Syndrome Toxin work?

A

TSST is a supertoxin which triggers cytokine release. This huge inflammatory reaction to TSST causes Toxic Shock Syndrome.

49
Q

How does Protein A work?

A

Protein A is a protein on the surface of S. Aureus that causes Ig to bind in the wrong direction. This prevents the immune response from working properly.

50
Q

How do proteases secreted by S. Aureus work?

A

S. Aureus secretes proteases such as exfoliatin which attacks and digests the proteins in desmosomes between skin cells. This causes the skin to peel away.
This results in a condition called scalded skin syndrome which usually affects children.

51
Q

List 7 associated pyogenic conditions of S. Aureus.

A
  • Wound infections (cellulitis)
  • Abcesses
  • Impetigo
  • Osteomyelitis
  • Septicaemia
  • Pneumonia
  • Endocarditis
52
Q

List 3 associated toxin-mediated conditions of S. Aureus.

A
  • Toxic Shock Syndrome
  • Scalded Skin Syndrome
  • Food poisoning
53
Q

List 3 conditions associated with coagulase negative infections.

A
  1. Infected implants
  2. Septicaemia
  3. Endocarditis
54
Q

Give two examples of coagulase negative bacteria.

A

S. Epidermidis

S. Saprophyticus

55
Q

Who/what does S. Epidermidis infect? What is its main virulence factor?

A

S. Epidermidis is opportunistic so usually infects the debilitated. Usually infects indwelling catheters and prostheses.
Its main virulence factor is its ability to form biofilms

56
Q

What does S. Saprophyticus cause?

A

Acute cystitis

57
Q

Which protein produced by S. Saprophyticus allows it to bind to human cells?

A

Haemagglutinin allows it to adhere to human cells.

58
Q

Which protein produced by S. Saprophyticus causes kidney stones?

A

Urease causes the urine to become alkaline which causes kidney stones.

59
Q

How can you distinguish between Staphylococcus and Streptococcus down a microscope?

A

Staphylococcus - clusters

Streptococcus - chains

60
Q

What are the 3 ways of classifying Streptococci?

A
  1. Haemolysis
  2. Lancefield grouping
  3. Biochemical properties
61
Q

What are the three types of haemolysis and how do they look on an agar plate?

A

α - partial haemolysis (green)
β - full haemolysis (clear area on agar)
γ - no haemolysis

62
Q

What is Lancefield typing?

A

Method of grouping coagulase negative bacteria according based on bacterial carbohydrate cell surface antigens. (A-H and K-V)

63
Q

Briefly describe the Lancefield test.

A

Add the bacteria to a different antiserum for each group. Clumping indicates a positive reaction.

64
Q

Which Lancefield groups do most pathogenic Streptococci belong to?

A

A and B.

65
Q

Give an example of a Lancefield group A strep?

A

S. Pyogenes

66
Q

Give an example of a Lancefield group B strep?

A

S. Agalactiae

67
Q

What are the infections that can be caused by S. Pyogenes?

A
  • Cellulitis
  • Tonsillitis
  • Otitis Media
  • Impetigo
  • Scarlet fever
68
Q

What are the possible complications of an S. Pyogenes?

A
  1. Rheumatic fever

2. Glomerulonephritis

69
Q

What is rheumatic fever?

A

Inflammatory disease of the heart, joints, skin and brain

70
Q

How do we assess the risk of further complications of S. Pyogenes?

A

Anti-Streptolysin O Test. This is an agglutination reacton. >200IU/ml=agglutination

71
Q

What are the two main surface factors on S. Pyogenes? How do they aid the bacterium?

A
  1. M protein - encourages complement degradation

2. Capsule - contains hyaluronic acid which protects against phagocytosis

72
Q

What are the exported factors of S. Pyogenes?

A

Enzymes and toxins.

73
Q

What are the three main enzymes used by S. Pyogenes in infections?

A
  1. Hyaluronidase - used for spreading
  2. Streptokinase - breaks down clots
  3. C5a peptidase - breaks down complement and reduces chemotaxis
74
Q

What are the two main toxins used by S. Pyogenes in infections?

A

Streptolysins O and S - break down red blood cells and bind to cholesterol so they can bind to host cells
Erythrogenic toxins - stimulate an exaggerated host response (similar to Toxic Shock Syndrome Toxin)

75
Q

What is rust-coloured sputum a sign of?

A

Streptococcal Pneumoniae

76
Q

What are draughtsman colonies indicative of?

A

Strep. Pneumoniae

77
Q

What can a Strep. Pneumoniae infection cause?

A
  1. Pneumococcal Pneumonia
  2. Otitis Media
  3. Sinusitis
  4. Meningitis
78
Q

What factors disposes you to Strep. Pneumoniae?

A
  1. Impaired mucous trapping (due to viral infection)
  2. Hypogammaglobulinaemia
  3. Asplenia
79
Q

What is hypogammaglobulinaemia?

A

Hypogammaglobulinaemia occurs when serum immunoglobulin levels are reduced.

80
Q

What are the three virulence factors of Strep. Pneumoniae?

A
  1. Capsule - can be made of 84 different types of polysaccharide, is antiphagocytic
  2. Inflammatory wall constituents

Phase 2 Medicine (10 decks)

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