CSIM 1.41 Case 42 Round Up - Epiglottitis. Staphs and Streps

Question 1

What are the main organisms causing upper respiratory tract infections? (FROM HIGHEST UP IN RESP. TRACT TO LOWEST)

Answer 1

• Staphylococcus aureus
  
  • Neisseria meningitidis
  • Streptococcus pyogenes
  • Corynebacterium diphtheriae
  • Haemophilus influenzae

Question 2

Describe Staph aureus:

1) Gram positive or negative
2) Catalase
3) Aerobicity
4) salt tolerance
5) Haemolysis

Answer 2

1) Gram positive
2) Catalase positive
3) faculatative anaerobes
4) tolerant - up to 10%
5) Beta-haemolytic

Question 3

Describe Neisseria meningitidis:

1) Structure
2) Gram
3) C

Answer 3

1) Diplococcus

2) Gram negative

Question 4

Describe what makes Neisseria meningitidis particularly virulent when it enters the blood

Answer 4

• Continuous production of outer membrane leads to endotoxin-induced toxic shock
  
  • Capsule protects agains phagocytosis

Question 5

Describe the properties of streptococcus pyogenes and streptococcus pneumoniae

1) Gram
2) Catalase
3) Haemolysis

Answer 5

S. pyogenes
• Gram positive
• Catalase negative
• Beta-haemolytic

S. pneumoniae
• Gram positive
• Catalase negative
• Alpha-haemolytic

Question 6

Describe Corynebacterium diphtheriae

1) Gram
2) Shape

Answer 6

• Gram-positive

* Rods (form ‘chinese letters’)

Question 7

What does Corynebacterium diphtheriae cause?

Answer 7

Diphtheria
• Produces diphtheria EXOtoxin which causes fever and heart failure
• Adheres to the tonsils and pharynx by producing a pseudomembrane
• Spreads upwards and downwards leading to respiratory obstruction

Question 8

Describe haemophilus influenzae

1) Gram
2) Shape
3) Aerobicity

Answer 8

• Gram-negative
  
  • Coccobacilli
  • Facultative anaerobe

Question 9

What are the main organisms causing lower respiratory tract infections?

Answer 9

• Coccidioides immitis
  
  • Bordetella pertussis
  • Chlamydia psittaci
  • Mycobacterium tuberculosis

Question 10

Which bacteria causes whooping cough?

What are the features of this bacterium?

1) aerobic or anaerobic
2) gram
3) shape
4) toxic products

Answer 10

Bordetella pertussis
  •  Anaerobic
  •  Gram negative
  •  Rods
  •  Produces pertussis endotoxin

Question 11

How does bordatella pertussis bind to the lower respiratory tract?

Answer 11

Filamentous haemoaglutinin adhesin binds to sulphatides on cilia of epithelial cells

Question 12

Describe the features of Chlamydia psittaci
  •  Gram
  •  Haemolysis
  •  Oxygen metabolism
  •  Structure
  •  Catalase test

Answer 12

• Gram positive
  
  • Diplococcus
  • Alpha-haemolytic
  • Facultative anaerobe
  • Catalase negative

Question 13

What are the gram negative and gram positive genuses of pathogenic bacteria of the airways

Answer 13

Gram positive:
  •  Staphylococcus
  •  Streptococcus
  •  Corynebacterium 
  •  Chlamydia

Gram negative
• Haemophilus
• Bordatella
• Neisseria

Unclassified by gram staining:
• Mycobacterium

Question 14

Describe Mycobacterium tuberculosis
• Gram
• Shape

Answer 14

• No gram staining due to outer waxy lipid cell walls

* Rods

Question 15

Describe the virulence of Mycobacterium tuberculosis

Answer 15

No toxins produced, virulence relies on cell wall

Question 16

what does being catalase positive tell you about a bacterium?

Answer 16

that it has an oxidative metabolism

Question 17

how can you distingush between staphylococcus and streptococcus? What eatures do these share?

Answer 17

Catalase test:
• Staph = positive
• Steptococcus = negative

Morphology:
• Staph divides in all planes resulting in clusters of cells
• Streptococcus divides in a single plane perpendicular to the long axis of the well resulting in chains or pairs of cells
• IMG 107

Both gram positive
Both non motile
Both non-spore forming

Question 18

what does being catalase negative tell you about a bacterium?

Answer 18

that it has an fermentative metabolism and so produces lactic acid as a bi-product of normal metabolism

Question 19

What are the two types of Staphylococcus?

Answer 19

Coagulase positive
  •  Virulent
  •  converts fibrinogen to fibrin
  •  this creates a fibrin coat isolates the bacterium from phagocytic cells and other defences
  •  Causes blood clotting
  •  Clump and precipitate in test tubes

Coagulase negative
• Less virulent
• Remains suspended and turbid in test tubes

Question 20

Is staph aureus coagulase positive or negative?

Answer 20

Positive - more virulent

Question 21

What is methicillin-resistant staph aureus

Answer 21

MRSA

Staph aureus which is resistant to all beta-lactam antibiotics
• Produces coagulases causing blood clots
• Beta-haemolytic

Question 22

How is MRSA identified?

Answer 22

• Gram staining
  
  • Catalase test
  • Coagulase test
  • DNA fingerprinting

Question 23

What are the different groupings of streptococcus

Answer 23

Three broad groups based on blood agar:
• Alpha
• Beta
• Gamma

Serological groups
  •  A
  •  B 
  •  C
  •  ...

Question 24

What are the two most prevalent virulent species of streptococcus?

Answer 24

• S. pyogenes

* S. pneumoniae

Question 25

Describe the groups S. pyogenes belongs to

Answer 25

• Group A

* Beta - haemolytic

Question 26

What are the acute manifestations of S. pyogenes infections?

Answer 26

• Pharyngitis (sore throat)
  
  • Impetigo (IMG 108)
  • Scarlett fever (IMG 110)
  • Cellulitis (IMG 109)
  • Invasive toxigenic infections (necrotising fasciitis - IMG 111)

Question 27

How is streptococcus transmitted?

Answer 27

Through droplets

Question 28

Describe what happens in necrotising fasciitis

Answer 28

Destruction of the sheath covering skeletal muscle due to invasive infection of subcutaneous tissue - IMG 111

Question 29

Why does S. pneumoniae grow particularly well in lungs?

What sputum does this bacterium produce?

Answer 29

It is a facultative anaerobe and its growth is enhanced by 5-10% CO2

Rust-coloured