Infectious Diseases - Pneumococcus, Streptococcus and Staphylococcus

Question 1

What do pneumococcal bacteria look like under the microscope?

Answer 1

Gram + streptococcus (alpha-haemolytic)
Grow in chains or pairs
Encapsulated

Question 2

What are the virulence factors of pneumococcal infections?

Answer 2

Pneumolysin (cytotoxin)

LytA (enhances pathogenesis)

Pneumococcal H inhibitor (HiC) inhibits C3 convertase synthesis

Pneumococcal surface protein C (PspC) binds factor H to breakdown C3

Question 3

What are the adherence factors of pneumococcal infections?

Answer 3

Neuraminidase NanA

Pneumococcal surface adhesion A (PsaA)

Question 4

What are the risk factors for pneumococcal infection?

Answer 4

Asplenia/splenic dysfunction
Chronic respiratory/heart/liver/kidney disease
Diabetes mellitus
Immunosuppression
Cochlear implants

Question 5

How many people with pneumococcal pneumonia get a positive blood culture?

Answer 5

<30%

Question 6

What kind of pneumonia does pneumococcal pneumonia cause?

Answer 6

Lobar or segmental consolidation

Question 7

What diagnostic test has a HIGH predictive value for pneumococcal pneumonia?

Answer 7

Pneumococcal urinary antigen

Question 8

What serum investigations have associated with HIGH MORTALITY in pneumococcal infections?

Answer 8

Leukopenia

Question 9

How common is empyema in pneumococcal pneumonia?

Answer 9

In <5%

Question 10

What clinical infections are caused by pneumococcal?

Answer 10

Pneumococcal pneumonia
Meningitis (with 20% mortality)
Sinusitis/Otitis media

Question 11

What do straphylococcus look like under the microscope?

Answer 11

Gram positive catalase positive cocci

Question 12

How does staphylococcus evade and cause problems?

Answer 12

Commonly induces abscess formation

Interferes with neutrophil migration:

• chemotaxis inhibitory protein (CHIP)
• extracellular adherence protein

Question 13

What are the toxin mediated diseases caused by staphylococci and how do they develop?

Answer 13

Enterotoxin and Toxic Schock Syndrome Toxin 1 (TSST-1)

Result in overexpansion of T cells –> CYTOKINE STORM
–> IFNgamma, IL1, IL6, TNFalpha, TNFbeta

The preformed enterotoxin also stimulates the vagus nerve in food poisoning

Question 14

What is the importance of the exfoliative toxins that can be produced by staphylococci?

Answer 14

Exfoliative toxins ETA and ETB result in staph scalded skin syndrome

Question 15

What clinical presentations are caused by staphylococcus?

Answer 15

• Skin and soft tissue infections
• Musculoskeletal:
• -> vertebral osteomyelitis (RF: dialysis, endocarditis, diabetes and IVDU)
• -> epidural abscess
• -> septic arthritis (esp knee, shoulder, hip and finger)
• Respiratory infection
• -> CXR has ‘shaggy’ and thin walled cavities, usually following viral flu
• bacteraemia
• endocarditis

Question 16

What clinical presentations are caused by coagulase-negative staphylococcus?

Answer 16

Staph epidermidis: device infections

Staph saphrophyticus: UTIs in young women

Question 17

What do STREPTOCOCCUS look like under the microscope?

Answer 17

Gram positive cocci growing in chains

Question 18

What are the Group A (beta haemolytic) strep and what particular virulence factors?

Answer 18

Strep pyogenes

Have M protein and are encapsulated

Question 19

What are the Group C and G strep?

Answer 19

S millerai, S intermedius and S anguinous

Question 20

Which group of strep is associated with peri-partum fevers?

Answer 20

S agalactiae (Group B)

Question 21

What group of strep is associated with neoplasm of the GI tract?

Answer 21

Group D S bovis

Question 22

What clinical presentations are caused by Streptococcus?

Answer 22

• pharyngitis
• -> post infective acute renal failure
• -> post infective acute post-strep GN
• Scarlet fever
• -> assoc: strawberry tongue, sandpaper skin and Pastia’s lines (=rash in skinfold) followed by desquamation of palms and soles
• Skin:
• -> IMPETIGO (nonpainful and afebrile honeycombing crust on mouth, nose and legs)
• -> CELLULITIS
• -> NECROTISING FASCIITIS
• Pneumonia and empyema