Infectious Diseases - Pneumococcus, Streptococcus and Staphylococcus Flashcards
What do pneumococcal bacteria look like under the microscope?
Gram + streptococcus (alpha-haemolytic)
Grow in chains or pairs
Encapsulated
What are the virulence factors of pneumococcal infections?
Pneumolysin (cytotoxin)
LytA (enhances pathogenesis)
Pneumococcal H inhibitor (HiC) inhibits C3 convertase synthesis
Pneumococcal surface protein C (PspC) binds factor H to breakdown C3
What are the adherence factors of pneumococcal infections?
Neuraminidase NanA
Pneumococcal surface adhesion A (PsaA)
What are the risk factors for pneumococcal infection?
Asplenia/splenic dysfunction Chronic respiratory/heart/liver/kidney disease Diabetes mellitus Immunosuppression Cochlear implants
How many people with pneumococcal pneumonia get a positive blood culture?
<30%
What kind of pneumonia does pneumococcal pneumonia cause?
Lobar or segmental consolidation
What diagnostic test has a HIGH predictive value for pneumococcal pneumonia?
Pneumococcal urinary antigen
What serum investigations have associated with HIGH MORTALITY in pneumococcal infections?
Leukopenia
How common is empyema in pneumococcal pneumonia?
In <5%
What clinical infections are caused by pneumococcal?
Pneumococcal pneumonia
Meningitis (with 20% mortality)
Sinusitis/Otitis media
What do straphylococcus look like under the microscope?
Gram positive catalase positive cocci
How does staphylococcus evade and cause problems?
Commonly induces abscess formation
Interferes with neutrophil migration:
- chemotaxis inhibitory protein (CHIP)
- extracellular adherence protein
What are the toxin mediated diseases caused by staphylococci and how do they develop?
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
What is the importance of the exfoliative toxins that can be produced by staphylococci?
Exfoliative toxins ETA and ETB result in staph scalded skin syndrome
What clinical presentations are caused by staphylococcus?
- 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
What clinical presentations are caused by coagulase-negative staphylococcus?
Staph epidermidis: device infections
Staph saphrophyticus: UTIs in young women
What do STREPTOCOCCUS look like under the microscope?
Gram positive cocci growing in chains
What are the Group A (beta haemolytic) strep and what particular virulence factors?
Strep pyogenes
Have M protein and are encapsulated
What are the Group C and G strep?
S millerai, S intermedius and S anguinous
Which group of strep is associated with peri-partum fevers?
S agalactiae (Group B)
What group of strep is associated with neoplasm of the GI tract?
Group D S bovis
What clinical presentations are caused by Streptococcus?
- 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
