VL16a: S.aureus pathogenicity

Question 1

What kinds of disease are caused by s.aureus?

Answer 1

• Bacteremia
• Infective endocarditis (in heart tissue and valves)
• Osteoarticular infections (bones and joints)
• Skin and soft tissue infections (incl connective tissue)
• Pleuropulmonary infections (thorax and lungs)
• Device related infections (catheters, implants)

Question 2

Name some characteristics of s.aureus (gram, where they live, tolerances)

Answer 2

30% of humans colonized (commensal)
gram positive
non-motile, facultative anaerobe
salt tolerant: survive on human skin
tolerant of desiccation: survive on environmental surfaces
optimum termperature 37°C
carried in nasopharync and on the skin
produce many virulence factors
no spores, no flagella
can produce capsules
aureus (golden) yellow on blood agar, often hemotlytic

Question 3

Name 2 other important species of staphylococci

Answer 3

S.epidermidis (opportunistic pathogen)
S.saprophyticus (causes UTI)

other gram + cocci include streptococci

Question 4

S.aureus and bacteremia

Answer 4

leading cause of bacteremia
risk increases for elderly, dialysis patients, drug users
often starts as skin infection that enters bloodstream through cut
even with anitbiotics 15-50% mortality
serious infection, staph regarded as common cause, bat outcome

Question 5

s.aureus and endocarditis

Answer 5

leading cause of endocarditis
risk increases for elerderly, patients with prosthetic valves
origins, intravenous catheters, prosthetic heart valves, inflammation associated with heart disease
outcome 22-66% mortality
management: antibiotics and surgery

Question 6

jhg

Answer 6

SCV small colonie variants

Question 7

What skin infections can be caused by s.aureus?

Answer 7

leading cause of skin and soft tissue infections (SSTIs)

• inflammation of hair follicles
• Carbuncle: larger deeper lesions created by a cluster of furuncles

Question 8

What are toxin mediated s.aureus diseases

Answer 8

-Staphylococcal scalded skin syndrome SSSS toxin(extensive ecfoliative dermatitis), caused by exfoliative toxin
usually affects young children

-toxic shock syndrome, multi-system disease (when toxin is secreted, infection becomes systemic) caused by TSST-1
TSS is a superantigen
treatment: clean obvious wounds, remove tampons, antibiotics

-food poisoning, enterotoxin, occurs when toxin is ingested with food, nausea, vomiting, diarrhea, toxin acts directly on autonomic nervous system to cause the ilness

Question 9

3 tyoes of virulence factors

Answer 9

1. surface proteins
2. Extracellular enzymes
3. Toxinsd

Question 10

What surface factors are important for virulence?

Answer 10

Protein A
surface protein, binds to Fc part of IgG, inhibits complement cascade, blocks phagocytosis

Clumping factor
Surface-bound coagulase
converts fibrinogen in blood to blood clots made of fibrin that hide bacteria from phagocytic cells

Question 11

Name some extracellular enzyme virulence factors

Answer 11

Catalase: protects from H2O2 and free radicals released after ingestion

Coagulase clots plasma,fibrin clots -> to hide from phagocytosis

Hylauronidase: breaks down hyaluronic acid (connective tissue) helps initiaion and spread of infection between cells

Fibrinolysin

DNase

Lipase

Question 12

What toxins has S.aureus?

Answer 12

Haemolysins
Leucocidins
Enterotoxins
TSST
SSSS toxin

Question 13

Name 2 important CoNS

Answer 13

frequently involved in nosocomial and opportunistic infections

S.epidermidis
endocarditis, bacteremia, UTI, medical device infections, produce slime: biofilms in medical implants

S.saprophyticus
cause of UTIs in young femals