bacterial virulence

Question 1

what is impedin

Answer 1

enables the organism to avoid host defence mechanisms

Question 2

what is aggressin

Answer 2

causes damage to the host directly

Question 3

what is modulin

Answer 3

induces damage to the host indirectly

Question 4

what are the main staphylococcal infectons of the skin

Answer 4

S.aureus

• 20%-(60%) colonisation (carriage)
• coagulase positive
• nasal strain can protect

S.epidermis

• 100% colonisation
• skin and mucosa membranes
• coagulase negative

Question 5

explain the pathology of S.aureus

Answer 5

Superficial lesions - boil to abscesses

Systemic - life threatening

Toxinoses - toxic shock, scaled skin syndrome

Question 6

what are superantigens

Answer 6

Common theme disrupting immune system and coordination by over stimulation. Activate 1 in 5 T cells. TSST-1 in particular is associated with toxic shock. Massive release of cytokines and inappropriate immune response.

Question 7

what is diagnostic criteria for toxic shock syndrome

Answer 7

Fever 39*
Diffuse macular rash and desquamation
Hypotension < 90 mmHg (adults)
>3 organ systems involved eg liver, blood, renal, mucous membranes

Question 8

what are adhesions

Answer 8

extra cellular matrix molecules present on epithelial, endothelial surfaces as well as components of blood clots

Question 9

what is panton-valentine leukocidin

Answer 9

• A toxin produced by certain types of staph aureus
• Specific toxicity for leukocytes
• PVL associated with severe skin infections
• PVL and alpha-toxin associated with CA-MRSA responsible for necrotising pneumonia and contagious severe skin infections

Question 10

what is streptococcus pyogenes

Answer 10

common presentation as pharyngitis or streptococcal sore throat, scarlet fever

• Group A streptococci
• Skin infections can be impetigo, cellulitis, necrotising fasciitis

Question 11

what is the lance field system

Answer 11

Lancefield grouping is a system of classification that classifies catalase-negative Gram-positive cocci based on the carbohydrate composition of bacterial antigens found on their cell walls.

Question 12

what are GAS skin diseases

Answer 12

• Impetigo (usually face)
• Cellulitis - deeper skin infection in the dermis that is not associated with necrosis
• Erysipelas (localised) - fever, rigours and nausea

Question 13

how can new strains of a disease emerge

Answer 13

horizontal gene transfer

Question 14

what do opportunistic infections and toxinoses depend on

Answer 14

genotype and expression of virulence proteins

Question 15

what are some pyogenic infections caused by staph aureus

Answer 15

• boils, carbuncles
• surgical site infection
• abscesses
• impetigo
• mastitis
• pneumonia eg ventilator assisted
• endocarditis

Question 16

what are some toxin-mediated infections

Answer 16

• scaled skin syndrome
• pemphigus neonatorum
• toxic shock syndrome
• food poisoning

Question 17

what is the effects of s aureus manipulating B cells

Answer 17

inability to develop adaptive immunity

Question 18

what is the effect of s aureus manipulating plasma blasts

Answer 18

inability to develop adaptive immunity

Question 19

what is the effect of s aureus manipulating T cells

Answer 19

inability to develop adaptive immunity

Question 20

how can understanding virulence factors impact on clinical care

Answer 20

• next generation sequencing (more rapid diagnosis)
• molecular techniques (PCR/antibodies etc)
• diagnoses and understanding pathology/risk
• isolation and quarantine
• vaccines/anti-infectives

Question 21

what is a virulence factor

Answer 21

component of micro-organism that can be assigned to its ability to cause that disease

Question 22

what do opportunistic infections and toxinoses depend on

Answer 22

genotype and expression of virulence proteins

Question 23

where are s.pyrogenes normally found

Answer 23

pharynx and also adheres to skin

Question 24

what os the variation in disease and virulence an effect of

Answer 24

variation in genes and the proteins expressed by pathogen