bacterial virulence

Question 1

what is the definition of virulence ?

Answer 1

The capacity of a microbe to cause damage to the host.

Question 2

List the virulence factors responsible for the variation in virulence within & between species

what are the 2 remaining virulence factors ?

Answer 2

adehsin, impedin, aggressin

invasin and modulin

Question 3

define adhesin

Answer 3

Enables binding of the organism to host tissue.

They are extra cellular matrix molecules present on epithelial, endothelial surfaces as well as a component of blood clots.

Question 4

define invasin

Answer 4

enables an organism to invade a host cell/tissue

(Any of a class of proteins associated with the penetration of bacteria into mammalian cells.)

Question 5

define impedin

Answer 5

Enables the organism to avoid host defense mechanisms.

Question 6

what is the difference between aggressin and modulin

Answer 6

aggressin causes damage to the host directly whereas modulin causes damage to the host indirectly.

Question 7

list some of the skin infections caused by staph.aureus (6)

Answer 7

rash, abscess, folliculitis, carbuncle, impetigo, scalded skin syndrome

Question 8

give some examples of toxinoses (disease or lesion caused by the action of a toxin)

Answer 8

TSST-1 and SSC (scalded skin syndrome)

with staph.aureus being a potential cause of them both

Question 9

describe the signs and symptoms for TSST-1 (toxin shock syndrome toxin)

TSST-1 can be produced by some staph.aureus isolates

Answer 9

rapid progression (48 hrs) high fever, vomiting, diarrhea, sore throat, muscle pain

Question 10

describe the signs and symptoms of SSC (scalded skin syndrome)

Answer 10

exfoliatin toxins (are a staph. aureus exotoxin), often neonatal, face, axilla & groin,

– ETA & ETB toxins target Desmoglein-1 (DG-1)

Question 11

what causes an antigen to be classed as a superantigen ?

Answer 11

superantigen cause a massive T cell response where they Activate 1 in 5 T Cells – (normal Ag (antigen) 1:10,000)

Question 12

what type of antigen is TSST-1 classed as ? what disease is it associated with? and what does it cause in terms of the immune system?

Answer 12

superantigen

toxic shock

causes massive release of cytokines & inappropriate immune response.

Question 13

what is the 4 main diagnostic criteria for toxic shock syndrome ?

Answer 13

• Fever – 39˚C
• Diffuse Macular rash & desquamation (shedding of the outermost membrane or layer of a tissue, such as the skin.) – diffuse macular erythroderma (“sunburn”)
• Hypotension – ≤ 90 mm Hg (adults)
• ≥ 3 Organ systems involved – liver, blood, renal, mucous membranes, GI, muscular, CNS.

Question 14

what is PVL ? and what is it produced by ?

Answer 14

Panton-Valentine Leukocidin produced by highly virulent strains of staph aureus.

Question 15

what does PVL have a specific toxicity too ?

Answer 15

leukocytes

Question 16

which severe skin infections is PVL associated with ?

Answer 16

e.g. recurrent furunculosis –

sepsis/necrotising fasciitis

Question 17

what toxins and type of staph.aureus are responsible for necrotizing pnuemonia & contagious severe skin infections?

Answer 17

PVL & alpha-toxin linked with CA-MRSA

Question 18

what are the signs and symptoms of necrotizing pneumonia ?

Answer 18

• Preceding Influenza like syndrome
• Necrotising haemorrhagic pneumonia
• Rapid Progression!
• Acute Respiratory distress
• Deterioration in pulmonary function
• Refractory Hypoxaemia
• Multi-organ failure despite Antibiotic therapy.

Question 19

list some of the skin infections potentially caused by streptococcus pyogenes (3)

Answer 19

Impetigo

Cellulitis (Erysipelas)

Necrotising Fasciitis

Question 20

what is the haemolysis of strep.pyogenes ?

Answer 20

GAS (beta haemolysis)

Question 21

what is used to classify different strep.pyogenes ?

Answer 21

lancefield (surface antigen)

Question 22

what is the lancefield system ?

Answer 22

serotyping (A serotype or serovar is a distinct variation within a species of bacteria or virus or among immune cells of different individuals) of cell wall carbohydrate.

Question 23

what is the variation in diseases and virulence caused by ?

Answer 23

variation in genes

Question 24

where is strep.pyogenes normally found ?

Answer 24

pharynx

Question 25

what does strep.pyogenes adhere too ?

Answer 25

skin

Question 26

what does hyaluronic acid (capsules) help do ?

Answer 26

help reduce phagocytosis of the bacteria, adhesion/evasion

Question 27

where does impetigo usually affect?

Answer 27

face, it is highly contagious through contact with discharge on the face

Question 28

difference between toxic shock caused by staph.aurues and strep.pyogenes

Answer 28

• S. aureus – localised infection – no bacteremia – Menstrual TSST-1 – Non-menstural SEB or SEC – pyrogenic toxin – Virulence Factor • Superantigen
• S. pyogenes – invasive disease (pharyngitis) – SpeA & SpeC most common toxin – pyrogenic toxin – Virulence factor • Superantigen

Question 29

Define what virulence factors are

Answer 29

Virulence factors are molecules produced by pathogens (bacteria, viruses, fungi and protozoa) that contribute to the pathogenicity of the organism and are responsible for the variation in virulence within & between species

Question 30

Appreciate the summary slide

Answer 30

• Virulence & Virulence Factors; the molecular/genetic basis of pathogenesis
• • S. aureus exists as multiple strains colonising skin & mucous membranes
• • Opportunistic infections & Toxinoses dependent on genotype & expression of virulence proteins
• • S. pyogenes normally found in pharynx, also adheres to skin
• • Responsible for range of diseases including several skin conditions & a range of strains & virulence factors
• • Toxic shock produced by both organisms due to production of similar exo-proteins, common virulence factors & disease mechanisms
• • Variation in diseases, & virulence the result of variation in genes.

Question 31

List some of the skin diseases causes by GAS (group A strep)

Answer 31

• Impetigo (usually face)
• Cellulitis
• Erysipelas
• Necrotizing fasciitis