bacterial virulence Flashcards
what is the definition of virulence ?
The capacity of a microbe to cause damage to the host.
List the virulence factors responsible for the variation in virulence within & between species
what are the 2 remaining virulence factors ?
adehsin, impedin, aggressin
invasin and modulin
define adhesin
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.
define invasin
enables an organism to invade a host cell/tissue
(Any of a class of proteins associated with the penetration of bacteria into mammalian cells.)
define impedin
Enables the organism to avoid host defense mechanisms.
what is the difference between aggressin and modulin
aggressin causes damage to the host directly whereas modulin causes damage to the host indirectly.
list some of the skin infections caused by staph.aureus (6)
rash, abscess, folliculitis, carbuncle, impetigo, scalded skin syndrome
give some examples of toxinoses (disease or lesion caused by the action of a toxin)
TSST-1 and SSC (scalded skin syndrome)
with staph.aureus being a potential cause of them both
describe the signs and symptoms for TSST-1 (toxin shock syndrome toxin)
TSST-1 can be produced by some staph.aureus isolates
rapid progression (48 hrs) high fever, vomiting, diarrhea, sore throat, muscle pain
describe the signs and symptoms of SSC (scalded skin syndrome)
exfoliatin toxins (are a staph. aureus exotoxin), often neonatal, face, axilla & groin,
– ETA & ETB toxins target Desmoglein-1 (DG-1)
what causes an antigen to be classed as a superantigen ?
superantigen cause a massive T cell response where they Activate 1 in 5 T Cells – (normal Ag (antigen) 1:10,000)
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?
superantigen
toxic shock
causes massive release of cytokines & inappropriate immune response.
what is the 4 main diagnostic criteria for toxic shock syndrome ?
- 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.
what is PVL ? and what is it produced by ?
Panton-Valentine Leukocidin produced by highly virulent strains of staph aureus.
what does PVL have a specific toxicity too ?
leukocytes
which severe skin infections is PVL associated with ?
e.g. recurrent furunculosis –
sepsis/necrotising fasciitis
what toxins and type of staph.aureus are responsible for necrotizing pnuemonia & contagious severe skin infections?
PVL & alpha-toxin linked with CA-MRSA
what are the signs and symptoms of necrotizing pneumonia ?
- Preceding Influenza like syndrome
- Necrotising haemorrhagic pneumonia
- Rapid Progression!
- Acute Respiratory distress
- Deterioration in pulmonary function
- Refractory Hypoxaemia
- Multi-organ failure despite Antibiotic therapy.
list some of the skin infections potentially caused by streptococcus pyogenes (3)
Impetigo
Cellulitis (Erysipelas)
Necrotising Fasciitis
what is the haemolysis of strep.pyogenes ?
GAS (beta haemolysis)
what is used to classify different strep.pyogenes ?
lancefield (surface antigen)
what is the lancefield system ?
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.
what is the variation in diseases and virulence caused by ?
variation in genes
where is strep.pyogenes normally found ?
pharynx
what does strep.pyogenes adhere too ?
skin
what does hyaluronic acid (capsules) help do ?
help reduce phagocytosis of the bacteria, adhesion/evasion
where does impetigo usually affect?
face, it is highly contagious through contact with discharge on the face
difference between toxic shock caused by staph.aurues and strep.pyogenes
- 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
Define what virulence factors are
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
Appreciate the summary slide
- 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.
List some of the skin diseases causes by GAS (group A strep)
- Impetigo (usually face)
- Cellulitis
- Erysipelas
- Necrotizing fasciitis
