bacterial virulence Flashcards
what is impedin
enables the organism to avoid host defence mechanisms
what is aggressin
causes damage to the host directly
what is modulin
induces damage to the host indirectly
what are the main staphylococcal infectons of the skin
S.aureus
- 20%-(60%) colonisation (carriage)
- coagulase positive
- nasal strain can protect
S.epidermis
- 100% colonisation
- skin and mucosa membranes
- coagulase negative
explain the pathology of S.aureus
Superficial lesions - boil to abscesses
Systemic - life threatening
Toxinoses - toxic shock, scaled skin syndrome
what are superantigens
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.
what is diagnostic criteria for toxic shock syndrome
Fever 39*
Diffuse macular rash and desquamation
Hypotension < 90 mmHg (adults)
>3 organ systems involved eg liver, blood, renal, mucous membranes
what are adhesions
extra cellular matrix molecules present on epithelial, endothelial surfaces as well as components of blood clots
what is panton-valentine leukocidin
- 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
what is streptococcus pyogenes
common presentation as pharyngitis or streptococcal sore throat, scarlet fever
- Group A streptococci
- Skin infections can be impetigo, cellulitis, necrotising fasciitis
what is the lance field system
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.
what are GAS skin diseases
- Impetigo (usually face)
- Cellulitis - deeper skin infection in the dermis that is not associated with necrosis
- Erysipelas (localised) - fever, rigours and nausea
how can new strains of a disease emerge
horizontal gene transfer
what do opportunistic infections and toxinoses depend on
genotype and expression of virulence proteins
what are some pyogenic infections caused by staph aureus
- boils, carbuncles
- surgical site infection
- abscesses
- impetigo
- mastitis
- pneumonia eg ventilator assisted
- endocarditis
what are some toxin-mediated infections
- scaled skin syndrome
- pemphigus neonatorum
- toxic shock syndrome
- food poisoning
what is the effects of s aureus manipulating B cells
inability to develop adaptive immunity
what is the effect of s aureus manipulating plasma blasts
inability to develop adaptive immunity
what is the effect of s aureus manipulating T cells
inability to develop adaptive immunity
how can understanding virulence factors impact on clinical care
- next generation sequencing (more rapid diagnosis)
- molecular techniques (PCR/antibodies etc)
- diagnoses and understanding pathology/risk
- isolation and quarantine
- vaccines/anti-infectives
what is a virulence factor
component of micro-organism that can be assigned to its ability to cause that disease
what do opportunistic infections and toxinoses depend on
genotype and expression of virulence proteins
where are s.pyrogenes normally found
pharynx and also adheres to skin
what os the variation in disease and virulence an effect of
variation in genes and the proteins expressed by pathogen
