Bacterial Virulence Flashcards
define pathogenicity and virulence
pathogenicity - ability of organism to cause disease
virulence - degree of pathology (harm) caused by organism
what are virulence factors
characteristics that enhance a bacteriums pathogenicity
impendin
avoid host defence mechanisms
agressin
cause damage to host directly
modulin
induce damage to host indirectly
what are superantigen exotoxins
have an affinity for the T cell MHC class II antigen complex, stimulate enhanced t cell response
what is TSST-1 and what does it cause
superantigen TSS
what does PVL do
make strains more virulent , specific toxicity for WBC
what can PVL cause
severe skin infection eg necrotising fasciitis, pneumonia and sepsis
people are unusually sick
what is PVL produced by
predominantly CA MRSA
what are the treatment options for MRSA
include Doxycycline, Co- trimoxazole, Clindamycin, Vancomycin (not Flucloxacillin).
what is necrotizing pneumonia
Pneumonia characterised by the development of the necrosis within infected lung tissue
what can necrotizing pneumonia lead to
ARDS, deterioration in pulmonary function and multi organ failure
what are the CF of TSS
high fever, rash, diffuse erythema followed by desquamation, vomiting and diarrhoea
what does the rash resemble in TSS
sunburn
what does the BP do in TSS
hypotension
what causes TSS
S Pyogenes and S Aureus
staphylococcal scalded skin syndrome characteristics
red blistering skin
SSSS cause
S Aureus releases exfoliative toxin that causes blistering of the skin, ETA and ETB toxins target desmoglein 1
where are desmogleins found
in keratinocytes
where is S pyogenes normally found
pharynx
what is S pyogenes classified using
lancefield classification - group A strep
what is S pyogenes
lancefield: group A strep
group beta-haemolytic streptococci
what does the lancefield classification use
based on carbohydrate composition of bacterial antigens found on cell wall
what is special about S pyogenes structure
the capsule is made from hyaluronic acid which is identical to that found in human connective tissue - not recognised as foreign by body
what does S pyogenes cell wall contain
M proteins - needs these to be infectious
what is impetigo
highly contagious skin infection that causes sores and blisters - classical honey coloured crust
what is impetigo caused by
S pyogenes is the classic cause, S aureus has been responisble for more recent cases
what would you treat impetigo systemically
penicillin - effective against both aureus and pyogenes
where about is the infection in impetigo
immediatly below surface (stratum corneum) typically face (children)
what is cellulitis
Generalised term for a spreading infection in the dermis that isn’t associated with necrosis
Often affects the lower leg, causing an upward-spreading, hot erythema, and occasionally will blister. Patients often unwell with high temperature.
Caused by b-Haemolytic Streps and Staphs
what do you treat cellulitis with
flucloxacillin
erysipelas
a superficial form of cellulitis caused by S pyogenes
what are the clinical features of erysipelas
sharply defined superficial infection
fever, rigours nausea
what is Necrotising fasciitis
bacterial infection that spreads along fascial planes below skin surface causing rapid tissue destruction
what causes type I Necrotising fasciitis
mixed anaerobes and coliforms, usually post abdo surgery
what causes type II Necrotising fasciitis
group A strep infection
what is a ringworm also called
tinea
cruris
GROIN
capitis
scalp
manuum
hand
unguium
nails
tinia pedis
athletes foot
what are dermatophytes
fungi that require keratin for growth
describe the invasion of dermatophytes
fungus enteres the skin and hyphae spread through stratum corneum (dermatophytes require keratin for growth so only keratinised tissues are infected)
inc epidermal turnover = scaling
inflammatory response provoked
what is the appearance of dermatophyte lesion
ring like
- grows outwards and heals in the centre
who is scalp ringworm (tinea capitis) most common in
children
who is tinea pedis and cruruis most common in
men
what is the most likely causative organism of ringworm
Trichophyton rubrum
Trichophyton mentagraphytes
Microsporum canis (cats and dogs to humans)
what do you treat ringworm with
clotrimazole cream
topical nail paint - amorolfine
systemic involvement - oral terbinafine
what can you treat scalp ringworm infections with
terbinafine orally and itraconazole orally
what is candida
most common yeast infecion
where is candida found
skin folds where area is warm and moist
what is candida treated with
clotrimazole cream, oral flucanazole
what is the parasitic infection scabies caused by
sarcoptes scabiei
what is the chronic crusted form of scabies called
norwegian scabies
what is the incubation period of scabies like
up to 6 weeks
treatment of scabies
malathion lotion
benzyl benzoate in children
scabies CF
intensely itchy rash affecting finger webs, wrists and genital area
what is the treatment for lice
malathion
what is vagabonds disease
pediculus corporos
what colour do alpha haemolytic streptococci go
green (partial)
what colour do beta haemolytic streptococci go
yellow (full)
