Microbiology Flashcards
What is virulence?
The capacity of a microbe to cause damage to the host
What is the pathogenesis of bacteria entering a host cell?
1) Host contact, colonisation, adheres and invades
2) Evade host defences
3) Multiply/ complete its life cycle
4) Exit host- host is undamaged
Name some virulence factors
Adhesin, Invasin, Impedin, Aggresin, Modulin
In relation to virulence factors, what is an adhesion?
- Enables binding of the organism to host tissue
- Specific adhesions determines differences in strains
- Contributes to the ability to colonise
In relation to virulence factors, what is an invasin?
-Enables the organism to invade a host cell/tissue
In relation to virulence factors, what is an impedin?
-Enables the organism to avoid host defence mechanisms
In relation to virulence factors, what is an aggressin?
-Causes damage to the host directly
In relation to virulence factors, what is a modulin?
-Induces damage to the host indirectly
What percentage of people carry Staph Aureus permanently and what percentage transiently?
- 10-20% permenantly
- 40-60% transiently
How specific are nosocomial strains of Staph Aureus?
They can be traced back to individual patients e.g. MRSA
How does community acquired Staph Aureus tend to present?
-Abscess and rash
How does nosocomial acquired Staph Aureus tend to present?
-Immunocompromised, more difficult to treat, very flexible organisms
How does each organism cause a differing range of effects?
Not every strain carries every virulence factor
What is Panton Valentine Leukocidin (PVL)?
- A cytotoxin, Beta pore forming toxins from Staph Aureus
- It has a specific toxicity for leukocytes and attacks WBCs
What is toxic shock syndrome?
-One of the virulence factors of Staph Aureus, super antigens
What is associated with Toxic Shock Syndrome?
Fever, hypotension, 3 organs involved
What is Necrotising Pneumonia and what causes it?
- Rapid progression, multi-organ failure
- Caused by PVL and alpha exotoxin from Staph Aureus
What are the virulence factors specific to Staph Aureus?
-Adhesins, PVL, Superantigens (TSST-1)
What is the major of adhesins in Staph Aureus?
90% are joints, fibrinogen binding protein
What 3 skin infections are associated with Strep pyrogenes?
Impetigo, Cellulitis (Erysipelas), Necrotising fasculitis
What is cellulitis?
Deeper skin infection in the dermis that is not associated with necrosis
What is erysipelas?
- Similar to cellulitis, infection of upper dermis and superficial lymphatics, usually caused by beta haemolytic group A strep
- More superficial than cellulitis, more raised and demarcated
What is Impetigo?
- Highly contagious
- Through contact with discharge on the face
- Infection if below the surface
What is Necrotising fasciitis?
- “Flesh-eating disease”
- Invasive Strep A strains penetrate mucus membrane and develop in lesions
- Rapidly destroys connective tissue
What is the Lancefield System?
- Sereotyping of cell wall carbohydrate
- Major sereotypes are A-H and K-V
What are the major M protein antigens in the Lancefield System?
M1+ M3= major sereotype
M3+ M18= severe invasive disease
What are the differences in presentation of Toxic Shock Syndrome in Staph Aureus and Strep Pyrogenes?
Staph Aureus
- Localised infection
- No bacteremia
- Menstral TSST-1
- Non menstral SEB or SEC
- Pyrogenic Toxin
- Virulence factor
Strep Pyrogenes
- Invasive disease
- Spec A and Spec C (most common toxin)
- Pyrogenic toxin
- Virulence factor
What antibiotic should be used in Staph Aureus infections?
Flucloxacillin
Give 3 examples of toxins produced by Staph Aureus
Enterotoxin (food poisoning)
SSSST (staph scalded skin syndrome toxin)
PVL (panton Valentine Leukocidin)
What is the organism which causes urinary tract infections in women of child-bearing age?
Staph saprophyticus
Name a toxin produced by Beta Haemolytic Streptococci
Haemolysin
What does group A and group B Beta haemolytic Streptococci cause?
Group A: throat, severe skin infections
Group B: meningitis in neonates
What is the difference between resident bacterial flora and transient bacteria?
Resident: organism can be deep in hair follicles and hard to wash away
Transient: can get rid of with hand washing
Give examples of bacterial skin infections that Staph Aureus can cause
Boils and Carbuncles Cellulitis Infected eczema Impetigo Wound infection Staphylococcal scalded skin syndrome
What is the difference between a boil and a carbuncle?
Boil: skin is traumatically pulled out of follicle
Carbuncle: Deeper infection, ofter at the nape of the neck at the hair line. Requires oral flucloxacillin
What is impetigo?
- Contagious superficial infection caused by Staph Aureus
- Lesions well defined and start around nose and face with honey coloured crusts on erthyematous base
- Usually seen in children aged 2-5 years
What is cellulitis?
- Acute infection of skin and soft tissue
- Caused by staph aureus and group A Beta haemolytic strep
- Deeper and less well defined than Erysipelas
What is Staphylococcal Scalded Skin?
- Widespread formation of fluid filled blisters that are thin walled and easily ruptured
- Most common in neonates
- Agressive antibiotics and rehydration due to loss of fluid due to weeping of skin
- Mucous membranes are spared
What is Erysipelas?
- Sharply defined superficial infection caused by Strep pyrogenes
- Often affects the face, unilateral, with increased WBC and fever
- Systemic Penicillin
