Microbiology Flashcards
What is virulence?
The capacity of a microbe to cause damage to the host
What factors are responsible for the variation in virulence between different species?
Adhesin Invasin Impedin Aggressin Modulin
How do Adhesins contribute to virulence?
Allows the organism to bind to host tissue
How do Invasins contribute to virulence?
Allows the organism to invade a host cell/tissue
How do Impedins contribute to virulence?
Lets the organism to avoid host defense mechanisms
How do aggressins contribute to virulence?
Cause damage to the host directly
What organisms make up the skin microbiota?
- Staphylococci spp. (Coag -ve)
- Staphylococcus aureus
- Diptheroids (P.acnes)
- Streptococci spp.
- Bacillus spp
- Candida spp.
- Malassezia furfur
Mycobacterium (occasionally)
What superficial lesions can a staph aureus infection cause?
Boil Carbuncle Abscess Folliculitis Impetigo
What Toxinoses can be caused by a staph aureus infection?
Toxic Shock
Scalded Skin Syndrome
How does Fibrinogen binding protein contribute to virulence?
It is an Adhesin
=> allows Staph Aureus to bind to host cells and infect
How does Leukocidin (PVL) contribute to Virulence?
Kills leukocytes
What is Toxic Shock Syndrome Toxin (TSST-1) and how does it contribute to virulence?
superantigen secreted by Staph. aureus
CAUSES:
- rash
- shock.
- desquamation
Give examples of adhesins found on Staph. Aureus
- Fibrinogen-Binding (ClfA ClfB)
* Collagen-Binding (CNA)
What is the Toxic Shock diagnostic criteria?
- Fever – 39˚C
- Diffuse Macular rash & desquamation (“sunburn”)
- Hypotension – ≤ 90 mm Hg (adults)
- ≥ 3 Organ systems involved – liver, blood, renal, mucous membranes, GI, muscular, CNS.
Panton-Valentine Leukocidin (PVL) gives rise to what severe skin diseases?
- recurrent furunculosis
- sepsis/necrotising fasciitis
PVL & alpha-toxin associated with MRSA causes what?
- necrotizing pnuemonia
- contagious severe skin infections
What skin conditions does Strep. Pyogenes cause?
- Impetigo
- Cellulitis (Erysipelas)
- Necrotising Fasciitis
How do modulins contribute to virulence?
Causes damage to the host indirectly
How are Strep. Pyogenes classified?
Lancefield (Serotyping of Cell Wall Carbohydrate)
What are the Major classifications of Strep. Pyogenes?
Major serotypes A-H and K-V (20)
How is Group A Strep. Pyogenes further classified?
further subdivided according to M protein antigens
- M1 and M3 major serotype
- M3 and M18 severe invasive disease
Is intact skin more or less likely to become infected?
Less likely
infection is more common if skin is broken
How does dry skin protect from infection?
completely dries out the microorganisms
How does sebum contribute to protecting against infection?
The fatty acids found in sebum inhibit bacterial growth
Give an example of transient bacteria flora
MRSA
intermittent => doesn’t always show up in screening
What is the difference between pathogens and commensals?
Pathogens have the potential to cause disease
Commensals don’t necessarily cause any illness
Give examples of competitive bacterial flora
- Staphylococcus epidermidis
- Corynebacterium sp. (diphtheroids)
- Propionibacterium sp.
Give examples of alpha-haemolytic Streptococci
Strep. pneumonia
Strep. viridans (commensal/endocarditis)
Give examples of Beta-haemolytic streptococci
Group A (throat, SKIN) Group B (neonatal meningitis) Groups C,G
GIve examples of non-haemolytic streptococci
Enterococcus (gut commensal, UTI)
Give an example of a coagulase positive and coagulase negative strain of Staphylococcus
Coag. Positive = Staph Aureus
Coag. Negative = Staph. epidermidis
Is staphylococcus an aerobe or an anaerobe?
Aerobic and facultatively anaerobic
=> grows best aerobically but can grow anaerobically
Name toxins that can be produced by some variations of staphylococcus
- Enterotoxin –food poisoning
- SSSST –staphylococcal scalded skin syndrome toxin
- PVL –Panton Valentine Leucocidin
What antibiotic is used to treat staph. aureus infection?
FLUCLOXACILLIN
What can be used to treat MRSA?
Doxycycline
Co-trimoxazole
Clindamycin
if bloodstream involved = Vancomycin
If a patients blood cultures are consistently showing positive staph epidermidis, what must you consider?
Infection from an artificial material in the body
e.g. new heart valve, catheter, IV line
What skin problems can staph. aureus infection cause?
- Boils and Carbuncles
- Minor skin sepsis (infected cuts etc.)
- Cellulitis
- Infected eczema
- Impetigo
- Wound infection
- Staphylococcal scalded skin syndrome
Is streptococcus aerobic or anaerobic?
Aerobic (and facultatively anaerobic)
=> grows best in air, but can grow without
What skin conditions can be caused by group A streptococcus?
- Infected eczema
- Impetigo
- Cellulitis
- Erysipelas
- Necrotising fasciitis
What is necrotising fasciitis?
Bacterial infection spreading along fascial planes below skin surface →rapid tissue destruction
How do we differentiate between the two types of necrotising fasciitis?
Type 1 –mixed anaerobes and coliforms, usually postabdominal surgery
Type II –Group A Strep infection
How is necrotising fasciitis usually managed?
Surgical removal and antibiotics
Based on organisms isolated from tissue taken at operation
What is ‘Tinea’ the latin word for? And therefore what does ‘Tinea Pedis’ mean?
Tinea = ringworm (aka a FUNGAL infection)
Tinea pedis (athlete’s foot)
Describe the pathogenesis of a Dermatophyte (fungal infection)
- Fungus enters soggy skin
- Hyphae spread in keratin layer
- Infects keratinised tissues only (skin, hair, nails)
- Increased epidermal turnover => scaling
- Inflammatory response
- Hair follicles and shafts invaded
- Lesion grows outwards/ heals in centre
=> “ring” appearance
Who is more commonly affected by ringworm infections and where?
Males more commonly affected (Foot and groin)
Scalp ringworm mainly affects children
What sources of fungal infection are there?
Other infected humans (anthropophilic)
Animals (cats, dogs, cattle) (zoophilic fungi)
Soil (geophilic fungi)