Key Bacteria - Staphylococci Flashcards
Give 7 key characteristics for all Staphylococci bacteria?
- Gram positive
- Cocci
- In clusters
- non-motile
- non-spore forming
- Facultative anaerobic
- Either coagulase positive or negative
What is the structure of Staphylococcus aureus?
Gram positive Cocci bacteria
In clusters
Where is Staph. aureus found?
Found on skin and mucous membranes
How is Staph. aureus spread?
Contagious spread, from person to person.
Examples of conditions commonly linked to Staph. aureus infection?
- Sepsis
- Pneumonia
- Localised skin infections
- Cellulitis
- Endocarditis
- Abscesses
- Co-morbidities & immunosuppression
Staph. aureus virulence factors?
- Capsule
- Coagulase enzyme
- Cytotoxic exotoxins
- Protein A
- Fibronectin-binding protein
- Clumping factor
- Superantigen exotoxins
Explain the Capsule, as a virulence factor of Staph. aureus?
Enables inc. resistance to phagocytosis
Explain Protein A as a virulence factor of Staph. aureus
Binds to Fc region of IgG antibodies, and acts as an anti-opsin.
Explain Fibronectin-binding protein as a virulence factor of Staph. aureus
Promotes binding to mucosal cells & tissue matrices
Explain Coagulase enzyme as a virulence factor of Staph. aureus?
Enzyme catalyses breakdown of fibrinogen to form clot
Explain Clumping factor as a virulence factor for Staph. aureus?
This FnBP (…) enhances clumping of the organism in the presence of plasma
Explain cytotoxic exotoxins as a virulence factor for Staph. aureus?
Exotoxins are toxic to, and attack mammalian cells. Cause lysis of cells.
Explain superantigen exotoxins as a virulence factor of Staph. aureus?
Affinity for T-cell receptor—MHC Class 2 Antigen complex.
The toxins stimulate an enhanced T lymphocyte response.
Causes toxic shock by release of large amounts of T-cell cytokines
(Potential link to DIC)
Investigations for Staph. aureus infection?
- Full blood count = inc. WBC, neutrophils etc.
- CRP (signifies inflammation)
- blood culture — swab for gram stain
- Coagulase test = positive result
Treatment for Staph. aureus infection?
Antibiotics
- Flucloxacillin = inhibits formation of cross links in thick peptidoglycan cell wall (Staph. aureus = gram positive)
- Amoxicillin = same effect
- Amoxiclav = use when resistant to amoxicillin
- Vancomycin = for MRSA
What is the structure of Staph. Epidermidis?
Gram positive, cocci bacteria
Where is Staph. epidermidis found?
Present normally on skin and mucous membranes
How is Staph. epidermidis infection spread?
- Contagious spread person to person
- Biofilm = allows it to spread from surface to person
Contraction - Key clinically relevant HAI
- on catheters, prosthetic devises & heart valves
Examples of conditions commonly linked to Staph. epidermidis?
- Skin infections
- Sepsis
- Prosthetic device & heart valve infections
- Endocarditis (infection of the heart valves and parts of the inside lining of the heart muscle)
- Catheter infections (catheter-induced UTIs)
Staph. epidermidis virulence factors?
- Biofilm production
- Capsule
Explain Biofilm as a virulence factor of Staph. epidermidis?
Extracellular (glycocalyx) “slime” production that:
- Acts as a glue adhering it to surfaces and cells
- Also acts as a diffusion barrier to host defences and antibiotics, causes resistance to phagocytosis and some antibiotics (e.g. vancomycin)
Investigations for Staph. epidermidis infections?
- Full blood count
- Blood cultures = gram +ve cocci (clusters)
- CRP
- Coagulase test = coagulase negative
Treatments for Staph. Epidermidis?
Antibiotics
- vancomycin
- or rifampin if vancomycin resistant
