Lecture 8 Flashcards
Is staphylococcus aureus gram positive or negative?
Positive
Is staphylococci motile?
No due to a lack of flagella
How do colonies of staphylococci appear?
Clusters of spherical cells
What conditions can staphylococci can grow in?
resistant to dry conditions and 10% NaCl (Halodurant)
Where is staphylococcus typically found on humans?
On the skin typically in warm moist areas such as the armpits, as well in the nasopharynx, oropharynx, GI tract
How does staphylococcus aureus get transmitted?
From human to human and through objects as it can survive on dry surfaces through its capsule allowing it to be one of the major hospital acquired infections
What are the two strains of staphylococci aureus?
Hospital acquired and Community acquired
What is the difference between community acquired and hospital acquired staphylococcus aureus?
Hospital Acquired infections tend to be more resistant through increased antibiotic resistance
What types of antibiotic resistance does staphylococcus aureus possess?
Almost all resistant to penicillin, a few stands resistant to methicillin and vancomycin
What provides the resistance to penicillin in staphylococcus aureus?
A beta-lactamase gene
What are the two diagnostic tests for staphylococcu aureus?
- Test for gram +ve
- +ve catalase test
- +ve coagulase test
OR
Appearance of pink bacterium on mannitol salt agar
What virulence factors does staphylococcus aureus posses?
Microbial surface components recognising adhesive matrix molecules, Cytolysins, Exfoliative toxins various spreading factors, Toxic shock syndrome toxin, Staphylococcal enterotoxin, Various immune evasion factors
What are microbial surface components recognising adhesive matrix molecules?
Cell wall proteins on gram positive bacteria allowing the bacterium to bind to the extracellular matrix
What cytolysins does S. Aureus use?
Alpha, Beta, Gamma, Delta and Panton-Valentine leukocidin
What is the function of alpha toxin?
To form membrane pores compromising cell membranes killing them
What is the function of beta toxin?
Hydrolysis of membrane phospholipids
What is the function of Delta toxin?
Detergent like action
What is the function of Gamma and Panton-Valentine leukocidin
pore forming toxins
What group of toxins is unique to S.Aureus?
Exfoliative toxins
What is the function of ETA and ETB?
Serine proteases that cleave desmosomes causing skine peeling but no inflammation
What are the spreading factors of S.Aureus?
Lipases, Nucleases, Hyaluronidase, Proteases, Staphylokinase
What is the function of Staphylokinase?
Fibrinolysis (clot breakdown)
What is the function of Hyaluronidase?
Hydrolysis of hyaluronic acid in connective tissue
What are the super antigens of S.Aureus?
Toxic shock syndrome toxin, Staphylococcal enterotoxins
What is the function of the superantigens?
Trigger large release of pro inflammatory cytokines causing damaging systemic inflammation and potentially food poisoning
What are the immune evasion factors of S.Aureus?
Capsule, Slime Layer, Catalase, Clumping factor CIF-A, Protein A
What is the function of catalase?
To reduced the toxic oxidative radicals produced by the immune system to kill the pathogen
What is the function of Clumping factor CIF-A?
Creates a capsule of fibrin around the cell resulting in a disguise from phagocytosis and oponisation
What is the function of Protein A?
Bind to Fc regions of antibodies handcuffing them to prevent their functions
What are the diseases caused by S.Aureus?
Impetigo, Folliculitis, Boils, Carbuncles, Bacteremia and endocarditis, Osteomyelitis, Septic Arthritis, Staphylococcal Scalded skin syndrome, Pneumonia, Staphylococcal Food poisoning, Toxic shock syndrome
What is impetigo?
Localised skin infection where a pus filled vesicle is formed, typically affects young children
What is Folliculitis?
impetigo on hair follicules
What is a boil?
Painful pus filled nodule
What are Carbuncles?
Boils that extend beyond the skin and thus can cause systemic disease
What is Bacteremia and Endocarditis?
Spread of bacteria into blood, and to the heart causing endocarditis and often resulting in damage to endothelial cells through secretory enzymes
What is Osteomyelitis?
Infection in bone, usually at the tip
What is septic arthritis?
Infection in the joint space, mainly in children and young adults
What is staphylococcal Scalded Skin Syndrome?
Blisters on the skin, desquamation of epithelium caused by exfoliative toxins. Most common in new borns or premature babies
What is pneumonia?
S.Aureus causes necrotising pneumonia through use of cytolytic toxins forming abscess’ in lungs
What is staphylococcal food poisoning?
Microbial intoxication caused by SEA and SEB lasting for only 24 hours as it is an acute reaction
What are the two forms of toxic shock syndrome?
Menstrual and non menstrual
What is menstrual toxic shock syndrome?
Growth of bacteria in bagina caused by prolonged usage of tampons
What is non-menstrual toxic shock syndrome?
Superantigen producing bacteria grows in a wound
What are the key risk factors for S.Aureus caused disease?
Presence of foreign body which penetrates the skin, including poor hygiene of hospital staff of supression of native flora and lack of antibodies due to use of antibiotics
