Staphylococcus Flashcards
Cellular features of staphylococcus
1ym diameter
Gram positive cocci
Irregular arrangement
Non sporing
Non motile
Colonial features of staphylococcus
Catalase positive
Resistant to dry salty conditions
2-3 mm size
Circular and smooth
Grey,white, yellow or gold
Catalase test
Hydrogen peroxide + catalase enzyme = H20 + O2
Based on cellular, colonial and catalase characteristics a … .. can be made
Presumptive ID
Coagulase test methodology
Citrates human plasma
Suspected staph species
Incubate for 37 degrees for 30 mins
Disadvantage of a presumptive ID
Cannot make a definite identification based on physical characteristics, requires further testing
Staph genus is split…
By the coagulase test
Coagulase test
Fibrinogen into fibrin
Fibrin causes
Plasma clots
example of Coagulase positive Staph
Staphylococcus aureus
Example of Coagulase negative staph
Staphylococcus epidermidis
Other than S.epidermidis, name two CNS
S. haemolyticus
S.saprophyticus
S. epidermidis (about)
Is commensal so everyone is always colonised
spread endogenous
S. epidermidis makes up to …
75% of CNS clinical samples
s.aureus can be
Haemolytic
S.aureus constantly colonises ?% of the population
30%
S.aureus can be spread both
Endogenous and exogenous
4 ways s.aureus can be spread
Hands, skin shedding, dust and clothes
4 ways to further test what staphylococcus species is present
Mannitol salt agar
Staph latex agglutination
DNase
API staph test
Virulence definition
the severity or harmfulness of a microorganism
Types virulence factors of s.aureus (3)
Toxins
Enzymes
Cell surface proteins
S.aureus cell surface proteins (3)
Protein A
Clumping factor
Fibronectin binding protein
What are exotoxins
Toxins that disrupt membrane activity in host cells
Exotoxins secreted by s.aureus
a,b,d,y haemolysins
Haemolysins are
Pore forming toxins that create holes in cell membranes, impacting integrity causing lysis
Protein A
Interferes with hormonal immune response by inhibiting phagocytosis
Clumping factor
Causes plasma clotting that hides the pathogen from the immune system
Enzymes secreted by s.aureus (4)
Hyaluronidase
Collagenase
Elastase
Lipase
Two superantigens s.aureus
Toxic shock syndrome toxin
Staphylococcal entertoxin
How do super antigens work?
Interacting with APC and T cells causing T cell proliferation and massive cytokine production
What colour does manitol salt agar ferment s.aureus
Yellow
What colour does mannitol salt agar ferment CNS
Pink
Latex agglutination test CNS
Negative
Latex agglutination test s.aureus
Positive
DNase result s.aureus
Yellow ferment
DNase result CNS
None
