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What are the components of Aerobic Gram Positive cocci?

  • Staphylococci (clusters) 
  • Streptococci and Enterococci (chains)


What is the result of coagulase test in differentiating Staphlococci?

Coagulase-positive=Staphylococcus aureus which can be either MRSAor MSSA.

Coagulase negative=nothing


Descibe the characteristics of Staphylococcus aureus?

  • Commensal organism carried in nose, axilla, perineum.
  • Wide range of disease from boils/abscesses and soa issue infections to septecaemia and osteomyelits.
  • Commonly penicillin resistant due to production of penicillinase.


What are the coagulase-negative staphylococci?

  • Many different species e.g. S. epidemidis
  • Mainly skin commensals.
  • Form biofilms and may be significant pathogens in the presence of foreign bodies/prostheses e.g. prosthe@c heart


What are the properties of Streptococci?

• α- haemolytic (partial haemolysis)

-> turn blood agar green

• β-haemolytic (complete haemolysis)

-> turn blood agar clear

• Non haemolytic


Give an example of α-haemolytic streptococci?

Streptococcus pneumoniae

-> pneumonia, meningitis, septecaemia


What are the feutures of β-haemolytic streptococci?

  • Further identified by carbohydrate surface antigens.
  • further identified by Groups A-G.

• A, B, F and D clinically most important.



What are the constituents of Gram positive bacilli?

  • Aerobic 
  • Anaerobic:Clostridium tetani,Clostridium perfringens and Clostridium difficile.


What are the feutures of Clostridium difficile?

  • “Difficult” to culture. 
  • Asymptomaticc gut carriage in healthy people

. • Important cause of diarrhoea, associated with toxin production and potentially fatal


What are the feutures of Clostridium perfringens?

  • Found in soil and normal commensal in human and animal gut/faeces.
  • Can contaminate food


What are the feutures of Clostridium tetani?

  • Toxin production by C. tetani cause tetanus.

• Uncontrolled muscle spasm due to loss of inhibition at neuromuscular junction.



Gram negative flow chart


Gram postive flow chart