STAPHYLOCOCCUS


STAPHYLOCOCCUS SPECIES 





 Define staphylococcus 
This is a Gram positive grape like cocci occurring in clusters or groups
 List the species of staphylococcus 
  • Staphylococcus aureus
  • Staphylococcus epidermidis
  • Staphylococcus saprophyticus

 Mention the species of medical importance
  Staphylococcus aureus

Describe the normal habitat staphylococcus aureus
  Widely distributed in the environment.
  They form part of normal flora of the skin, upper respiratory tract and GIT.
  Staph.  aureus is carried in nose of healthy persons and its pathogenic.
 Describe the morphology staphylococcus aureus
  Gram positive cocci.
  Occur in groups(clusters),two and single.
  Are non motile.
  Are non capsulated.
  Measures about 1um in diameter.



 Describe the mode of transmission and pathogenicity staphylococcus aureus 
staphylococcus aureus is transmitted :-
  • Through skin lesion or wound
  • Ingestion though contaminated food
PATHOGENICITY
  • Staphylococcus aureus causes:-
  • Abscesses.
  • Styles.
  • Impetigo.
  • Wound infections(secondary infection).
  • Conjunctivitis especially in new born
  • Mastitis(inflammation of the breasts).
  • Food poisoning.
  • Secondary infection of insect bites/ulcers, skin, wound and skin disorders
  • Cross infection in hospital
  • Septicemia
  • Endocarditis
  • Osteomylitis
  • Pneumonia eczemia
  • Toxic shock syndrome
 Enzymes and Toxins produced by staphylococcus aureus
Enzymes
The above pathogenicity is due to production/secretion of enzymes and toxins
These enzymes enable the bacteria to attack an individual and cause a disease or an infection. They include:-
  Coagulase-clots plasma
  Staphylokinase
  Hyaluronidase-Destroys connective tissues.
  Beta lactamase
  Lipase-Breaks down fats
  Deoxyribonuclease-Destroys DNA
TOXINS
Leucidin-Kills WBC
  • Lytic toxin(Exotoxin)-Destroy RBC
  • Exfoliatin-Peeling of the skin
  • Enterotoxin-Food poisoning.


 Describe the laboratory diagnosis staphylococcus aureus
1.SPECIMENS
  Pus                from infected sites
  Swabs
  Sputum
  CSF
  Blood for culture
  Feaces
  Vomit                        if food poisoning is suspected
  Food  remains
2.CULTURE
  Staphylococcus aureus grows well aerobically and anaerobic ally(facultative anaerobe).
  Temperature range for growth is10-420c optimum is 35-370c.
  Staph. aureus grows on Blood agar, CBA,MACC and Mannitol salt agar(MSA).Colonies will appear as shown below in each media:-
i)BLOOD AGAR AND CHOCOLATE AGAR
  Produces yellow-cream colonies 1-2mm in diameter after an overnight incubation.
  Some colonies are Beta-haemolytic when grown aerobically.
  Colonies are slightly raised.
(ii)MACCONKEY AGAR
  Smaller colonies of 0.1-0.5mm grow.
  Most strains are lactose fermenters.
  NB;Mannitol salt Agar is selective for growth of staphylococcus aureus.
3.BIOCHEMICAL TESTS
Staphylococcus aureus is identified using the following tests:-
  Catalase test positive.
  Coagulates test positive.
  DNase test positive.

NB:Staphylococcus epidermidis and Staphylococcus saprophyticus are normal flora. They are;-Catalase +ve, coagulase –ve and DNase –ve. 

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