STAPHYLOCOCCUS

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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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