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.