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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