Staphylococcus

Staphylococcus are Gram Positive cocci it is arranged in grapes like cluster. they are the commonest causes of suppuration.

They are medically important species of genus staphylococcus includes

Staphylococcus aureus ( pathogenic infection of man) staphylococcus epidermids staphylococcus saprophyticus. ( skin commensal )

Under the microscope theu appears spherical ( cocci ) and form in grapes cluster.

diagram of staphylococcus in grapes like cluster


Morphology of staphylococcus


They are Gram Positive cocci arranged in groups like cluster non motile and non sporing approximately 1 mm in diameter and it Nanna flagellated organism.


Culture media staphylococcus

They grow rapidly on ordinary culture media.

The optimum temperature is grow 41°C and optimum PH 7.4-7.6

They aerobic and facultative anaerobes

Nutrient Agar for staphylococcus

After overnight of 24 hour incubation the colonies are to 2 to 4 mm in diameter circular smooth convex and easily emulsifiable.

Blood Agar for staphylococcus

Colonies are similar to their nutrient Agar and in addition a beta types is seen. hemolysis is best observed with sheep or rabbit blood.

Macconkey Agar for staphylococcus

Colonies are very small and pink due to lactose fermentation.

Selective media for staphylococcus

These media are used for isolating staphylococcus aureus from simple such as faces containing other bacteria. 

Staphylococci can tolerate 8 to 10% NaCl lithium chloride tolerate and polymyxin 

Biochemical reaction for staphylococcus

  • Catalyst positive 
  • oxidase negative
  • Break down carbohydrate by fermentation 

Disease caused by staphylococcus

  • Food poisoning
  • Deep infection
  • Skin infection

Laboratory diagnosis for staphylococcus

Specimen

These are collected according to the nature of lesion as follows.

  • Pus 
  • sputum 
  • blood 
  • urine 
  • CSF

Collection and transportation

Specimens should be collected in astrology is container under all asptic conditions . sterile swap should be used for collecting specimen for sites such as nose or perineum.

Direct microscopy

Direct microscopy with gram stined smear of pus or wound exudate is useful. where gram positive cocci in clusters may be seen this is no value for specimen we are mixed bacterial flown are normally present e.g sputum.

Treatment of staphylococcus infection

  • Benzyl penicillin is the most effective antibiotic in sensitive strains

  • Vancomycin is used in treatment of infection with MRSA stains.