STAPHYLOCOCCI

INTRODUCTION:
  • Family: Micrococceae (consists of Gram positive cocci, arranged in tetrads, clusters)
  • Ogston discovered Staphylococcus in 1881
CLASSIFICATION:
  • Based on pigment production:
  1. S.aureus :-golden-yellow pigmented colonies
  2. S.albus :- white colonies
  3. S.citrus :-lemon yellow colonies
  • Based on pathogenecity:
  1. Pathogenic:- includes only one i.e., S.aureus
  2. Non-pathogenic:- includes S.epidermidis, S.saprophyticus, S.albus, S. citrus, S.hominis,etc.
  • Based on coagulase production:
  1. Coagulase positive: S. aureus
  2. Coagulase negative: S. epidermidis, S. saprophyticus(Infection by coagulase­ negative Staphylococci are due to Staphylococcus epidermidis)
STAPHYLOCOCCUS AUREUS:
  • Natural habitat:-Nostril (30%)and skin
  1. Morphology:-
  2. Gram-positive, cocci, 0.5-1.5µm in diameter; occur characteristically in group, also singly and in pairs
  3. Form irregular grapelike clusters (since divide in 3 planes)& shows Transient colonization
  4. Non-motile, non- sporing and few strains are capsulated
  5. For phage typing23 phages of staphylococcus aureus are used
  6. Catalase positive, beta-hemolytic staphylococcus
CULTURE:
  • Aerobes and facultative anaerobes
  • Opt. Temp. For growth= 37°C
  • Opt. pH for growth= 7.5
  • On Nutrient agar,golden yellow and opaque colonies with smooth glistening surface, 1-2 mm in diameter (max. pigment production@22 °C)
  • On Blood agar,golden yellow colonies, surrounded by a clear zone of hemolysis (beta-hemolysis),esp. When incubated in sheep or rabbit blood agar in atmosphere of 20% CO2
  • On MacConkey agar,Smaller colonies than those on NA(0.1-0.5 mm) and are pink coloured due to lactose fermentation
  • On Mannitol salt agar,
  1. S.aureus ferments mannitol and appear as yellow colonies
  2. MSA is a useful selective medium for recovering S.aureus from faecal specimens, when investigating food poisoning
BIOCHEMICAL REACTION:
  • Catalase positive; oxidase negative
  • 3-lactamase production in Staphylococci is under plasmid control
  • Ferment glucose, lactose, maltose, sucrose and mannitol, with production of acid but no gas
  • Indole test= negative
  • MR test= positive
  • VP test= positive
  • Hydrolyse gelatin
  • Reduces nitrate to nitrite
  • Phospahatase= positive
  • DNA-ase test= positive

Test Staphylococcus aureus Staphylococcus epidermidis
Coagulase Positive Negative
Clumping factor Positive Negative
Heat stable nuclease Positive Negative
Urease Variable Negative
Acid from mannitol Positive Negative
Acid from trehalose Positive Negative
VIRULENCE FACTOR:

Cell wall associated structures Extracellular toxins Extracellular Enzyme
Peptidoglycan
Inhibits inflammatory responseCapsule
Adhere to host cell
Resist phagocytosisprotein
ABinds to Fc moiety of IgG, exerting antiopsomin(strongly antiphagocytic effect)Clumping factor (bound coagulase)
Cause organism to clump in presence of plasma
Haemolysin
(α,β,γ,δ)Haemolytic dermo-necrotic and leucocidal
Leukocidin
Kills WBCS by producing holes in their CM
Enterotoxin
Act on ANS to cause illness
TSSTsuperantigens
Produce fever, skin rashes,diarrhoea,conjunctivitis,and eath to shock
Exfoliating toxin
Breaks intracellular bridges in the stratum granulosum of epidermis and causes its separation from underlying tissue, resulting in a blistering and exfoliating disease of skin
Free CoagulaseClots plasma by acting along with CRF present in plasma, binding to prothrombin and converting fibrinogen to fibrin
staphylokinase
Degrades fibrin clotsDNAase
Phosphatase
lipase
Phospholipase
Hyaluronidase
Hydrolyze the acidic mucopolyysaccharides present in matrix of connective tisuesHelps to keep
Staphylococcus aureus in the skin for longer period
serokinase
protease
Exam Question
  • Ogston discovered Staphylococcus in 1881
  • Differntiation b/w Staphylococcus aureus & staphylococcus epidermidis can be done by Coagulase, Clumping factor, Heat stable nuclease, Urease, Acid from mannitol ,Acid from trehalose
  • About 30% of general population are healthy nasal carriers
  • Features that Streptococcus shares with staphylococcus are exotoxins and exoenzymes production,Both are Gram-positive cocci,Both cause skin, tissue, and systemic infections Differntiation of streptococcus pyogens with staphylococcus aureus can be done by catalase test
  • An enzyme produced by Staphylococcus aureus that dissolves fibrin clots is staphylokinase
  • Staphylococcus is Gram - positive cocci
  • 3-lactamase production in Staphylococci is under plasmid control
  • Infection by coagulase­ negative Staphylococci are due to Staphylococcus epidermidis
  • S. aureus is Catalase positive, beta-hemolytic staphylococcus species
  • Haemolysin, leukocidin, Enterotoxin, TSST, Exfoliating toxin are the toxins produced by staphylococcus
  • Staphylococcus aureus remains in the skin for longer period because of Hyaluronidase
  • Staphylococcus are Common natural flora of skin
  • Staphylococcus shows Transient colonization
  • For phage typing23 phages of staphylococcus aureus are used
Don't Forget to Solve all the previous Year Question asked on STAPHYLOCOCCI