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Staphylococcus • Family micrococcaeceae • Genus Staphylococcus • 3 important species • 1. Staphylococcus auerus (Coagulase positive ) • 2. Staphylococcus epidermidis CoNS • 3. Staphylococcus saprophyticus (coagulase negative) Microscopical appearance • Gram positive cocci , 1 μm in diameter. arranged clusters (grape like), tetrads, pairs, short chains, non motile, non spore forming mo • o. Culture characteristics • Staphylococci grow readily on most bacteriologic media under aerobic or faculatively anaerobic conditions. • They grow most rapidly at 37 °C but form pigment best at room temperature (20–25 °C). • Colonies on solid media are round, smooth, raised, and glistening. • Staph aureus usually forms gray to deep golden yellow colonies. • Staph epidermidis colonies usually are gray to white On nutrient agar • Staph auerus form golden yellow colonies . Staph epidermidis white colonies on nutrient agar Staph saprophyticus lemon yellow color 50 % produce On blood agar • Staph auerus produce complete haemolysis (clear zone around the growth) • Staph epidermidis • Staph saprophyticus non-haemolytic (no change on blood agar) Staph aureus on blood agar Biochemical activities • Catalase test : all spp of Staphyloccoci give positive catalase which differentiate it from Streptococci (catalase negative). H2O2 catalase H2O + O2 Catalase POS Catalase NEG Staphylococcus Coagulase test • The coagulase test has traditionally been used to differentiate Staphylococcu auerus from coagulase-negative staphylococci . S.aureus produces two forms of coagulase (i.e., bound coagulase and free coagulase). Bound coagulase, otherwise known as "clumping factor", can be detected by carrying out a slide coagulase test, and free coagulase can be detected using a tube coagulase test. Slide coagulase (Bound) causes bacterial cells to agglutinate in the plasma Free coagulase (tube) active enzyme produced by S aureus Fibrinogen Fibrin S. aure us Staphylococcus aureus Coagulase NEG Coagulase POS Growth on mannitol salt agar and mannitol fermentation • MSA is a selective and differential medium in microbiology It encourages the growth of a group of certain bacteria while inhibiting the growth of others. It contains a high concentration (7.5%-10%) of salt (NaCl), making it selective for gram positive bacterium Staphylococci since this level of NaCl is inhibitory to most other bacteria. • It is also a differential medium for mannitol-fermenting staphylococci, containing carbohydrate mannitol and the indicator phenol red a pH indicator for detecting acid produced by mannitol-fermenting Staphylococci. Staphylococcus aureus produce yellow colonies with yellow zones, whereas other Staphylococci produce small pink or red colonies with no colour change to the medium.