Microbiology Media Growth Patterns Quiz

Growth on Blood Agar Plate

• Staphylococcus grows as creamy white, pinhead colonies with an alpha hemolytic pattern.
• If the petri dish is from the fridge, an alpha prime hemolytic pattern is observed.
• The alpha hemolytic pattern has a small zone of green color inside, surrounded by clearance.
• The beta hemolytic pattern has a large zone of clear color on the outer side.

Growth on Loeffler's Serum Slant

• S. aureus grows as golden yellow.
• S. citreus grows as lemon yellow.
• S. albus (epidermidis) grows as porcelain white.

Growth on Mannitol Salt Agar

• Mannitol is the CHO (carbon source) and phenol red is the pH indicator.
• Inhibitor: 7.5%-10% NaCl.
• S. aureus utilizes carbohydrate and turns yellow.
• S. epidermidis is a non-mannitol fermenter and turns pink.
• S. saprophyticus is variable and may ferment or not ferment.

Catalase Test

• The catalase test is used to differentiate Staphylococcus from Streptococcus.
• Reagent: 3% Hydrogen peroxide (H2O2).
• (+) result: effervescence (bubbles) is observed.
• Staphylococcus is catalase (+), while Streptococcus is catalase (-).

Differentiation of Staphylococcus and Micrococcus

• Micrococcus is differentiated from Staphylococcus using the modified oxidase test (Microdase test).
• Reagent: Tetramethyl-p-phenylenediamine dihydrochloride with Dimethylsulfoxide.
• Negative result: clear.
• Positive result: blue.

Toxins and Enzymes of Staphylococcus

• Protein A: inhibits phagocytosis.
• Coagulase: converts fibrinogen to fibrin clot.
• Staphylokinase (fibrinolysin): capable of producing and dissolving clot.
• Lipase: hydrolyzes lipids.
• Hyalurodinase: capable of hydrolyzing hyaluronic acid in tissue.
• DNAse: degrades DNA.
• Exofoliatins: hydrolyzes tissue through cleavage of stratum granulosum.
• Leukocidins: lyse neutrophil and macrophage.
• Hemolysin: capable of lysing RBC.
• Enterotoxins: cause food poisoning.

Family Streptococcaceae

• Gram-positive, non-motile, non-spore forming, facultative anaerobes.
• Catalase negative.
• Streptococcus is divided into two types of classification: Lancefield and Brown's classification.

Lancefield Classification

• Based on antigenic characteristic of a group-specific cell wall polysaccharide.
• Single Lance group includes many ang.

Brown's Classification

• Based on the pattern of hemolysis.
• More than 20 groups, with the first 4 being clinically significant.

Coagulase Test

• Most important pathogenic determinant of S. aureus.
• Detects cell-bound coagulase (clumping factor).
• Reagent: Rabbit's plasma.
• Alternative reagent: human plasma.
• Rabbit's plasma + inoculum = (+), clumping.
• S. aureus is the only coagulase (+) under Staphylococcus.