Staphylococcus and Micrococcus both are Gram-positive cocci (GPC). Both of these cocci are non-motile, non-sporing, and catalase-positive.
Both of these organisms are normal flora of the skin and mucous membranes of man and animals. Member of the genus Staphylococcus is associated with clinical infections whereas that of Micrococcus is rarely involved in infection.
Some of the notable differences between Micrococcus and Staphylococcus are:
|Morphology||Large Gram-positive cocci, usually arranged in tetrads or in pairs.||Gram-positive cocci in clusters, sometimes in pairs and short chains.|
|Clinical Significance||Usually considered contaminants of clinical specimen; rarely implicated as cause of infections. May cause opportunistic infection in an immunocompromised host.||Bacteria of this genus are of primary clinical significance. S. aureus is a notorious pathogen. S. saprophyticus causes honeymoon cystitis.|
|Lysostaphin Sensitivity Test||Not lysed with lysostaphin (resistant)||Lysed with lysostaphin (sensitive)|
|Furazolidone Sensitivity Test||Resistant to antibiotic furazolidone||Susceptible to antibiotic furazolidone|
|Bacitracin sensitivity test||Susceptible to 0.04 U of bacitracin||Resistant to 0.04 U of bacitracin|
|Microdase Test||Microdase positive||Microdase negative|
|Oxygen requirements||They only grow aerobically (obligate aerobe)||Facultative anaerobic (can use either aerobic respiration and/or fermentation depending on the availability of oxygen, does not solely depend on aerobic respiration for growth).|
|Carbohydrate utilization||Utilize sugars oxidatively or not at all in the O/F test.||Fermentative|
This test is used for the rapid identification of group A streptococci. It can be used to distinguish staphylococci (resistant) from micrococci (sensitive).
- Spread a suspension of the bacterium over a plate of sensitivity test medium.
- Apply a bacitracin disc containing 0.04 units of bacitracin and incubate overnight
- Most staphylococci grow up to the disc or show an inhibition zone less than 10 mm in diameter.
- Micrococci show an inhibition zone generally 10-20 mm in diameter.
B. Lysostaphin Sensitivity
This test distinguishes staphylococci (sensitive) from micrococci (resistant).
Procedure and Result:
- Emulsify the test isolate in 2 ml phosphate-buffered saline at pH 7.3 to a concentration equivalent to McFarland’s opacity standard no. 1.
- Divide the suspension into two portions. To one add a lysostaphin disc and shake vigorously. The other is the control.
- Incubate both portions in a water bath at 37°C for 2 hours.
- Clearing the test suspension relative to the control indicates sensitivity to lysostaphin.