Staphylococcus vs. Micrococcus

Last updated on June 11th, 2021

Staphylococcus in Gram Stain
Staphylococcus in Gram Stain

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:

Characteristics /Tests Micrococcus Staphylococcus
MorphologyLarge Gram positive cocci, usually arranged in tetrads or in pairs.Gram positive cocci in clusters, sometimes in pairs and short chains.
Clinical SignificanceUsually 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 TestNot lysed with lysostaphin  (resistant)Lysed with lysostaphin (sensitive)
Furazolidone Sensitivity TestResistant to antibiotic furazolidoneSusceptible to antibiotic furazolidone
Bacitracin sensitivity testSusceptible to 0.04 U of bacitracinResistant to 0.04 U of bacitracin
Microdase TestMicrodase positiveMicrodase negative
Oxygen requirementsThey 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 utilizationUtilize sugars oxidatively or not at all in the O/F test.Fermentative

A.  Bacitracin Sensitivity

This test is used for the rapid identification of group A streptococci. It can be used to distinguish staphylococci (resistant) from micrococci (sensitive).

Method:

  • 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

Result:

  • 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:

  1. 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.
  2. Divide the suspension into two portions. To one add a lysostaphin disc and shake vigorously. The other is the control.
  3. Incubate both portions in a water bath at 37°C for 2 hours.
  4. Clearing of the test suspension relative to the control indicates sensitivity to lysostaphin.
About Acharya Tankeshwar 474 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.