M. luteus is commonly found on mammalian skin and it is unusual for a member of the natural human flora to degrade urea. It is believed that M. luteus has this ability as an evolutionary hangover from its life in its ancestral soil habitat. In this environment urea is readily available and the ability to degrade it is a distinct advantage. As the species evolved to live on skin the trait remained, as it had no negative effect on survivability.
Micrococcus is a genus within the Micrococcaceae family. With the use of 16s RNA in bacterial taxonomy the genus has recently been revised2. The genus now includes three species, M. luteus, M. lylae and M. antarcticus3. M. luteus is a common yellow gram-positive coccus and roughly 0.5-2.0μm in diameter. Cells appear in pairs, tetrads and irregular clusters but never in chains.4
Method of Isolation
- Isolate a variety of organisms from soil and skin.
By taking samples from four different sources (three skin and one soil) the chance of urea degrading bacteria being present was increased.
- Culture in nutrient broth.
This allowed all isolated microbes to grow.
- Plate sample onto urea plates.
On these plates urea was the only nutrient available, this meant that any bacteria that grew could degrade urea.
Isolated bacteria are grown in a broth containing phosphate buffer, yeast extract, 2% urea and phenol red. An agar slope of the medium is heavily inoculated and incubated at 370c for at least four hours. If the organism only has low urease activity the phosphate buffer will neutralise the NH3 produced. A red colour indicates that NH3 has been produced and the result is positive5.
This is the most important stain in bacteriology and differentiates between gram positive and gram-negative cell walls, which indicates many things about cell structure, and taxonomy. Bacteria isolated from the soil were Gram-positive rods; bacteria isolated from skin were Gram-positive cocci.
- Choose one bacterial species.
The Gram positive cocci found in all three skin samples was selected.
Bacteria contain flavoprotein enzymes that can reduce O2 to H2O2, which is toxic. Catalase is a heme protein that allows the following reaction to occur:
2H2O2→2H2O + O2
The test allows differentiation between lactic acid bacteria and obligate anaerobes, which do not contain catalase from all other bacteria6.
- The results of the above tests placed the bacteria in the family Micrococcaceae.
This tests the ability of the bacteria to move by flagellar rotation through soft agar and reduce tetazolium salts7.
- Perform Hugh and Leifson test.
This test indicates whether the bacterial respiration occurs using the oxidative or fermentative pathway8.
- The results of the above tests placed the bacteria in the genus Micrococcus.
- The results of the above tests and observations showed the bacteria to belong to the species M. luteus
Results
These tests show that the isolated bacteria are Micrococcus able to degrade urea.
Discussion
The ability to degrade urea is no longer of great benefit to any species of Micrococcus although it remains a useful method of distinguishing M. luteus from other species. However, this is not the only test developed for this purpose. Before its revision based on 16s RNA, the Micrococcus genus contained nine species. M. luteus was separated from other species based on the following biochemical tests and their results9.
These tests are now redundant. If analysis of 16s RNA is not done, M. luteus can be distinguished on sight from other Micrococcus as it is now the only yellow species.
References
1.smallfry.dmu.ac.uk/chem./mom/urea/urea.html
2. bergeys 2001
3. chinese Antarctic micrococcus
4 textbook
5.microbial methods pg 54
6.46
7.42
8.37
9.bergeys 1994
