6 plus species including:



Gram Stain: Gram-positive, non-acid fast.
Morphology: Slender, irregular rods in young cultures, arranged singly or in pairs. Others are arranged at an angle to form "V" formations. In older cultures, rods are shorter and cocci may occur, but a marked rod-coccus cycle does not occur.
Size: 0.4-0.8 micrometers by 1.0-4.0 micrometers.
Motility: Primarily non-motile, but occasionally motility occurs by one to three flagella.
Capsules: None.
Spores: None.
Other: Primary branching is uncommon, but can occur. Mycelia are not produced.


On Yeast Extract-Peptone-Glucose Agar, colonies appear opaque and glistening, often with yellow or orange pigmentation. Other colonies have been noted to appear whitish-yellow to red-orange.



Aerobic; weak anaerobic growth may occur. Chemoorganotrophic. Metabolism is primarily respiratory but may be weakly fermentative. Acid is produced from glucose and other carbohydrates. Nutritional requirements are complex.


M. lacticum has been isolated from milk or dairy sources after laboratory pasteurization or from dairy products that have been heat treated. This species may form a considerable part of the thermoduric bacterial flora of raw and pasteurized milk, powdered milk, cheese and dairy equipment.

M. laevaniformans is reported to occur in raw sewage and in activated sludge. M. imperiale was isolated originally from the alimentary canal of the Imperial moth Eacles imperialis . Bacteria resembling microbacteria have been reported to occur in fresh beef, poultry giblets and raw and pasteurized egg fluid.


Pathogenicity remains allusive. However, foreign body infections and bacteremia have been reported.


For culture: Yeast Extract or Milk Agar.
For selective isolation: Skim Milk or MRS Agar.
For maintenance: Yeast Extract-Peptone Milk for short term maintenance or Lyophilization for long-term preservation.


Temperature: 30-35 degrees C.
Time: 3-4 days.
Atmosphere: Aerobic (weak anaerobic growth may occur).


1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology , Vol. I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Murray, P.R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.

5. Internet: www.hardlink.com /Bacterial Database Search, February, 1998.

6. Hensyl, B.R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

7. Koneman, et al. 1997. Color Atlas and Textbook of Diagnostic Microbiology , 5th ed. Lippincott, Philadelphia, PA.