Gram Stain: Gram-negative.
Morphology: Rods occurring singly or in long, wavy chains or filaments. Some may be highly pleomorphic. Single rods may show central swelling. Chains or filaments may have a series of swellings resulting in a "string of beads" appearance.
Size: 0.1-0.7 micrometers by 1.0-5.0 micrometers with rounded or pointed ends.
Motility: Non-motile.
Capsules: None.
Spores: None.
Other: Fastidious slow-growing organism (asporogenous). Serum ascitic fluid or blood is required for growth. A moist environment or soft agar may enhance growth.


Colonies are small, circular, convex, grayish, smooth, and, glistening. Streptobacillus sometimes exhibits a "fried egg" appearance with a dense center that penetrates agar. Colonies on serum agar are 1-2mm in three days. Colonies on horse or sheep blood agar are non-hemolytic. Serum broth cultures form a white, flocculent sediment at bottom and sides of tubes.



Facultatively anaerobic. Chemoorganotrophic. Ferments glucose and other carbohydrates with acid production, but no gas.


The normal habitat of S. moniliformis is the nasopharynx of laboratory rats and possibly wild rats. The organism is frequently isolated from lesions in laboratory rats having bronchopneumonia, middle ear infections, and conjunctivitis. Reproduction of these diseases in rats by inoculation with S. moniliformis has been unsuccessful.


Human infection with S. moniliformis following rat bite causes one form of rat-bite fever. Human infection following consumption of S. moniliformis contaminated milk is presumed to have been the cause of a disease known as Haverhill fever. Complications of streptobacilliary rat-bite fever may include endocarditis, brain abscesses, amnionitis, as well as bronchitis and pneumonia, abscesses and persistent severe arthritis.

Diseases produced in animals include fatal epizootics on laboratory mice, tendon sheath infection in turkeys, arrested pregnancy and abortion in laboratory mice, cervical abscesses in guinea pigs, and pleuritis in koala bears.


For culture: Tryptose Basal Medium or Meat Broth with added horse serum or defibrinated horse blood.
For selective isolation: None described.
For maintenance: Refrigeration and frequent transferring into broth or agar containing 20% serum is recommended for short-term maintenance. Lyophilization is required for long-term preservation.


Temperature: 35-37 degrees C.
Time: 3 or more days.
Atmosphere: Aerobic with increased CO 2 (5-10%).


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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: /Bacterial Database Search, February, 1998.

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