Streptobacillus moniliformis
Jim Scott

Streptobacillus moniliformis is a bacterium that is found in many rodents and various mammals. It was first discovered in 1925. S. moniliformis is the cause of a type of illness known as rat-bite fever, it is transmitted to humans who have been bitten or scratched by an infected animal. The bacteria itself is pleomorphic, nonmotile, nonencapsulated, nonsporulating, and is a gram-negative bacillus. The S. moniliformis bacteria is 0.3-0.7 by 1-5 micrometers, and most often occurs in chains and filaments. It is difficult to grow this particular bacteria. It is a facultative anaerobe that is cultured on trypticase soy agar / broth, it has to be supplemented with 10-20% rabbit or horse serum. It is often grown directly in a host.

Streptobacillary rat-bite fever has an initial onset during the 1-22 day incubation period after the initial bite or scratch occurred. The infected patient has an abrupt onset of fever, chills, vomiting, headache, and joint pain. A couple of days after the initial symptoms occur, rashes of tiny pink bumps develop on the palms, soles, and the extremities. Without treatment, the patient risks developing serious infections of the lining of the heart, called endocarditis. Other problems can develop, such as pericarditis, meningitis, or pneumonia. Virtually any tissue or organ in the body may develop a pocket of pus, known as an abscess. These symptoms may relapse irregularly for a period of weeks, months, or years. In many areas of the world, rat-bite fever has a mortality rate of 13%.

Rat-bite fever can be found worldwide. In the North America and South America, it is most often caused by S. moniliformis. In Asia, and most other countries, it is caused by Spirillum minus. Rat-bite fever can be found mostly in Asia, North America, South America, and across Europe. Carriers of S. moniliformis include: rats, weasels, gerbils, turkeys, and anything that preys on these animals. Humans can get it by getting scratched or bit by an infected animal, handling dead animals that carry it, or by eating an infected animal. Lab workers, sewer workers, and people that live in crowded urban areas are at risk of infection.

Diagnosis of the disease is done by taking a sample of blood or fluid from a painful joint. The sample can then be cultured or transferred to a live host to allow the organism to grow. Microscopic examinations should confirm S. moniliformis. Many health-care professionals monitor the patient for a period of time in conjunction with culturing and biochemical testing. Rat-bite fever is often mistaken for many other types of illnesses such as; lyme’s disease, arthritis, syphilis, brucellosis, and rheumatic fever.

It is extremely important to get the proper treatment if infected. Shots of penicillin G or penicillin V taken orally are usually effective against the S. moniliformis bacteria. Erythromycin or tetracycline may be given to patients with allergies to penicillin. Tetanus shots should be given to a bite patient. The bacterium is susceptible to 70% ethanol, 1% sodium hypochlorite, and 2% glutaraldehyde. It inactivates at 121 degrees celcius for 15 minutes.
To prevent infection of S. moniliformis, some preventative measures should be taken. Avoid contact with infected animals capable of transmitting the bacterium. This can often be difficult due to the fact that some economic situations don’t allow for people to move away at will. Another step is to try to eradicate the rats from urban populations. Lab workers are recommended to wear protective gloves when handling animals. Also avoid undercooked food and unpasteurized milk and water.

Reference Sources:

Stanford, Dr. James. Associate Professor of Medicine Division of Infectious Diseases, University of Missouri, Kansas City: Truman Medical Center Hospital-Hill (Lecture Notes)

Madoff, Lawrence C. “Infections from Bites, Scratches, and Burns.” In Harrison’s Principles of Internal Medicine, ed. Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.

Sherris Medical Microbiology: An Introduction to Infectious Diseases. 3rd ed. Ed. Kenneth J Ryan. Norwalk, CT: Appleton & Lange, 1994.

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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