Rhodococcus equi
Mariann Fisher

Rhodococcus equi, also known as Corynebacterium equi, is an intracellular, rod-shaped, gram positive organism with mycolic acid within the cell walls. Two different mycolic acids are seen within this species where they contain a shorter beta-hydroxy chain with a longer alpha-alkyl side chain. This organism is found in soil environments, and is an aerobic, obligate aerobe with mucous and teardrop colonies. It utilizes carbon or carbon and nitrogen sources. This catalase positive organism flourishes in the manure of animals such as; horses, cattle, pigs, and chickens. R. equi is famously known for causing fatal pneumonia which is widespread among breeding farms, especially in foals within the age of six months. It also has been isolated among immune-suppressed humans. This is generally caused by the inhalation of the organism, and a slow spread lung infection that has subtle symptoms such as; decreased appetite, lethargy, fever, chills, and tachypnea. This nonfastidious organism, growing optimally at 30 degrees C, moves to the intestine of the animal where it flourishes and multiplies in fatal levels due to the infection of the normal intestinal flora from birth to twelve weeks. After 12 weeks the bacteria does not multiply in the intestine. R. equi, and its relation to Mycobacterium tuberculosis, is a very infectious and a potentially fatal bacterium.

R. equi was discovered by Magnusson in 1923, from the cause of bronchopneumonia infections amongst horses, colts, sheep, cattle, dogs, goats and swine. The reason why foals are more prone to this organism is unknown, but the animal is not susceptible to this infection after 6 months of age. Although the first human case was a pulmonary infection in 1967, found by Golub, although it did not obtain much clinical importance at that time. In 1986, R. equi became well-known among the AIDS population due to their weaker immune system. To this day between veterinarians and doctors this organism is seen more prevalently.

The treatment of R. equi is expensive and generally unsuccessful. There is no vaccine for this disease, and the symptoms are hard to detect. The treatment is time consuming due to the reoccurring persistence of R. equi. A combination of antibiotics such as; erythromycin and rifampin given orally, proves to be an effective treatment for this organism. Other effective drugs, getamicin or trimethoprim-sulfamethoxazole, are injections. Although these drugs are expensive, there are alternative preventions. The inexpensive approach is for the foals to be born in January when R. equi is frozen within the ground.

Works Cited

http://www.zoologix.com/horse/Datasheets/RhodococcusEqui.htm, Rhodococcus equi

http://medinfo.ufl.edu/year2/mmid/bms5300/bugs/rhoequi.html, Rhodococcus equi

http://www.omafra.gov.on.ca/english/livestock/horses/facts/90-056.htm, Rhodococcus equi Pneumonia Of Foals

http://patients.uptodate.com/topic.asp?file=oth_bact/22311, Rhodococcus equi

*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.


Return to Missouri S&T Microbiology HomePage Go to DJW's HomePage