[Rhodococcus equi--a newly recognized opportunistic pathogen in man].

Abstract

The review informs about substantial features of Rhodococcus equi with emphasis on the analysis of 115 as yet published and still expanding reports on the isolation of this zoopathogenic nocardioform actinomycete from man. Microbiological laboratories of human medicine have to learn not only how to identify R. equi but also recognize it as an opportunistic pathogen in particular in persons with the deficient immunity. R. equi is a gram-positive, encapsulated diphtheroid coccobacillus, partially acid fast. It grows well on common media, its colonies being after 48 hours characteristically mucoid, coalescing, irregular and mostly lightly pinkish. Biochemically it is little active, nevertheless it causes typical synergic haemolysis of erythrocytes influenced by staphylococcal beta-toxin. R. equi is found in soil and manure, especially in horse manure. It causes above all granulomatous pneumonia in young foals. In humans, it causes mostly pneumonia and lung abscess, more frequently in persons with immunity deficiency incl. AIDS, less often extrapulmonary abscesses, sepsis and wound infections. The disease are commonly chronic and recurrent. The ability of R. equi to persist in macrophages and destroy them is important in the pathogenesis of infection. In resistance to infection the cell-mediated immunity seems to be of major importance. The port of entry are the lungs, less often the alimentary tract or injured skin. About a third of the persons gives a history of contact with animals, manure or soil. The standard treatment is prolonged administration of a combination of rifampin and erythromycin. The isolation of R. equi is easy and if a laboratory suspects the presence of this microorganism, its identification is not difficult.