Rhodococcus equi: an animal and human pathogen

Abstract

Recent isolations of Rhodococcus equi from cavitatory pulmonary disease in patients with AIDS have aroused interest among medical microbiologists in this unusual organism. Earlier isolations from humans had also been in immunosuppressed patients following hemolymphatic tumors or renal transplantation. This organism has been recognized for many years as a cause of a serious pyogranulomatous pneumonia of young foals and is occasionally isolated from granulomatous lesions in several other species, in some cases following immunosuppression. The last decade has seen many advances in understanding of the epidemiology, pathogenesis, diagnosis, treatment, and immunity to infection in foals. The particular susceptibility of the foal is not understood but can be explained in part by a combination of heavy challenge through the respiratory route coinciding with declining maternally derived antibody in the absence of fully competent foal cellular immune mechanisms. R. equi is largely a soil organism but is widespread in the feces of herbivores. Its growth in soil is considerably improved by simple nutrients it obtains from herbivore manure. About one-third of human patients who have developed R. equi infections had contact in some way with herbivores or their manure. Others may have acquired infection from contact with soil or wild bird manure. R. equi is an intracellular parasite, which explains the typical pyogranulomatous nature of R. equi infections, the predisposition to infection in human patients with defective cell-mediated immune mechanisms, and the efficacy of antimicrobial drugs that penetrate phagocytic cells.

Rhodococcus equi isolation from sputum of patients with suspected tuberculosis

“…When incubated aerobically at 37°C, R. equi grows efficiently in the majority of nonselective culture media, including media used in mycobacteria isolation and produces irregular, smooth and mucoid colonies that turn a shade of salmon pink to yellow after a week of growth (Prescott 1991 tures in the initial identification of different nocardioform genera (Christopher & Bruno 2002). In general, R. equi is biochemically non-reactive, has no proteolytic activity and fails to oxidize or ferment carbohydrates, with the exception of glucose, which is oxidized by R. equi in 14 days.…”

“…R. equi is strictly aerobic, catalase positive, oxidase negative and mostly urease positive. R. equi produces soluble "equi factors" that are associated with phospholipase and cholesterol oxidase activity and interact with phospholipase D of Listeria ivanovii to induce complete haemolysis of sheep erythrocytes (Prescott 1991).…”

Cloning of a novel ubiquitin‐conjugating enzyme (E2) gene from the ciliate Paramecium tetraurelia

“…Sixteen of the 20 glutamines of this gene were encoded by TAA or TAG. It has been shown that TAA and TAG encode glutamine instead of causing termination in the genes of several ciliates [12]. The predicted UbcP1 protein contains the conserved active site region consensus pattern…”

“…For instance, they have evolved separate somatic and germ-line functions using two distinct nuclei, macro-and micronuclei, respectively [12]. In this respect, they can be used as a model system for multicellular organisms.…”

Genetic Susceptibility to Rhodococcus equi

“…Rhodococcus equi pneumonia is an important disease of foals most commonly characterized by chronic progression associated with development of large pulmonary abscesses 1. Treatment of R. equi pneumonia is prolonged and expensive, and prevention is limited because transfusion of hyperimmune plasma is incompletely effective,2 chemoprophylaxis is inconsistently effective3, 4 and may promote antimicrobial resistance,5 and no effective vaccine is currently available 6.…”