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PubMed1989

Early events associated with experimental infection of the murine lung with Rhodococcus equi.

Pneumonia due to Rhodococcus equi was induced in the murine lung by deposition of a known dose of organisms. From serial estimations of bacterial numbers in the lungs of inoculated mice, analysis of the cellular composition of bronchoalveolar lavage fluid and morphological examination of the lungs, events in the host-parasite interaction were followed until day 7. Early bacterial clearance from the lung was dose-dependent but was not sustained. A proportion of the inoculated R. equi was susceptible to the early nonspecific phagocytic cell response, and the contribution of neutrophils to bacterial clearance appeared largely limited to the first 24 hours. A substantial fraction of the organisms survived in the alveoli, probably within macrophages. The contribution phagocytes make to resistance against R. equi is similar to that which prevails in infection with Listeria monocytogenes.

Actinomycetales Infections↗
PubMed1982

Immunity to and immunotherapy for Rhodococcus equi.

Immune responses to Rhodococcus equi were assayed in mares and foals on 7 studs in south-eastern Australia using skin test reactivity to the intradermal injection of culture filtrate and an indirect fluorescent antibody test. The prevalence of positive skin-test reactions did not differ between studs with a history of R. equi disease and those without but there were more mares with high antibody titres on studs with a disease history. A leucocyte extract prepared from mares that were skin-test positive was evaluated for its ability to protect foals exposed to experimental or natural challenge: 2 foals receiving leucocyte extract became skin-test positive and had resolving lesions present at post-mortem examination. All foals challenged experimentally developed serum antibody but only in those that became skin-test positive were the lesions resolving. In a field trial of leucocyte extract, using 450 foals over 2 foaling seasons, no significant difference was detected in morbidity or mortality rates between treatment and control groups. It is suggested that, since R. equi is so ubiquitous and most horses show immunological evidence of exposure, the development of clinical disease may be related to individual inability to cope with this organism. This may be due to inherited immunological unresponsiveness or to environmental factors which increase the challenge or decrease resistance.

Actinomycetales↗
PubMed2000

Rhodococcus equi and HIV-1 infection in Uganda.

OBJECTIVES: To describe three cases of Rhodococcus equi infection in a cohort of HIV-1 infected adults in Entebbe, Uganda and to compare this to the rates and presentation of tuberculosis in this cohort. METHODS: Consecutive HIV-1 infected adults registering with a community HIV/AIDS clinic in Entebbe were enrolled in a cohort between October 1995 and June 1998 as part of an intervention trial of pneumococcal polysaccharide vaccine. Participants were routinely reviewed every 6 months and had open access to the clinic when unwell. Standard protocols were followed for investigation and management of illness. Microbiological investigations followed standard procedures. RESULTS: 1372 (71% female) study participants were followed for 2141 person years of observation (pyo). Rhodococcus equi was isolated from three study participants from blood, a lymph node aspirate and stool. The individuals were undergoing investigation of acute pneumonia, acute cough with cervical lymphadenopathy and chronic fever with wasting, respectively. The clinical features of these cases are described. All had a CD4 T-cell count of <300/ml. The rate of R. equi infection in the cohort was 1.4/1000 pyo. There were 132 cases of pulmonary and extrapulmonary tuberculosis in the cohort which were diagnosed either microbiologically or clinically. The rate of laboratory confirmed mycobacterial disease was 50.1/1000 pyo. The ratio of mycobacterial disease to R. equi disease was 36:1 (95% CI 11-113:1). CONCLUSIONS: Rhodococcus equi infection occurs in HIV-1 infected adults in Africa. The infection is clinically indistinguishable from pulmonary and extra-pulmonary tuberculosis in the cohort described here. Although the rate of R. equi disease is much less than that of tuberculosis, it is important to consider it in the differential diagnosis of tuberculous infection in cases which are smear negative. Rhodococcus equi infection is probably underdiagnosed in Africa due to a lack of microbiological facilities and its resemblance to common commensal organisms.

AIDS-Related Opportunistic Infections↗
PubMed1994

Effect of growth temperature on maintenance of virulent Rhodococcus equi.

Repeated passage of virulent Rhodococcus equi ATCC 33701 and L1 at 38 degrees C resulted in attenuation of the strains as a result of curing the virulence plasmid; at 30 degrees C, repeated passage had no such effect. At a temperature of 38 degrees C the plasmid-bearing cells replicated more slowly than their plasmid-cured derivatives and so were gradually replaced by cells lacking plasmids. In contrast, at a temperature of 30 degrees C the growth rate of either strain was not affected by the presence or absence of the plasmid. No plasmid-cured derivative was recovered from mouse organs at 48 h after inoculation of a mixture of equal numbers of bacteria with and without plasmids. It is concluded that under nonselective conditions growth temperature is an important factor in maintaining the virulence of R. equi.

Actinomycetales Infections↗
PubMed1996

Relationship between haemagglutination and HeLa-cell adherence of Rhodococcus equi.

In this study, 45 Rhodococcus equi isolates from animals and humans were identified by the Api Coryne system, and serologically with monospecific antisera against capsular types 1-7, with serotypes 1 and 2 predominating. Regardless of serotype, 14 out of 31 isolates from animals and one of 14 isolates from humans expressed 15-17-kD virulence-associated proteins. In hexadecane adherence studies, serotype 2 isolates generally displayed hydrophobic surfaces. In addition, isolates of serotype 1 generally haemagglutinated erythrocytes from rabbits. Neither property appeared to be related to the occurrence of the virulence-associated proteins. By contrast, the haemagglutination reaction correlated significantly with the adherence of the bacteria to HeLa cells. This adhesion might serve as additional marker of virulence among isolates of R. equi and might be useful in epidemiological studies.

Alkanes↗
PubMed2003

Immunoglobulin G subisotype responses of pneumonic and healthy, exposed foals and adult horses to Rhodococcus equi virulence-associated proteins.

Rhodococcus equi causes severe pyogranulomatous pneumonia in foals and in immunocompromised humans. Replication of virulent isolates within macrophages correlates with the presence of a large plasmid which encodes a family of seven virulence-associated proteins (VapA and VapC to VapH), whose functions are unknown. Although cell-mediated immunity is thought to be crucial in eliminating R. equi infection, antibody partially protects foals. The antibody response to both VapA and VapC was similar in six adult horses and six naturally exposed but healthy foals, as well as in eight foals with R. equi pneumonia. The immunoglobulin G (IgG) subisotype response of pneumonic foals to Vap proteins was significantly IgGb biased and also had a trend toward higher IgGT association compared to the isotype association of antibody in adult horses and healthy exposed foals. This suggests that in horses, IgGb and IgGT are Th2 isotypes and IgGa is a Th1 isotype. Furthermore, it suggests that foals which develop R. equi pneumonia have a Th2-biased, ineffective immune response whereas foals which become immune develop a Th1-biased immune response. Pneumonic foals had significantly more antibody to VapD and VapE than did healthy exposed foals. This may indicate a difference in the expression of these two Vap proteins during persistent infection. Alternatively, in pneumonic foals the deviation of the immune response toward VapD and VapE may reflect a bias unfavorable to R. equi resistance. These data indicate possible age-related differences in the equine immune response affecting Th1-Th2 bias as well as antibody specificity bias, which together favor the susceptibility of foals to R. equi pneumonia.

Age Factors↗
PubMed2005

Immune response to vaccines based upon the VapA protein of the horse pathogen, Rhodococcus equi, in a murine model.

Rhodococcus equi is a significant pathogen in foals predominantly causing a pyogranulomatous bronchopneumonia. Many vaccine candidates have been tested for the prevention of R. equi disease in foals. However, none of these have been developed for widespread commercial use. Previous studies have shown that a Th1 immune response is imperative for the protection of foals against R. equi disease. In this study a DNA and a protein vaccine based upon the well-characterised R. equi virulence-associated protein VapA were developed. The vaccines were tested in the BALB/c murine model and the results showed that both vaccine candidates elicited a Th1-type response in the host. Upon coadministration of an IL-12 expression plasmid with the DNA vaccine, an increase in the Th1 response was observed. However, when mice were challenged with 1.5 x 10(7) virulent R. equi ATCC 33701 none of the vaccinated mice showed protection apart from the mice immunised with live R. equi. These results indicate that despite their immunogenicity the VapA-based DNA and recombinant protein vaccines developed in this study were unable to prevent bacterial replication following a high-dose systemic challenge with virulent R. equi in the BALB/c model.

Actinomycetales Infections↗
PubMed1996

Rhodococcus equi: an emerging opportunistic pathogen.

Rhodococcus equi is emerging as a cause of pneumonia in immunocompromised people, especially those with AIDS. Like mycobacteria, R. equi is phagocytosed by alveolar macrophages and replicates within them. Recent work is beginning to elucidate the cell and molecular biology of this opportunistic pathogen and the host immune response to it.

Actinomycetales Infections↗
PubMed1999

Disseminated Rhodococcus equi infection in two goats.

Rhodococcus equi infection was diagnosed in two goats from the same herd. At necropsy, numerous caseating granulomas were disseminated throughout the liver, lungs, abdominal lymph nodes, medulla of right humerus, and the right fifth rib of goat No. 1, and the liver of goat No. 2. Histopathologic examination confirmed the presence of multiple caseating granulomas in these organs. Numerous gram-positive and Giemsa-positive coccobacilli were identified within the cytoplasm of macrophages. Aerobic bacterial cultures of the liver and lung from both goats yielded a pure growth of R. equi. R. equi antigens were immunohistochemically identified in caseating granulomas from both goats. However, the 15- to 17-kd virulence antigens of R. equi were not detected, suggesting possible infection by an avirulent strain of this organism.

Actinomycetales Infections↗
PubMed2005

The iron-regulated iupABC operon is required for saprophytic growth of the intracellular pathogen Rhodococcus equi at low iron concentrations.

Rhodococcus equi is a facultative intracellular pathogen which proliferates rapidly in both manure-enriched soil and alveolar macrophages. Although both environments are characterized by extremely low concentrations of free iron, very little is known regarding the strategies employed by R. equi to thrive under these conditions. This paper reports the characterization of an R. equi transposome mutant that fails to grow at low iron concentrations. The transposome was shown to be inserted into iupA, the first gene of the iupABC operon encoding an ABC transport system highly similar to siderophore uptake systems. Disruption of the iupA gene also resulted in a failure of R. equi to utilize heme and hemoglobin as a source of iron. Introduction of the iupABC operon in trans restored the wild-type phenotype of the mutant strain. iupABC transcripts were 180-fold more abundant in R. equi grown in iron-depleted medium than in organisms grown in iron-replete medium. Proliferation of the iupABC mutant strain in macrophages was comparable to that of the wild-type strain. Furthermore, the iupABC mutant was not attenuated in mice, showing that the iupABC operon is not required for virulence.

ATP-Binding Cassette Transporters↗
PubMed1995

Identification of virulence-associated antigens and plasmids in Rhodococcus equi from patients with AIDS.

Rhodococcus equi is an emerging opportunistic pathogen of human immunodeficiency virus-infected patients. However, little is known about the characteristics of R. equi isolates from humans. This study characterized the plasmid content, expression of a virulence-associated antigen, and mouse virulence of 19 R. equi isolates from patients with and without AIDS. EcoRI digestion patterns and Southern, Western, and virulence analyses of these isolates with cryptic plasmids allowed definition of a new category of R. equi. Isolates from patients with AIDS tended either to be virulent and have 15- to 17-kDa antigens and an 85-kb plasmid (10(6) bacteria needed for lethality) or have intermediate virulence (10(7) bacteria needed for lethality) and one of four distinct large plasmids that share DNA homology and express a 20-kDa antigen. Most of the non-AIDS isolates were avirulent (> 10(8) bacteria needed for lethality) and did not express any of these antigens.

AIDS-Related Opportunistic Infections↗
PubMed1998

Thyroid abscess due to Rhodococcus equi in a patient infected with the human immunodeficiency virus.

A case of thyroid abscess due to Rhodococcus equi in an HIV-positive patient with previous pulmonary abscess is reported. Rhodococcus equi is a gram-positive rod that can cause infections in both immunocompetent and immunocompromised patients, though it occurs more frequently in patients with dysfunctional cellular immune systems. Several cases of Rhodococcus equi infection in persons infected with HIV have been reported. In these patients Rhodococcus equi usually invades the lungs, producing pneumonia. These infections often relapse, accompanied by intermittent bacteremia, despite conventional treatment. Extrapulmonary abscesses can occur.

AIDS-Related Opportunistic Infections↗
PubMed1999

[Equine Rhodococcus equi pneumonia: first report in Israel and its significance for man].

Rhodococcus equi is an important pathogen in young horses. In recent years it has been increasingly recognized as an opportunistic infectious agent in patients with immune deficiency. The increase in recognized cases may be related to the increased prevalence of AIDS. However, more cases may have been recognized lately due to increased awareness of the pathogenicity of this bacterium. Based on medical reports, there appears to be an association between Rhodococcus equi infections and exposure to animals, horses in particular. During the past year, 2 cases of rhodococcus pneumonia were diagnosed in foals in Israel. This information deserves the attention of the local medical community because of the zoonotic potential of Rhodococcus equi and the danger of its becoming more common. The climate in Israel is conducive to its growth and viability and since it flourishes in an environment with horses, the significant growth in our equine industry in recent years may contribute to an increase in Rhodococcus infections.

Actinomycetales Infections↗
PubMed1999

[Pulmonary malacoplakia caused by Rhodococcus equi in AIDS: a case report].

We describe the observation of a right upper lobe consolidation with cavitation produced by Rhodococcus equi in a patient suffering from AIDS. The inefficacy of a prolonged antimicrobial therapy adapted against R. equi led to a right upper lobectomy. The histopathology showed a pseudotumoral mass, with dense infiltration of macrophages containing Michaelis-Gutmann bodies, which was positive for the culture of R. equi. Pulmonary malacoplakia with Rhodococcus equi was diagnosed. This pathology should be evoked when a R. equi pneumonia persists despite a right management of treatment for several months. The features of pneumonia with Rhodococcus equi and of pulmonary malacoplakia are taken from a literature review.

AIDS-Related Opportunistic Infections↗
PubMed1984

Ecology of Rhodococcus equi.

A selective broth enrichment technique was used to study the distribution of Rhodococcus equi in soil and grazing animals. Rhodococcus equi was isolated from 54% of soils examined and from the gut contents, rectal faeces and dung of all grazing herbivorous species examined. Rhodococcus equi was not isolated from the faeces or dung of penned animals which did not have access to grazing. The isolation rate from dung was much higher than from other samples and this was found to be due to the ability of R. equi to multiply more readily in dung. Delayed hypersensitivity tests were carried out on horses, sheep and cattle, but only horses reacted significantly. The physiological characteristics of R. equi and the nature of its distribution in the environment suggested that R. equi is a soil organism.

Actinomycetales↗
PubMed1999

[Pulmonary infection from Rhodococcus equi after renal transplantation. Review of the literature].

Rhodococcus Equi, a strictly aerobic Gram positive coco-bacillus, is a pathogen for horses and foals. It may induce opportunistic infections and is described in AIDS infected patients. We report the case of a 47-year old man, breeder of horses, with kidney transplant who has presented, 8 years after his graft, an impairment of health, a fever and evidence of pulmonary disease. The pulmonary biopsy under scanner guidance and microbiology study, has displayed the diagnosis of Rhodococcus equi infection. The evolution has been favorable with double antibiotherapy (follow-up 27 months). Ten comparable observations have been published after organ transplantation: (kidney: 8; heart: 1; liver: 1). Pulmonary locations are widely predominant. The animal contact is found only in 30% of cases. The presentation of the sickness has been compared to pulmonary tuberculosis or to nocardiosis, pathologies often observed in this context of immunosuppression. The antibiotic treatment is difficult and should required two bactericidal antibiotics. A surgical lobectomy can be envisaged in case of relapse. The mortality is 30%.

Actinomycetales Infections↗
PubMed2004

Rapid determination of vapA/vapB genotype in Rhodococcus equi using a differential polymerase chain reaction method.

Rhodococcus equi is a facultative pathogen of foals. Infection causes an often fatal pulmonary pneumonia. The organism has also been isolated from pigs, cattle, humans and the environment. Equine virulence has a high positive correlation with the expression of a 17.4 kD polypeptide of unknown function, VapA, the product of the plasmid-encoded vapA gene. More recently an isogene of vapA, referred to as vapB and encoding an 18.2 kDa polypeptide, has been identified among pig and human isolates. The two genes share > 80% sequence identity, yet their host strains apparently exhibit different pathogenicity profiles (for example by reference to virulence in mouse model system and host specificity). In this study, a polymerase chain reaction (PCR) technique was developed that permits the selective amplification of vapA and vapB. Using this technique the distribution of the two genes among 35 randomly selected isolates of Rhodococcus equi from various animal and environmental sources was determined. Using this technique the genotype of each isolate could be unambiguously assigned as vapA+, vapB+ or vap- (i.e., scoring negative for both vapA and vapB). No isolate scored positive for both vapA and vapB. 100% of equine isolates scored vapA+, confirming the status of vapA as a reliable marker of equine virulence. All three genotypes were found among human isolates; porcine isolates scored either vapB+ or vap- and no vapA+ isolates were present in this sample. Rigorous statistical analysis using the Fisher Exact test confirmed that the high frequency of vapA+ among equine isolates is significant; however the sample size was too small to draw statistically significant conclusions regarding the distribution of genotypes among within other animal groups.

Actinomycetales Infections↗