Rhodococcus equi infection in HIV-positive subjects: a retrospective analysis of 24 cases

Metagenomic next-generation sequencing for rapid detection of pulmonary infection in patients with acquired immunodeficiency syndrome

BACKGROUND

Acquired immunodeficiency syndrome (AIDS) is associated with a high rate of pulmonary infections (bacteria, fungi, and viruses). To overcome the low sensitivity and long turnaround time of traditional laboratory-based diagnostic strategies, we adopted metagenomic next-generation sequencing (mNGS) technology to identify and classify pathogens.

RESULTS

This study enrolled 75 patients with AIDS and suspected pulmonary infections who were admitted to Nanning Fourth People's Hospital. Specimens were collected for traditional microbiological testing and mNGS-based diagnosis. The diagnostic yields of the two methods were compared to evaluate the diagnostic value (detection rate and turn around time) of mNGS for infections with unknown causative agent. Accordingly, 22 cases (29.3%) had a positive culture and 70 (93.3%) had positive valve mNGS results (P value < 0.0001, Chi-square test). Meanwhile, 15 patients with AIDS showed concordant results between the culture and mNGS, whereas only one 1 patient showed concordant results between Giemsa-stained smear screening and mNGS. In addition, mNGS identified multiple microbial infections (at least three pathogens) in almost 60.0% of patients with AIDS. More importantly, mNGS was able to detect a large variety of pathogens from patient tissue displaying potential infection and colonization, while culture results remained negative. There were 18 members of pathogens which were consistently detected in patients with and without AIDS.

CONCLUSIONS

In conclusion, mNGS analysis provides fast and precise pathogen detection and identification, contributing substantially to the accurate diagnosis, real-time monitoring, and treatment appropriateness of pulmonary infection in patients with AIDS.

Nadir Bir Etken: Rhodococcus equi, İmmunkompetan Hastalarda Yumuşak Doku Enfeksiyonlarına İlişkin Bir Vaka Sunumu ve Literatür İncelemesi

Rhodococcus equi is a microorganism that was first described in horses and later it had been found out to cause opportunistic infections in immunosuppressed patients. It causes especially pulmonary infections in immunocompromised patients while it rarely causes diseases such as septic arthritis and soft tissue infections. It is important to question epidemiological risk factors for the diagnosis of the disease. Also the clinician-microbiologist relationship is important in the laboratory diagnosis of the microorganism because it is possible to be missed as the part of normal flora or contaminant or to be confused with microorganisms with similar phenotypic features (Nocardia species or rapidly growing mycobacteria). Rarely, it has been reported in immunocompetent patients, as in our case. MEDLINE, SCOPUS, Google Scholar, and Cochrane searches were performed using keywords Rhodococcus equi and Corynebacterium equi from 1945 to July 2021. A total of 582 articles were determined. Articles containing these keywords were then scanned for words "humans", “soft tissue infections”, and “cellulite” and a total of 42 articles were listed in the end. A total of 14 case reports of soft tissue infection/cellulitis in immunocompetent patients related R. equi were detected in the literature In our case, there was a soft tissue infection and R. equi was detected in the abscess culture. Obtaining culture and determining the factor is very important in the treatment of infections. In this report, soft tissue infections caused by R. equi in immunocompetent patients are reviewed.

Pangenomic and functional investigations for dormancy and biodegradation features of an organic pollutant-degrading bacterium Rhodococcus biphenylivorans TG9

Environmental bacteria contain a wealth of untapped potential in the form of biodegradative genes. Leveraging this potential can often be confounded by a lack of understanding of fundamental survival strategies, like dormancy, for environmental stress. Investigating bacterial dormancy-to-degradation relationships enables improvement of bioremediation. Here, we couple genomic and functional assessment to provide context for key attributes of the organic pollutant-degrading strain Rhodococcus biphenylivorans TG9. Whole genome sequencing, pangenome analysis and functional characterization were performed to elucidate important genes and gene products, including antimicrobial resistance, dormancy, and degradation. Rhodococcus as a genus has strong potential for degradation and dormancy, which we demonstrate using R. biphenylivorans TG9 as a model. We identified four Resuscitation-promoting factor (Rpf) encoding genes in TG9 involved in dormancy and resuscitation. We demonstrate that R. biphenylivorans TG9 grows on fourteen typical organic pollutants, and exhibits a robust ability to degrade biphenyl and several congeners of polychlorinated biphenyls. We further induced TG9 into a dormant state and demonstrated pronounced differences in morphology and activity. Together, these results expand our understanding of the genus Rhodococcus and the relationship between dormancy and biodegradation in the presence of environmental stressors.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): antimicrobial-resistant Rhodococcus equi in horses

Rhodococcus equi (R. equi) was identified among the most relevant antimicrobial-resistant (AMR) bacteria in the EU for horses in a previous scientific opinion. Thus, it has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on its eligibility to be listed, Annex IV for its categorisation according to disease prevention and control rules as in Article 9 and Article 8 for listing animal species related to the bacterium. The assessment has been performed following a methodology previously published. The outcome is the median of the probability ranges provided by the experts, which indicates whether each criterion is fulfilled (lower bound ≥ 66%) or not (upper bound ≤ 33%), or whether there is uncertainty about fulfilment. Reasoning points are reported for criteria with uncertain outcome. According to the assessment here performed, it is uncertain whether AMR R. equi can be considered eligible to be listed for Union intervention according to Article 5 of the AHL (10-66% probability). According to the criteria in Annex IV, for the purpose of categorisation related to the level of prevention and control as in Article 9 of the AHL, the AHAW Panel concluded that the bacterium does not meet the criteria in Sections 1 and 2 (Categories A and B; 5-10% and 10-33% probability of meeting the criteria, respectively), and the AHAW Panel is uncertain whether it meets the criteria in Sections 3, 4 and 5 (Categories C, D and E; 10-66% probability of meeting the criteria in all three categories). The animal species to be listed for AMR R. equi according to Article 8 criteria are mainly horses and other species belonging to the Perissodactyla and Artiodactyla orders.

Rhodococcus equi infection: A diverse spectrum of disease

Rhodococcus equi is a gram positive bacterium most commonly presenting clinically as pneumonia, however can disseminate to cause disease in virtually any human tissue. Although it is predominantly an opportunistic pathogen, a number of case series have described infection occurring among individuals with a normal immune system. We describe two cases of Rhodococcus equi infection which highlight the diversity of disease presentations of this rare organism.

Chronic cavitary pneumonia by Rhodococcus equi in a highly prevalent tuberculosis country: a diagnosis challenge

Rhodococcus equi is a facultative aerobic, intracellular, non-motile, non-spore-forming, Gram-positive, weakly acid-fast coccobacillus belonging to the group of nocardioform actinomycetes. R. equi infections are rare opportunistic illnesses in patients with Acquired Immunodeficiency Syndrome (AIDS), associated with a high mortality rate. The most common clinical presentation of R. equi infections is a chronic cavitary pneumonia. Due to its acid-fastness, R. equi can be mistaken for others acid-fast organisms, as Mycobacterium tuberculosis. In turn, R. equi is also a gram-positive pleomorphic bacteria and can be mistaken for diphtheroids or Micrococcus organisms, being accidentally disregarded as oral contaminants in sputum cultures. Therefore, in Brazil, a highly prevalent tuberculosis (TB) country, pulmonary infections caused by R. equi may mimic pulmonary TB and represent a diagnostic challenge. Here, we report on a case of chronic cavitary pneumonia by R. equi in a Human Immunodeficiency Virus (HIV)-infected patient, focusing on diagnostic aspects.

Rhodococcus equi Pneumonia in Kidney Transplant Recipient Affected by Acute Intermittent Porphyria: A Case Report

Rhodococcus equi is a gram-positive coccobacillus responsible for severe infections in patients with weakened immune systems. R equi generally causes pnumonia that may evolve into fatal systemic infection if left untreated. Here, we present a case of a 67-year-old woman affected by acute intermittent porphyria (AIP) who developed R equi pneumonia 7 months after kidney transplantation. Although clinical features at presentation were nonspecific, lung computed tomography showed right perihilar consolidation with a mass-like appearance causing bronchial obstruction. Appropriate antibiotic including intravenous meropenem and oral azithromycin that was then switched to oral levofloxacin and oral azithromycin along with reduction of immunosuppressive therapy resolved pneumonia without provoking an acute attack of porphyria. AIP limited the choice of antibiotics for the treatment of R equi infection because some potentially porphyrinogenic antibacterial agents were avoided. Based on this experience, azithromycin and meropenem can be safely administered for the treatment of R Equi infection in patients with AIP.

Diagnosis and management of pulmonary infection due to Rhodococcus equi

BACKGROUND

Rhodococcus equi is a recognized cause of disease in humans, especially in individuals who are immunocompromised. Because diphtheroids are regarded as part of normal respiratory flora, the importance of R. equi as a pulmonary pathogen may not be fully appreciated and its prevalence may be underestimated. Most treatment recommendations for R. equi infection were established before antiretroviral drugs became available for human immunodeficiency virus/AIDS therapy, and therapeutic strategies may need to be updated.

OBJECTIVES

To review the role of R. equi as a cause of pulmonary infection; to highlight its importance for clinicians and microbiologists; and to challenge current approaches to treatment, whether in immunodeficient or immunocompetent individuals.

SOURCES

A PubMed search using combinations of the following terms: 'Rhodococcus (automatically including Corynebacterium) equi' AND 'pneumonia' OR 'pulmonary' infection, then cross-checking references in the resulting cases, case series and reviews.

CONTENT

We provide a review that details the challenges in the diagnosis, microbiology and pathogenesis of pulmonary infection caused by R. equi and the options for treatment.

IMPLICATIONS

Ten to 14 days of treatment may be effective for pneumonia due to R. equi. Our review suggests that longer courses of therapy are needed for cavitary lesions and lung masses. However, recommendations for excessively prolonged treatment of all pulmonary infections arose during a time when many cases occurred in individuals with AIDS and before effective antiretroviral therapy was available. We suggest that the rationale for prolonged therapy with multiple antibiotics needs to be re-evaluated.

Development of septic polysynovitis and uveitis in foals experimentally infected with Rhodococcus equi

Rhodococcus equi is one of the most important causes of disease in foals. Infection is typically characterized by pyogranulomatous pneumonia although extrapulmonary infections occur occasionally. Uveitis and polysynovitis have been reported in foals naturally infected with R. equi and are thought to be the result of an immune-mediated process. However, the pathogenesis of these conditions is poorly understood. The objectives of this study were to document the occurrence of uveitis and polysynovitis after experimental infection with R. equi and to determine if these disorders are the direct result of infection at these sites. Foals between 3 and 4 weeks of age were infected intratracheally with virulent R. equi using inocula of 1×10⁸ CFU (high inoculum; n = 16) or 1×10⁷ CFU (low inoculum; n = 12). Foals were monitored twice daily and necropsy was performed 14 days post-infection. Aqueous humor and synovial fluid were collected aseptically and the percentage of affected lung was calculated. The mean (± SD) percentage of affected lung was significantly higher with the high inoculum (31.8 ± 14.6%) than with the low inoculum (14.4 ± 11.4%). Fourteen of 25 foals developed uveitis and 20 of 28 foals developed polysynovitis. R. equi was cultured from the aqueous humor of 11 foals and from the synovial fluid of 14 foals. The risk of development of polysynovitis and protein concentration in the aqueous humor were significantly higher in foals that received the high inoculum. These results indicate that polysynovitis and uveitis are septic complications associated with the severity of lung disease.

Effects of priming with cytokines on intracellular survival and replication of Rhodococcus equi in equine macrophages

Rhodococcus equi is a common cause of pneumonia in foals and an opportunistic pathogen in immunosuppressed people. The ability of R. equi to survive and replicate in macrophages is the basis of its pathogenicity. Limited knowledge about the role of cytokines in host defense against R. equi comes from studies in mice and the role of cytokines in intracellular survival of R. equi in equine macrophages is unknown. The objectives of this study were to determine the effect of priming with interferon (IFN)-γ, interleukin (IL)-1β, IL-4, IL-6, IL-10, or tumor necrosis factor (TNF)-α at various concentrations on intracellular survival of virulent R. equi in equine monocyte-derived macrophages (MDM), and to determine the effects of various combinations of the same cytokines on intracellular survival of R. equi. MDM from 10 adult horses were primed with recombinant equine cytokines at doubling concentrations ranging from 25 to 200 ng/mL prior to infection with virulent R. equi. Priming with IFN-γ, TNF-α, or IL-6 significantly decreased intracellular replication of R. equi compared to unprimed monolayers. In contrast, priming with IL-10 or IL-1β significantly increased intracellular replication of R. equi. Pairwise combinations of the cytokines listed above did not results in synergism or antagonism. This study demonstrated that IFN-γ, TNF-α, or IL-6 improved equine MDM function against R. equi whereas IL-1β or IL-10 were detrimental.

Antimicrobial Resistance in Rhodococcus equi

Pneumonia caused by Rhodococcus equi remains an important cause of disease and death in foals. The combination of a macrolide (erythromycin, azithromycin, or clarithromycin) with rifampin has been the recommended treatment for foals with clinical signs of infection caused by R. equi since the early 1980s with, until recently, only rare reports of resistance. Resistance to macrolides and rifampin in isolates of R. equi cultured from horses is increasing, with isolates resistant to all macrolides and rifampin now being cultured from up to 40% of infected foals at some farms. This text reviews the available data regarding antimicrobial resistance in R. equi , with emphasis on the molecular mechanisms of the recent emergence of resistance to macrolides and rifampin in equine isolates of R. equi .

Differences in Rhodococcus equi Infections Based on Immune Status and Antibiotic Susceptibility of Clinical Isolates in a Case Series of 12 Patients and Cases in the Literature

Rhodococcus equi is an unusual zoonotic pathogen that can cause life-threatening diseases in susceptible hosts. Twelve patients with R. equi infection in Kentucky were compared to 137 cases reported in the literature. Although lungs were the primary sites of infection in immunocompromised patients, extrapulmonary involvement only was more common in immunocompetent patients (P < 0.0001). Mortality in R. equi-infected HIV patients was lower in the HAART era (8%) than in pre-HAART era (56%) (P < 0.0001), suggesting that HAART improves prognosis in these patients. Most (85–100%) of clinical isolates were susceptible to vancomycin, clarithromycin, rifampin, aminoglycosides, ciprofloxacin, and imipenem. Interestingly, there was a marked difference in susceptibility of the isolates to cotrimoxazole between Europe (35/76) and the US (15/15) (P < 0.0001). Empiric treatment of R. equi infection should include a combination of two antibiotics, preferably selected from vancomycin, imipenem, clarithromycin/azithromycin, ciprofloxacin, rifampin, or cotrimoxazole. Local antibiograms should be checked prior to using cotrimoxazole due to developing resistance.

Biofilm formation by Rhodococcus equi and putative association with macrolide resistance

Abstract: Rhodococcus equi is a facultative intracellular pathogen, which cause severe pyogranulomatous pneumonia in foals and tuberculosis-like lesions in humans. Its ability to form biofilm was described in strains isolated from chronic diseases associated to treatment failures in humans. This study aimed to verify the biofilm formation by 113 R. equi isolated from equine samples (clinical and fecal) using two different methods (biofilm-culturing with and without additional glucose and epifluorescence microscopy). We also aimed to determine the efficacy of azithromycin, clarithromycin and erythromycin on R. equi in established biofilm. We found 80.5% (26/41) and 63% (58/72) biofilm-positive isolates, in fecal and clinical samples, respectively. The additional glucose increased the biofilm formation by R. equi fecal samples, but not by clinical samples. The antimicrobials tested herein were not able to eradicate R. equi in biofilm even at higher concentrations. This is the first study showing the biofilm formation by R. equi isolated from equine samples. Our findings indicate that R. equi biofilm-producers may be more resistant to the antimicrobials evaluated. Further studies are warranted to test this hypothesis.

Activity of clarithromycin or rifampin alone or in combination against experimental Rhodococcus equi infection in mice

Treatment of mice with the combination of clarithromycin with rifampin resulted in a significantly lower number of Rhodococcus equi CFU in the organs of mice than treatment with either drug alone or placebo. There was no significant difference in the number of R. equi CFU between mice treated with clarithromycin monotherapy, rifampin monotherapy, or placebo. The combination of clarithromycin with rifampin conferred a clear advantage over either drug as monotherapy in this model of chronic R. equi infection.

Diagnosing Rhodococcus equi infections in a setting where tuberculosis is highly endemic: a double challenge

Rhodococcus equi infection is increasing in regions with high HIV prevalence worldwide. The microbiological features and clinical mimicry of tuberculosis infection pose diagnostic challenges in high-tuberculosis-incidence settings. We present two HIV-associated cases of R. equi infection from Vietnam and discuss the unique diagnostic challenges in such settings.

Comparison of Etest, disk diffusion, and broth macrodilution for in vitro susceptibility testing of Rhodococcus equi

MICs of erythromycin, clarithromycin, azithromycin, rifampin, gentamicin, and doxycycline against 101 isolates of Rhodococcus equi were determined by broth macrodilution, disk diffusion, and Etest. Categorical agreement ranged between 85.1 and 100%. Overall, the agreement between Etest and disk diffusion was better than the agreement between broth macrodilution and the agar-based methods.

Effects of age and macrophage lineage on intracellular survival and cytokine induction after infection with Rhodococcus equi

Rhodococcus equi, a facultative intracellular pathogen of macrophages, causes life-threatening pneumonia in foals and in people with underlying immune deficiencies. As a basis for this study, we hypothesized that macrophage lineage and age would affect intracellular survival of R. equi and cytokine induction after infection. Monocyte-derived and bronchoalveolar macrophages from 10 adult horses and from 10 foals (sampled at 1-3 days, 2 weeks, 1 month, 3 months, and 5 months of age) were infected ex vivo with virulent R. equi. Intracellular R. equi were quantified and mRNA expression of IL-1β, IL-4, IL-6, IL-8, IL-10, IL-12 p40, IL-18, IFN-γ, and TNF-α was measured. Intracellular replication of R. equi was significantly (P<0.001) greater in bronchoalveolar than in monocyte-derived macrophages, regardless of age. Regardless of the macrophage lineage, replication of R. equi was significantly (P=0.002) higher in 3-month-old foals than in 3-day old foals, 2-week-old foals, 1-month-old foals, and adult horses. Expression of IL-4 mRNA was significantly higher in monocyte-derived macrophages whereas expression of IL-6, IL-18, and TNF-α was significantly higher in bronchoalveolar macrophages. Induction of IL-1β, IL-10, IL-12 p40, and IL-8 mRNA in bronchoalveolar macrophages of 1-3-day old foals was significantly higher than in older foals or adult horses. Preferential intracellular survival of R. equi in bronchoalveolar macrophages of juvenile horses may play a role in the pulmonary tropism of the pathogen and in the window of age susceptibility to infection.

Rhodococcus equi: the many facets of a pathogenic actinomycete

Rhodococcus equi is a soil-dwelling pathogenic actinomycete that causes pulmonary and extrapulmonary pyogranulomatous infections in a variety of animal species and people. Young foals are particularly susceptible and develop a life-threatening pneumonic disease that is endemic at many horse-breeding farms worldwide. R. equi is a facultative intracellular parasite of macrophages that replicates within a modified phagocytic vacuole. Its pathogenicity depends on a virulence plasmid that promotes intracellular survival by preventing phagosome-lysosome fusion. Species-specific tropism of R. equi for horses, pigs and cattle appears to be determined by host-adapted virulence plasmid types. Molecular epidemiological studies of these plasmids suggest that human R. equi infection is zoonotic. Analysis of the recently determined R. equi genome sequence has identified additional virulence determinants on the bacterial chromosome. This review summarizes our current understanding of the clinical aspects, biology, pathogenesis and immunity of this fascinating microbe with plasmid-governed infectivity.

Other HIV-associated pneumonias

The incidence, mortality, and epidemiology of human immunodeficiency virus (HIV)-associated pulmonary infections have changed as a result of effective antiretroviral and prophylaxis antimicrobial therapy. The clinical presentation, radiographic abnormalities, and treatment of pneumonia from various uncommon pathogens in patients with AIDS can be different from those in immunocompetent patients. Advances in invasive and noninvasive testing and molecular biological techniques have improved the diagnosis and prognosis of pulmonary infections in patients infected with HIV. This review focuses on pulmonary infections from nontuberculosis mycobacteria, cytomegalovirus, fungi (aspergillosis, cryptococcosis, endemic fungi), and parasites (toxoplasmosis), and uncommon bacterial pneumonia (nocardiosis, rhodococcosis) in these patients.

A 39-year-old man with fevers, cough, and right upper lobe cavitory lesion in lung

In this case report, we present a patient who had an endobronchial lesion that was found to be caused by Rhodococcus equi, earlier known as corynebacterium. Although this organism has been reported to infect immunocompromised patients, including several patients with acquired immune deficiency syndrome, it has rarely been reported to present as an endobronchial lesion.

[Bacterial pneumonia in HIV-infected patients (excluding mycobacterial infection)]

Respiratory infections are the most common complications in HIV patients, regardless of the degree of immunosuppression. Even though antiretroviral therapy has a protective effect on the risk of bacterial pneumonia, this still remains high (including those with CD(4)>500/mm(3)). The most frequently isolated bacteria are Streptococcus pneumoniae and Haemophilus influenzae. The clinical and radiological presentations of lower respiratory tract infections in HIV patients are quite variable. The clinical presentation is more severe and the radiological presentation is more atypical if the immunosuppression is severe. The first-line antibiotic therapy is an injectable third-generation cephalosporin (ceftriaxone or cefotaxime) or co-amoxiclav. Pneumococcal vaccination (as well as influenza vaccine) is recommended. Although rare, Nocardia spp. and Rhodococcus equi seem more common among AIDS patients.

Disseminated Rhodococcus equi infection in HIV infection despite highly active antiretroviral therapy

BACKGROUND

Rhodococcus equi (R.equi) is an acid fast, GRAM + coccobacillus, which is widespread in the soil and causes pulmonary and extrapulmonary infections in immunocompromised people. In the context of HIV infection, R.equi infection (rhodococcosis) is regarded as an opportunistic disease, and its outcome is influenced by highly active antiretroviral therapy (HAART).

CASE PRESENTATION

We report two cases of HIV-related rhodococcosis that disseminated despite suppressive HAART and anti-rhodococcal treatment; in both cases there was no immunological recovery, with CD4+ cells count below 200/μL. In the first case, pulmonary rhodococcosis presented 6 months after initiation of HAART, and was followed by an extracerebral intracranial and a cerebral rhodococcal abscess 1 and 8 months, respectively, after onset of pulmonary infection. The second case was characterized by a protracted course with spread of infection to various organs, including subcutaneous tissue, skin, colon and other intra-abdominal tissues, and central nervous system; the spread started 4 years after clinical resolution of a first pulmonary manifestation and progressed over a period of 2 years.

CONCLUSIONS

Our report highlights the importance of an effective immune recovery, despite fully suppressive HAART, along with anti-rhodococcal therapy, in order to clear rhodococcal infection.

Characterization of the role of the pathogenicity island and vapG in the virulence of the intracellular actinomycete pathogen Rhodococcus equi

Rhodococcus equi, a facultative intracellular pathogen of macrophages, causes severe, life-threatening pneumonia in young foals and in people with underlying immune deficiencies. R. equi virulence is dependent on the presence of a large virulence plasmid that houses a pathogenicity island (PAI) encoding a novel family of surface-localized and secreted proteins of largely unknown function termed the virulence-associated proteins (VapACDEFGHI). To date, vapA and its positive regulators virR and orf8 are the only experimentally established virulence genes residing on the virulence plasmid. In this study, a PAI deletion mutant was constructed and, as anticipated, was attenuated for growth both in macrophages and in mice due to the absence of vapA expression. Expression of vapA in the PAI mutant from a constitutive promoter, thereby eliminating the requirement for the PAI-encoded vapA regulators, resulted in delayed bacterial clearance in vivo, yet full virulence was not restored, indicating that additional virulence genes are indeed located within the deleted pathogenicity island region. Based on previous reports demonstrating that the PAI-carried gene vapG is highly upregulated in macrophages and in the lungs of R. equi-infected foals, we hypothesized that vapG could be an important virulence factor. However, analysis of a marked vapG deletion mutant determined the gene to be dispensable for growth in macrophages and in vivo in mice.

Rhodococcus equi infection in HIV-infected individuals: case reports and review of the literature

Rhodococcus equi is a gram-positive, coryneform bacterium that causes zoonotic infection mainly in horses and foals. It sometimes affects humans presenting as cavitary pneumonia. Immunocompromised patients, including HIV-infected patients, are more susceptible to R. equi infection. We present 10 cases of R. equi infection in HIV-positive patients admitted to our institute from 1991 to June 2008. Moreover, we have reviewed 272 cases of R. equi infection in HIV-infected persons, published from 1986 through 2008. With respect to the literature data, the R. equi strains isolated in our case series showed lower sensitivity to ceftriaxone, amoxicillin/clavulanic acid, and cotrimoxazole. Prompt diagnosis, early initiation of antiretroviral treatment and combined antimicrobial treatment seem to be effective to eradicate the infection and to improve the outcome.

Experimental infection of neonatal foals with Rhodococcus equi triggers adult-like gamma interferon induction

Rhodococcus equi is a facultative intracellular pathogen that causes pneumonia in young foals but does not induce disease in immunocompetent adult horses. Clearance of R. equi depends mainly on gamma interferon (IFN-gamma) production by T lymphocytes, whereas the predominance of interleukin 4 (IL-4) is detrimental. Young foals, like neonates of many other species, are generally deficient in the ability to produce IFN-gamma. The objective of this study was to compare the cytokine profiles, as well as cell-mediated and antibody responses, of young foals to those of adult horses following intrabronchial challenge with R. equi. The lymphoproliferative responses of bronchial lymph node (BLN) cells to concanavalin A were significantly higher in foals than in adult horses. In contrast, adult horses had significantly higher lymphoproliferative responses to R. equi antigens than did foals. Infected foals had significantly lower IL-4 mRNA expression but significantly higher IFN-gamma expression and IFN-gamma/IL-4 ratio in R. equi-stimulated BLN lymphocytes than did infected adults. Infection with R. equi in foals resulted in a significant increase in the percentage of T lymphocytes and CD4(+) T lymphocytes in bronchoalveolar lavage fluid in association with a significant decrease in the percentage of these cell populations in BLNs. Infection of foals also resulted in a marked increase in serum immunoglobulin Ga (IgGa) and IgGb levels, resulting in concentrations in serum that were significantly higher than those of adult horses. This study demonstrates that the immune response to R. equi in foals is not biased toward IL-4 and is characterized by the predominant induction of IFN-gamma.

In vivo expression of and cell-mediated immune responses to the plasmid-encoded virulence-associated proteins of Rhodococcus equi in foals

Rhodococcus equi is a facultative intracellular pathogen that causes pneumonia in foals but does not induce disease in adult horses. Virulence of R. equi depends on the presence of a large plasmid, which encodes a family of seven virulence-associated proteins (VapA and VapC to VapH). Eradication of R. equi from the lungs depends on gamma interferon (IFN-gamma) production by T lymphocytes. The objectives of the present study were to determine the relative in vivo expression of the vap genes of R. equi in the lungs of infected foals, to determine the recall response of bronchial lymph node (BLN) lymphocytes from foals and adult horses to each of the Vap proteins, and to compare the cytokine profiles of proliferating lymphocytes between foals and adult horses. vapA, vapD, and vapG were preferentially expressed in the lungs of infected foals, and expression of these genes in the lungs was significantly (P < 0.05) higher than that achieved during in vitro growth. VapA and VapC induced the strongest lymphoproliferative responses for foals and adult horses. There was no significant difference in recall lymphoproliferative responses or IFN-gamma mRNA expression by bronchial lymph node lymphocytes between foals and adults. In contrast, interleukin 4 (IL-4) expression was significantly higher for adults than for foals for each of the Vap proteins. The ratio of IFN-gamma to IL-4 was significantly higher for foals than for adult horses for most Vap proteins. Therefore, foals are immunocompetent and are capable of mounting lymphoproliferative responses of the same magnitude and cytokine phenotype as those of adult horses.

Infecção pulmonar pelo Rhodococcus equi na síndrome da imunodeficiência adquirida: Aspectos na tomografia computadorizada

OBJETIVO: Apresentar os aspectos na tomografia computadorizada da pneumonia pelo Rhodococcus equi em sete pacientes com síndrome da imunodeficiência adquirida. MÉTODOS: Estudo retrospectivo das tomografias de sete pacientes com síndrome da imunodeficiência adquirida e infecção pelo Rhodococcus equi. RESULTADOS: Os achados mais freqüentes foram: consolidação (n = 7) com escavação (n = 6), opacidades em vidro fosco (n = 6), nódulos do espaço aéreo (n = 4) e nódulos centrolobulares com árvore em brotamento (n = 3). CONCLUSÃO: Os achados mais comuns na infecção pulmonar pelo Rhodococcus equi em pacientes com síndrome da imunodeficiência adquirida foram as consolidações escavadas.

Rhodococcus equi infection during treatment of a c-ANCA positive vasculitis: a case report

Rhodococcus equi is a rare form of opportunistic infection in humans, more common in the immunocompromised. We present a case of pulmonary infection and subsequent cerebral abscess secondary to R. equi in a patient receiving immunosuppression for a c-ANCA positive vasculitis. Heightened awareness of R. equi infection is important when considering immunocompromised patients presenting with sepsis, especially those with cavitating pulmonary lesions and normal respiratory commensals on culture. Delays in diagnosis and treatment can cause increased patient morbidity and mortality.

Hematologic and immunophenotypic factors associated with development of Rhodococcus equi pneumonia of foals at equine breeding farms with endemic infection

Rhodococcus equi causes severe pyogranulomatous pneumonia in foals and in immunocompromised people. In mice, both CD4+ and CD8+ T lymphocytes contribute to host defense against R. equi, but CD4+ T lymphocytes are required for pulmonary clearance of the bacteria. In this prospective study of 208 foals at two equine breeding farms with endemic R. equi infections, we collected peripheral blood samples at 2 and 4 weeks of age and at the time of diagnosis of R. equi pneumonia. Samples were analyzed for concentrations of total and differential leukocytes, EqCD4+ and EqCD8+ T lymphocytes, and B lymphocytes. Thirty (14.4%) foals developed R. equi pneumonia. At the 2nd week of life, affected foals had significantly lower concentrations of white blood cells (WBC) and segmented neutrophils, significantly lower proportions of EqCD4+ T lymphocytes, and significantly higher proportions of EqCD8+ T lymphocytes. The EqCD4:EqCD8 ratio was significantly lower for affected foals. At the 4th week of life, affected foals had significantly lower concentrations of segmented neutrophils and EqCD4+ T lymphocytes than did unaffected foals. The ratio of EqCD4:EqCD8 was significantly lower for affected foals. Two- and 4-week-old foals with ratios of EqCD4:EqCD8<3 were significantly more likely to develop R. equi pneumonia. There was a significant farm effect which diluted our statistical power to detect differences; however; after adjusting for the farm effect, 2-week-old foals with ratios of EqCD4:EqCD8<3 remained significantly more likely to develop R. equi pneumonia. There were no significant differences in immunophenotypic variables between affected foals (at the time of diagnosis) and age-matched control foals. These data suggest that there are hematologic and immunophenotypic differences between affected and unaffected foals during the first 2-4 weeks of life, prior to onset of clinical signs of R. equi pneumonia. These differences may represent important immunologic mechanisms associated with increased susceptibility of individual foals to infection with R. equi. Because there was considerable overlap between values for affected and unaffected foals, we cannot yet recommend immunophenotyping of foals at endemically-infected farms as a clinically useful screening tool to identify foals at increased risk of developing R. equi pneumonia.

Corynebacterium afermentans Lung Abscess and Empyema in a Patient with Human Immunodeficiency Virus Infection

Necrotizing pleuropulmonary infection in a patient with acquired immunodeficiency syndrome developed due to Corynebacterium afermentans subspecies lipophilum. Long-term combination antibiotic therapy was successful in eradicating the infection without surgery.

Prognosis and clinical evaluation of infection caused by Rhodococcus equi in HIV-infected patients: a multicenter study of 67 cases

OBJECTIVE

To assess the clinical characteristics and the factors that influenced the prognosis of patients with HIV and infection caused by Rhodococcus equi.

DESIGN

Observational, multicenter study in 29 Spanish general hospitals.

SETTING

These hospitals comprised a total of 20,250 beds for acute patients and served a population of 9,716,880 inhabitants.

PATIENTS

All patients with HIV and diagnosed R equi infection until September 1998.

RESULTS

During the study period, 19,374 cases of AIDS were diagnosed. Sixty-seven patients were included (55 male patients; mean +/- SD age, 31.7 +/- 5.8 years). At the time of diagnosis of R equi infection, the mean CD4+ lymphocyte count was 35/ micro L (range, 1 to 183/ micro L) and the stage of HIV infection was A3 in 10.4% of patients, B3 in 31.3%, C3 in 56.7%, and unknown in 1.5%. R equi was most commonly isolated in sputum (52.2%), blood cultures (50.7%), and samples from bronchoscopy (31.3%). Chest radiographic findings were abnormal in 65 patients (97%). Infiltrates were observed in all of them, with cavitations in 45 patients. The most active antibiotics against the strains isolated were vancomycin, amikacin, rifampicin, imipenem, ciprofloxacin, and erythromycin. After a mean follow-up of 10.7 +/- 12.8 months, 23 patients (34.3%) died due to causes related to R equi infection and 6 other patients showed evidence of progression of the infection. The absence of highly active antiretroviral therapy (HAART) was independently associated with mortality related to R equi infection (relative risk, 53.4; 95% confidence interval, 1.7 to 1,699). Survival of patients treated with HAART was much higher than that of patients who did not receive this therapy.

CONCLUSIONS

Infection by R equi is an infrequent, opportunistic complication of HIV infection and occurs during advanced stages of immunodepression. In these patients, it leads to a severe illness that usually causes a bacteremic, cavitary pneumonia, although HAART can improve the prognosis.

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.

In vitro susceptibilities of Rhodococcus equi and other common equine pathogens to azithromycin, clarithromycin, and 20 other antimicrobials

The objective of this study was to determine in vitro activities of azithromycin (AZM), clarithromycin (CLR), and 20 other antimicrobial agents against Rhodococcus equi and other common equine bacterial pathogens. A total of 201 bacterial isolates from various equine clinical samples were examined. CLR was more active than AZM against R. equi, with MICs at which 90% of the isolates were inhibited of 0.12 and 1.0 micro g/ml, respectively. Other antimicrobial agents highly active against at least 90% of R. equi isolates in vitro included rifampin, gentamicin, and imipenem. Both AZM and CLR showed good activity against beta-hemolytic streptococci and Staphylococcus spp. AZM was more active than other macrolides against Pasteurella spp. and Salmonella enterica.

Cerebral infection with Rhodococcus equi in a heart transplant recipient

Iatrogenic immunosuppression following organ transplantation leads to an increased number of opportunistic bacterial and viral infections. Similar to patients with human immunodeficiency virus (HIV) infection transplant recipients may suffer from rare infectious diseases. Herein we report on a patient presenting with a cerebral infection who had previously undergone orthotopic cardiac transplantation. Rhodococcus equi was isolated.

Rhodococcus equi: an emerging pathogen

More than 100 cases of Rhodococcus equi infection have been reported since the first description of human disease caused by this organism. The vast majority of patients infected with R. equi are immunocompromised, and two-thirds have human immunodeficiency virus infection. The clinical manifestations of R. equi infection are diverse, although 80% of patients have some pulmonary involvement. The organism is easily cultured from specimens of infected tissue or body fluid, but it may be misdiagnosed as a contaminant. Treatment is often prolonged, and relapses at distant sites are common. This article summarizes the history, diagnosis, clinical features, and treatment of infection with this emerging pathogen.

Rhodococcus equi pneumonia in a patient with human immunodeficiency virus: case report and review

Rhodococcus equi is a facultative, intracellular, gram-positive coccobacillus increasingly reported as an opportunistic pathogen in patients positive for human immunodeficiency virus (HIV). An HIV-positive man developed R. equi pneumonia and sepsis. He failed to improve despite surgical drainage of localized infection and many empiric antibiotics. Time-kill studies of R. equi isolated from the patient were performed against various antimicrobial agents to optimize therapy. Levofloxacin seemed to offer excellent in vitro bactericidal activity. Antagonism was observed with certain antibiotic combinations. Our anecdotal case report suggests that fluoroquinolones such as levofloxacin may offer superior efficacy to standard therapy in rhodococcal infections; their clinical utility deserves further investigation. In view of potential antagonism, prospective susceptibility testing for various drugs and drug combinations should be considered when clinically indicated.

Evaluation of E test, disk diffusion and broth microdilution to establish tentative quality control limits and review susceptibility breakpoints for two aerobic actinomycetes

A single laboratory study was carried out to compare E Test with broth microdilution and disk diffusion to establish tentative quality control ranges for Nocardia asteroides ATCC 19247 and Rhodococcus equi ATCC 6939 against a panel of eight antimicrobial agents. Reproducibility testing was performed on 12 consecutive days to establish tentative quality control ranges. A total of 36 clinical strains of the Nocardia asteroides complex and 5 Rhodococcus strains were used in the study. Both candidate control strains and clinical strains grew well on cation-adjusted Mueller-Hinton agar. Adequate growth occurred at 48 to 72 h for the Nocardia isolates and 24 to 48 h for Rhodococcus. A standardized primary inoculum of 5 x 10(4) CFU/mL was used for performance of E Test and disk diffusion for the Nocardia isolates. Tentative population-based error rates were calculated using current breakpoints for Enterobacteriaceae for E Test compared with disk diffusion for the 36 clinical strains of Nocardia species. Significant very major error rates were observed for imipenem (22%) and minor error rates varied from 2.7% to 50%. These methods require more extensive validation before definitive breakpoint criteria can be established.

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.

Modulation of cytokine response of pneumonic foals by virulent Rhodococcus equi

The ability of Rhodococcus equi to induce pneumonia in foals depends on the presence of an 85- to 90-kb plasmid. In this study, we evaluated whether plasmid-encoded products mediate virulence by modulating the cytokine response of foals. Foals infected intrabronchially with a virulence plasmid-containing strain of R. equi had similar gamma interferon (IFN-gamma) and interleukin-12 (IL-12) p35 but significantly higher IL-1beta, IL-10, IL-12 p40, and tumor necrosis factor alpha (TNF-alpha) mRNA expression in lung tissue compared to foals infected with the plasmid-cured derivative. IFN-gamma mRNA expression levels in CD4+ T lymphocytes isolated from bronchial lymph nodes (BLN) were similar for the two groups of R. equi-infected foals on day 3 postinfection. However, on day 14, in association with pneumonia and marked multiplication of virulent R. equi but with complete clearance of the plasmid-cured derivative, IFN-gamma mRNA expression in BLN CD4+ T lymphocytes was significantly (P < 0.001) higher in foals infected with the plasmid-cured derivative. These results suggests an immunomodulating role for R. equi virulence plasmid-encoded products in downregulating IFN-gamma mRNA expression by CD4+ T lymphocytes.

Role of the 85-kilobase plasmid and plasmid-encoded virulence-associated protein A in intracellular survival and virulence of Rhodococcus equi

Rhodococcus equi is a facultative intracellular pathogen of macrophages and a cause of pneumonia in young horses (foals) and immunocompromised people. Isolates of R. equi from pneumonic foals typically contain large, 85- or 90-kb plasmids encoding a highly immunogenic virulence-associated protein (VapA). The objective of this study was to determine the role of the 85-kb plasmid and VapA in the intracellular survival and virulence of R. equi. Clinical isolates containing the plasmid and expressing VapA efficiently replicated within mouse macrophages in vitro, while plasmid-cured derivatives of these organisms did not multiply intracellularly. An isolate harboring the large plasmid also replicated in the tissues of experimentally infected mice, whereas its plasmid-cured derivative was rapidly cleared. All foals experimentally infected with a plasmid-containing clinical isolate developed severe bronchopneumonia, whereas the foals infected with its plasmid-cured derivative remained asymptomatic and free of visible lung lesions. By day 14 postinfection, lung bacterial burdens had increased considerably in foals challenged with the plasmid-containing clinical isolate. In contrast, bacteria could no longer be cultured from the lungs of foals challenged with the isogenic plasmid-cured derivative. A recombinant, plasmid-cured derivative expressing wild-type levels of VapA failed to replicate in macrophages and remained avirulent for both mice and foals. These results show that the 85-kb plasmid of R. equi is essential for intracellular replication within macrophages and for development of disease in the native host, the foal. However, expression of VapA alone is not sufficient to restore the virulence phenotype.

Cytokine induction in murine macrophages infected with virulent and avirulent Rhodococcus equi

To look for a possible correlation between the virulence of Rhodococcus equi and its cytokine-inducing capacity, we evaluated intracellular survival and measured cytokine induction by mouse macrophages infected with a virulent strain containing an 85-kb plasmid and expressing VapA (103+), its avirulent plasmid-cured derivative (103-), and heat-killed 103+ (HK). After incubation with similar numbers of bacteria, macrophages infected with 103- contained significantly more organisms than those infected with 103+ or HK. The number of bacteria in the macrophages infected with 103- and HK decreased progressively, whereas the 103+ numbers remained constant over 48 h. Interleukin 1beta (IL-1beta), IL-6, IL-10, IL-12 p40, and tumor necrosis factor alpha (TNF-alpha) mRNA induction peaked at 4 h and returned to baseline between 12 and 48 h postinfection. IL-1beta, IL-6, IL-10, and TNF-alpha concentrations assessed by enzyme-linked immunosorbent assay generally agreed well with mRNA expression; IL-12 could, however, not be detected. For all the cytokines detected, mean concentrations in the supernatants were consistently higher in the 103(-)-infected monolayers than in those infected with 103+, although, with the exception of IL-1beta, the differences were not statistically significant. R. equi HK was a poor inducer of cytokine production. In conclusion, virulent and avirulent R. equi strains induced similar levels of cytokine synthesis. The slightly greater induction of most cytokines observed following infection with 103- is likely secondary to greater uptake by macrophages rather than to a direct role of VapA or another plasmid-encoded product in downregulating cytokine induction.