Ulcerative, granulomatous glossitis and enteritis caused by Rhodococcus equi in a heifer

Rhodococcus equi infection in horses is common and is characterized by pyogranulomatous pneumonia and ulcerative enterocolitis. R. equi clinical disease in cattle, however, is rare and typically manifests as granulomatous lymphadenitis discovered in the abattoir. A 19-mo-old female Santa Gertrudis had a history of intermittent inappetence and weight loss for a 3-mo period before euthanasia. Gross and histologic examination revealed severe, chronic, ulcerative, and granulomatous inflammation in the tongue, pharynx, and small intestine. Also, the heifer had severe, granulomatous pharyngeal and mesenteric lymphadenitis. Bacterial cultures from the ileum, tongue, and liver yielded numerous-to-moderate numbers of R. equi. PCR analysis of the isolate detected the linear virulence plasmid vapN, which is often identified in bovine isolates (traA- and vapN-positive). The bacteria also lack the circular plasmids vapA and vapB that are associated with virulence in horses and swine, respectively. We report herein an atypical and unusual clinical presentation of R. equi infection in cattle, which has zoonotic potential.

Identification of a VapA virulence factor functional homolog in Rhodococcus equi isolates housing the pVAPB plasmid

Rhodococcus equi is a facultative intracellular bacterium of macrophages and is an important pathogen of animals and immunocompromised people wherein disease results in abcessation of the lungs and other sites. Prior work has shown that the presence of the major virulence determinant, VapA, encoded on the pVAPA-type plasmid, disrupts normal phagosome development and is essential for bacterial replication within macrophages. pVAPA- type plasmids are typical of R. equi strains derived from foals while strains from pigs carry plasmids of the pVAPB-type, lacking vapA, and those from humans harbor various types of plasmids including pVAPA and pVAPB. Through the creation and analysis of a series of gene deletion mutants, we found that vapK1 or vapK2 is required for optimal intracellular replication of an R. equi isolate carrying a pVAPB plasmid type. Complementation analysis of a ΔvapA R. equi strain with vapK1 or vapK2 showed the VapK proteins of the pVAPB-type plasmid could restore replication capacity to the macrophage growth-attenuated ΔvapA strain. Additionally, in contrast to the intracellular growth capabilities displayed by an equine R. equi transconjugant strain carrying a pVAPB-type plasmid, a transconjugant strain carrying a pVAPB-type plasmid deleted of vapK1 and vapK2 proved incapable of replication in equine macrophages. Cumulatively, these data indicate that VapK1 and K2 are functionally equivalent to VapA.

Molecular analysis of the chromosomal 16S rRNA gene and vapA plasmid gene of Polish field strains of R. equi

Rhodococcus equi (R. hoagii) is an opportunistic pathogen commonly found in foals up to 6 months old and animal environment. The R. equi genome contains genetically stable chromosomal DNA and an 80–90 kb plasmid containing vapA gene, responsible for virulence. Most reports from around the world focus on the determination of R. equi plasmid profiles. Few studies have attempted to determine differences in nucleotide sequences between virulent strains of R. equi isolated from foals and breeding environment. The aim of the study was to perform a molecular analysis of a fragment of the chromosomal gene encoding the 16S rRNA subunit and the vapA plasmid gene of virulent R. equi strains isolated on Polish studs from foals and from the breeding environment of horses. The sequencing method was used to compare the primary structure of fragments of the chromosomal and plasmid DNA of the virulent R. equi strains. The sequences of 22 clinical and 18 environmental R. equi isolates were compared with the sequences of the gene fragments of reference strains available in the NCBI GenBank database. All sequenced 16S rRNA amplicons of Polish field strains were identical and showed 99.5% similarity to the four randomly selected sequences of this gene fragment in the GenBank database. The results confirm that fragments of the 16S rRNA gene of R. equi strains are highly conserved and do not undergo variation in field conditions. Analysis of the sequencing results for the vapA gene fragment of the strains used in our study revealed two polymorphic variants and clear differences between the sequences of strains isolated from foals and from soil samples. Presumably, R. equi strains present in the breeding environment are more exposed than clinical strains to adverse external factors. This may result in changes in the DNA sequence due to natural selection.

Purulent meningitis caused by Rhodococcus equi: A case report

RATIONALE

Purulent meningitis refers infection of the subarachnoid space by various purulent bacteria and the corresponding inflammation of the leptomeninges. However, purulent meningitis due to Rhodococcus equi is extremely rare.

PATIENT CONCERNS

A 40-year-old man presented with fever and intermittent headache for 6 days. Two hours prior to admission, he developed epileptic seizures.

DIAGNOSES

Brain computed tomography and magnetic resonance imaging showed intracerebral malacic lesions. Bacterial culture of cerebrospinal fluid revealed the presence of R. equi. A diagnosis of purulent meningitis caused by R. equi was made.

INTERVENTIONS

The patient was treated with intravenous meropenem (1000 mg every 8 hours) for 19 days; then he was discharged and instructed to continue the intravenous meropenem for two weeks. After a follow-up period of 2 months, the patient had recovered completely.

OUTCOMES

After a follow-up period of 2 months, the patient had recovered completely.

LESSONS

Central nervous system infection caused by R. equi is rare. Early bacterial culture of CSF is important for timely diagnosis. With sufficient antibiotic therapy, the prognosis can be favorable.

Isolated Mediastinal Lymphadenopathy Caused by Rhodococcus equi Infection

Mediastinal lymphadenopathy is common finding in thoracic surgery, and it often requires morphologic confirmation to establish the definitive diagnosis. The most frequent diagnoses are metastatic lung cancer, sarcoidosis, lymphoma, tuberculosis, and other causes of granulomatous infections. Rhodococcus equi is a rare pathogen in humans that mostly affects immunocompromised patients. This report presents a case with isolated mediastinal lymphadenopathy caused by Rhodococcus equi infection in a 71-year-old immunocompetent patient.

Detection of vapN in Rhodococcus equi isolates cultured from humans

Rhodococcus equi can cause severe infections in people, particularly in immunocompromised individuals. The R. equi virulence plasmids (vap) encoding vapA and vapB are linked to development of infections in domestic animals. Recently, a novel virulence plasmid, vapN, was identified in isolates cultured from cattle, but its prevalence or significance in human R. equi infections has not been extensively studied. To determine the prevalence of vapN in a diverse collection of human-derived isolates from different countries, 65 R. equi isolates collected by various institutions from 1984 to 2002 were screened for the presence of vapN and other virulence plasmids through polymerase chain reaction (PCR) using redesigned primer sets. Of the isolates that carried plasmids, 43% (16/37) were vapN-positive and fewer were vapB or vapA-positive (30 and 16%, respectively). This is the first report of vapN carriage in R. equi isolated from human infections. One isolate (H-30) carried vapN but did not amplify the conjugal plasmid transfer gene traA associated with carriage of vap, which could be explained by sequence variation within the traA gene. Another isolate (H-55) amplified traA, but did not amplify vapA, B, or N (traA⁺vapABN^-) with previously described primer sets or those developed for this study. The H-55 traA sequence had 98% identity to traA sequences in vapA plasmids, which suggests that it may carry a variant of previously characterized virulence plasmids or a novel virulence plasmid. Carriage of vapN in R. equi isolates derived from people is not uncommon and more research is needed to determine its significance in the epidemiology and pathogenesis of human R. equi infections.

Two Cases of Equine Abortion Caused by Rhodococcus equi

Rhodococcus equi was isolated from lung, liver, spleen, and stomach content of two aborted equine fetuses of 7 and 8 months gestation from two different farms. Lesions included diffuse pyogranulomatous pneumonia with numerous Gram-positive coccobacilli within the cytoplasm of macrophages, multinucleated Langhans giant cells and neutrophils, and enhanced extramedullary hematopoiesis with megakaryocytosis within the liver and spleen. Detection of R. equi was made by bacteriology and immunohistochemistry for R. equi and VapA, the virulence factor of R. equi. R. equi and VapA were identified within the lungs of both fetuses, and its distribution correlated with lesions. Fetal lesions were similar to those observed in foals. We speculate that the fetuses contracted infection from the placenta by normal breathing movements or by swallowing of the amniotic fluid contaminated with R. equi.

Plasmid Profiles of Virulent Rhodococcus equi Strains Isolated from Infected Foals in Poland

Rhodococcus equi is an important bacterial pathogen in foals up to 6 months old, widespread in horse farms all over the world. It was found that only virulent R. equi strains expressing 15–17 kDa virulence-associated protein (VapA) and having large virulence plasmid of 85–90 kb containing vapA gene are pathogenic for horses. To date, 12 plasmid types have been reported in VapA positive strains from horses. There are no data concerning plasmid types of Polish field R. equi strains isolated from horses and horse farm environment. The aim of the study is to determine plasmid profiles of virulent R. equi strains isolated in Poland from dead foals as well as from soil samples taken from horse breeding farms. Plasmid profiles of 10 clinical strains derived from 8 farms and 11 environmental strains from 3 farms, confirmed as virulent by PCR, were compared with 12 reference strains containing the known plasmid size and type. Plasmid DNAs were analysed by digestion with the restriction endonucleases BamHI, EcoRI, EcoT22I, and HindIII for detailed comparison and estimation of plasmid sizes. The results of RFLP analysis revealed that all except one isolates used in the study are classified as VapA 85 kb type I plasmid. One strain harboured VapA 87 kb type I plasmid. This is the first report of plasmid types of Polish field R. equi strains. The results of our preliminary investigations on horse farms located in central and eastern Poland indicate that the virulent R. equi strains thus far isolated from diseased foals and horse farms environment represent a highly uniform plasmid pattern.

Mutant prevention concentration and mutant selection window for 10 antimicrobial agents against Rhodococcus equi

The objectives of this study were to determine the mutant prevention concentration (MPC), time above the MPC and mutant selection window for 10 antimicrobial agents against Rhodococcus equi and to determine if the combination of a macrolide with rifampin would decrease emergence of resistant mutants. Antimicrobial agents investigated (erythromycin, clarithromycin, azithromycin, rifampin, amikacin, gentamicin, enrofloxacin, vancomycin, imipenem, and doxycycline) were selected based on in vitro activity and frequency of use in foals or people infected with R. equi. Each antimicrobial agent or combination of agents was evaluated against four virulent strains of R. equi. MPC were determined using an agar plate assay. Pharmacodynamic parameters were calculated using published plasma and pulmonary pharmacokinetic variables. There was a significant (P<0.001) effect of the type of antimicrobial agent on the MPC. The MPC of clarithromycin (1.0 μg/ml) was significantly lower and the MPC of rifampin and amikacin (512 and 384 μg/ml, respectively) were significantly higher than that of all other antimicrobial agents tested. Combining erythromycin, clarithromycin, or azithromycin with rifampin resulted in a significant (P≤0.005) decrease in MPC and MPC/MIC ratio. When MIC and MPC were combined with pharmacokinetic variables, only gentamicin and vancomycin were predicted to achieve plasma concentrations above the MPC for any given periods of time. Only clarithromycin and the combination clarithromycin-rifampin were predicted to achieve concentrations in bronchoalveolar cells and pulmonary epithelial lining fluid above the MPC for the entire dosing interval. In conclusion, the combination of a macrolide with rifampin considerably decreases the emergence of resistant mutants of R. equi.

Rhodococcus equi granulomatous mastitis in an immunocompetent patient

A 37-year-old immunocompetent woman was evaluated for progressive swelling of her left breast. Magnetic resonance imaging (MRI) showed multiple hypo-intense solid lesions and could not exclude breast cancer. Tissue biopsy was suggestive of granulomatous mastitis without any evidence of malignancy. Culture of the specimen in brain heart infusion broth grew Rhodococcus equi. The patient responded well to combination therapy with ciprofloxacin and azithromycin, and the lesions regressed in follow-up MRI. To the best of our knowledge, this is the first report of R. equi granulomatous mastitis. Accurate identification of this rare pathogen is necessary to provide appropriate treatment in granulomatous mastitis.

Streptolysin-O/antibiotics adjunct therapy modulates site-specific expression of extracellular matrix and inflammatory genes in lungs of Rhodococcus equi infected foals

The addition of streptolysin-O (SLO) to the standard antibiotics regimen was shown to be superior to antibiotics alone after experimental infection of foals with Rhodoccocus equi (R. equi). The objective of this study is to investigate this response by determining the site-specific expression of extracellular matrix (ECM) and inflammatory response genes in biopsy samples taken from three distinct lung regions of the infected foals. Twenty-four foals were challenged by intrabronchial instillation of R. equi and assigned to four treatment groups: SLO/antibiotics adjunct therapy, antibiotics-only therapy (7.5 mg/kg clarithromycin and 5 mg/kg rifampin), SLO-only, and saline-only treatments. Treatments were administered twice daily for 16 days unless symptoms progressed to the point where the foals needed to be euthanized. Gene expressions were determined using custom-designed equine real-time qPCR arrays containing forty-eight genes from ECM remodeling and inflammation pathways. A non-parametric Wilcoxon signed-rank test for independent samples was applied to two pairs of time-matched comparison groups, SLO/antibiotics vs. antibiotics-only and SLO-only vs. saline-only, to document the significant differences in gene expressions within these groups. Several genes, MMP9, MMP2, TIMP2, COL1A1, COL12A1, ITGAL, ITGB1, FN1, CCL2, CCL3, CXCL9, TNFα, SMAD7, CD40, IL10, TGFB1, and TLR2, were significantly regulated compared to the unchallenged/untreated control foals. The results of this study demonstrate that enhancement of clinical responses by SLO is consistent with the changes in expression of critical genes in ECM remodeling and inflammatory response pathways.

[First molecular detection of Rhodococcus equi in a HIV/AIDS patient in Cuba]

INTRODUCTION

Rhodococcus equi is recognized as an emerging pathogen that causes important morbidity and mortality among immunocompromised patients.

OBJECTIVE

to confirm the presence of R. equi in pleural fluid through the restriction fragment length polymorphism technique.

METHODS

the pleural fluid sample from one AIDS patient with respiratory symptoms was used. Microbiologic culture, staining tests, phenotypic and biochemical tests and restriction fragment length polymorphism technique for the diagnosis of microorganism were performed.

RESULTS

the staining technique along with the phenotypic and biochemical tests provided the presumptive diagnosis of R. equi infection, which was further confirmed by the molecular techniques.

CONCLUSIONS

this paper reported the molecular detection of R. equi from one HIV/aids patient for the first time in Cuba. The results suggested that the molecular biology techniques could be used in the diagnosis and identification of R. equi.

Hemodialysis catheter related rhodococcus bacteremia in immunocompetent host

Rhodococcus equi (R. equi) is an uncommon cause of infection in immunocompetent individuals. We describe a case of R. equi bacteremia associated with hemodialysis (HD) catheter in an immunocompetent patient. A 38-year-old female with end-stage renal disease (ESRD) of uncertain etiology, on HD for the past 15 months who was previously healthy otherwise, was admitted with the complaints of intermittent fever, mild nausea and occasional vomiting for two weeks. Last HD was performed four days earlier through a tunneled right internal jugular permacath. Clinically the patient was afebrile and in no acute distress. She was hemodynamically stable with no peripheral stigmata of an endovascular infection. Physical examination was essentially normal. Initially, the patient was treated with intravenous vancomycin with each HD, retaining the catheter. However, due to persistently positive blood cultures, HD catheter had to be removed. The patient became afebrile and nausea and vomiting resolved. She improved clinically, and repeated surveillance blood cultures done after the removal of catheter were reported negative. Subsequently, a new HD catheter was inserted for her. Although R. equi is an uncommon cause of infection in immunocompetent individuals, it does occur with considerable mortality and morbidity, and a high index of clinical suspicion is required to recognize this infection in immunocompetent individuals.

Invasive infection with Rhodococcus equi--two case reports and review of literature

Rhodococcus equi infection is rare in humans, but has increasingly been reported in the last three decades, particularly in immunocompromised patients. The infection is mainly pulmonary but can also assume an extra-pulmonary form. R. equi infection is difficult to diagnose at an early stage both from a clinical and microbiologic view. Only correct and timely diagnosis and treatment can help reduce significant morbidity and mortality. Optimal treatment probably consists of prolonged, preferably triple combination therapy, including vancomycin, with optimization of pharmacokinetic parameters and screening for drug interactions, when indicated. Two clinical cases of invasive R. equi infection are reported in this manuscript: a pulmonary form and an extra-pulmonary form with brain abscesses, both in immunocompromised patients, with detailed description of symptoms, analysis, treatment, and outcome.

Comparison of concentrations of Rhodococcus equiand virulent R. equi in air of stables and paddocks on horse breeding farms in a temperate climate

REASONS FOR PERFORMING STUDY

Rhodococcoccus equi is a significant cause of bronchopneumonia in foals worldwide. Infection of the lungs is believed to result from inhalation of virulent R. equi in dust from contaminated environments. A measure of infectious risk in an environment is the level of airborne contamination.

OBJECTIVES

To assess and compare the level of airborne virulent R. equi in paddocks and stables.

METHODS

Air samples were collected sequentially over the 2003 foaling season from the paddocks and stables on 3 Irish horse breeding farms affected by R. equi pneumonia. Colony blotting and DNA hybridisation techniques allowed quantitation of virulent R. equi.

RESULTS

The odds of detecting airborne virulent R. equi in stables were 173 times greater than in paddocks. The median airborne concentration of virulent R. equi was significantly higher (P < 0.001) in stables than in paddocks on all farms. These observations suggested that stables were high-risk areas for infection.

CONCLUSIONS AND POTENTIAL RELEVANCE

Our results indicate that contaminated stables are a significant risk factor in the epidemiology of R. equi pneumonia on horse-breeding farms in a temperate climate, such as in Ireland. Management strategies that improve the air hygiene of stables, through better ventilation, use of less fragile bedding material and the use of fogging agents to reduce the airborne concentration of virulent R. equi, may reduce the incidence and severity of R. equi pneumonia on farms.

The suitability of selected methods of nucleic acid extraction for detecting Rhodococcus equi DNA in tracheobronchial wash fluid using PCR

The aim of the present study was to compare the effectiveness of selected DNA extraction methods for the detection of Rhodococcus equi from tracheobronchial wash fluid by PCR. Three methods of nucleic acid extraction were evaluated, based mainly on the activity of proteolytic enzymes. A commercial kit for isolation and purification of bacterial DNA was also used in the study. In one procedure, an additional component, the cationic detergent CTAB, was used. It has been found that the traditional enzyme digestion methods used with the tracheobronchial wash fluid are more suitable to prepare DNA matrix for PCR comparing with commercial DNA isolation kit. Minimum numbers of bacteria detected with the use of traditional enzyme digestion methods and commercial kit were 100 and 500 cells, respectively. Based on the results of the study we can recommend the enzymatic digestion method along with CTAB as an additional component.

Immunohistological demonstration of Rhodococcus equi in a trotter foal

A 3-month-old female trotter foal was euthanized due to severe dyspnoea. Pathomorphologically a chronic granulomatous to necrotizing pneumonia was found and Rhodoccocus (R.) equi was isolated microbiologically. An immunohistological method using a murine monoclonal antibody against a 15-17 kDa antigen of virulent R. equi was established in formalin-fixed and paraffin-embedded tissue sections using various antigen retrieval techniques to optimize the staining results. Microwave treatment was most suitable for the demonstration of bacterial antigen localized predominantly in intralesional macrophages. Immunohistology is an additional method for identifying R. equi-infections in equine tissue and may be useful in retrospective studies on paraffin-embedded archive material.

Rhodococcus equi infection in a surgical wound

A 35-year-old male presented with abdominal pain one month after receiving a routine ventral hernia repair. Over the course of two months, repeated wound cultures were ordered and eventually produced growth of Rhodococcus equi. Appropriate antibacterial therapy was initiated to resolve the infection.

Rhodococcus lung abscess complicating kidney transplantation: successful management by combination antibiotic therapy

In this report, a renal transplant recipient with Rhodococcus lung abscess is described. A high clinical suspicion and appropriate combination antibiotic therapy obviated the need for surgical intervention and was associated with a good clinical outcome. The optimal regimen of combination antibiotic therapy is discussed.

Abortion in a thoroughbred mare associated with an infection with avirulent Rhodococcus equi

An eight-year-old thoroughbred mare with no previous history of illness aborted a fetus at 196 days of gestation, and its internal tissues were examined immunohistologically and bacteriologically. The placenta was not examined, but specimens of the intrauterine fluids and the dam's faeces were collected four days after the abortion and examined bacteriologically. No significant histological lesions were found in the fetus but the amnion and the umbilical cord were oedematous and had petechial haemorrhages. Rhodococcus equi was isolated in pure culture from the lung, heart and stomach contents of the fetus and from an intrauterine specimen and faeces of the dam. The anti-R equi antibody titre of the mare was high after the abortion. The diagnosis was confirmed in the lung of the fetus by immunohistochemical staining with R equi-specific antibodies. Isolates from the fetus and mare were identified as avirulent R equi by pcr and the mouse pathogenicity test. The avirulent isolates were characterised by pulsed-field gel electrophoresis, which yielded only one VspI profile in all the isolates from the fetus and its dam.

Rhodococcus equi lung infection in an allogeneic hematopoietic stem cell transplant recipient

In this report, we describe a case of Rhodococcus equi lung infection diagnosed in an allogeneic hematopoietic stem cell transplant with oral graft-versus-host disease 3 months after stem cell infusion. The lung lesion persisted despite an approximate 3 months of vancomycin therapy, but then responded favorably to a combination of intravenous ertapenem at 1 g daily and oral rifampin at 600 mg daily for 1 month. An overview of Rhodococcus infection in transplant recipients is presented. This case and the discussed literature suggest that combination antibiotic therapy is warranted in patients with decreased humoral and cellular immunity.

Recurrent Rhodococcus equi infection with fatal outcome in an immunocompetent patient

The majority of human Rhodococcus equi infections occur in immunocompromised hosts, especially those with AIDS, and infection in immunocompetent patients is rare. Reported here is a case of R. equi infection in a seemingly healthy patient with a very complicated course. Despite neurosurgery and prolonged antibiotic therapy the patient deceased.

[Detection of rhodococcus equi by microbiological culture and by polymerase chain reaction in samples of tracheobronchial secretions of foals]

The goal of the present study was to investigate whether new PCR-methods would improve diagnostic of R. equi. In a first step, sensitivity and specificity of the PCR-methods in respect to the"gold standard" microbiological culture were determined. Secondly, sensitivity and specificity of both microbiological methods were evaluated in respect to the clinical diagnosis. The tracheobronchial secretions of 48 foals with pulmonary abscesses and of 37 healthy foals were evaluated by bacteriological culture as well as by four PCR-methods: aceA-, ideR-, vapA- and VP-PCR. In respect to the"gold standard" microbiological culture, the sensitivity of most PCR methods lay between 63.9 and 69.4 % except the vapA-PCR (27.8 %). The specificity of all PCR methods in this comparison was between 98 to 100 %. In this analysis, clinical diagnosis had a low sensitivity (66.7 %) and a low specificity (51.0 %). In respect to the clinical diagnosis, microbiological culture sensitivity was 50.0 % and specificity 67.7 9%. In this analysis, sensitivity rates of aceA-, ideR and VP-PCR methods lay between 33.3 and 37.5 %, sensitivity of the vapA-PCR was lower (10.4 %). The specificity of all PCR methods ranged from 78.4 to 86.5 %. In conclusion, these results show that the diagnostic potential of the microbiological methods"Culture" and "PCR" is different and that for the diagnosis of R. equi-pneumonia in foals the combination of microbiological culture with PCR should be used for examination of samples of the airways of foals.

Oral administration of a live attenuated Salmonella vaccine strain expressing the VapA protein induces protection against infection by Rhodococcus equi

Rhodococcus equi remains one of the most important pathogens of foals and vaccination strategies to prevent rhodococcosis are under increasing investigation. Attenuated Salmonella strains carrying heterologous antigens offer an advantageous alternative to conventional vaccines, especially because they induce mucosal and systemic immunity. In this work, we expressed the VapA antigen from R. equi in a Salmonella enterica Typhimurium strain, which was able to colonize and persist in the lymphoid tissue of BALB/c mice. Two days after being challenged, oral immunized mice presented a 3- to 7-fold increase in R. equi clearance. This was progressively enhanced during infection and, on the 10th day, a CFU value 50-fold lower than that recovered from non-immunized mice was attained. The number of hepatic granulomas was 2 times lower, and leukocyte infiltration was transiently detected in immunized mice, contrasting with the severe inflammation and necrosis presented by non-immunized mice. Infection with 1 x 10(7)R. equi CFU caused 100% mortality in the control groups, while all immunized mice survived. This protection was associated with the detection of high levels of anti-VapA IgG in the serum of the vaccinated mice, predominantly the IgG2a isotype. Our results suggest that attenuated Salmonella encoding VapA may be used in foals to prevent rhodococcosis.

Comparison of two selective media for the recovery, isolation, enumeration and differentiation of Rhodococcus equi

The use of selective media to facilitate the isolation of Rhodococcus equi from environmental and clinical samples has aided studies of the ecology of R. equi and the epidemiology of disease caused by R. equi. Here, we compared the efficacy of two selective media (NANAT and modified CAZ-NB) for the recovery of six defined strains of R. equi and for the isolation and enumeration of both avirulent and virulent R. equi from 60 paired soil samples from horse farms using colony blotting and DNA hybridisation. No difference was found between the two media in the recoverability of defined strains of R. equi or the proportion of soil cultures positive for R. equi or virulent R. equi. NANAT medium was significantly less inhibitory of bacterial growth from soil culture compared to mCAZ-NB (P = 0.001), but there was no difference between the media in the number of R. equi colonies recovered. Soil cultured on mCAZ-NB medium yielded a significantly greater number of virulent R. equi colonies than NANAT (P = 0.03). The proportion of R. equi that were virulent in soil cultures on mCAZ-NB (32%) was more than three times that seen in cultures on NANAT (9%). Thus modified CAZ-NB appeared to be a better selective media for studies where the optimal recovery of virulent R. equi is required, such as in studies of the gastrointestinal carriage of virulent R. equi and of subclinically infected foals.

[Pulmonary malakoplakia and Rhodococcus equi infection. A report of two cases and review]

Malakoplakia is a rare, chronic, granulomatous disease seen in immunocompromised patients, caused by multiple infectious agents, most often bacteria. Microscopically, accumulations of macrophages with granular cytoplasm and intra- or extracellular structures, called Michaelis-Gutmann bodies are characteristic. Main cause of pulmonary malakoplakia is Rhodococcus equi infection. We report two cases of pulmonary malakoplakia, in one case R. equi infection was confirmed. We also present a summary of recent knowledge about the pathogenesis, morphology and clinical course of the disease.

Cerebellar abscess due to Rhodococcus equi in an immunocompetent patient: case report and literature review

Rhodococcus equi (R. equi) is a facultative, intracellular, nonmotile, non-spore-forming, gram-positive coccobacillus, primarily causes zoonotic infections that affect grazing animals, mainly horses and foals and is a rare opportunistic pathogen found in severely compromised patients, and most commonly in recent years, in human immunodeficiency virus (HIV)-infected persons. Early cases, most in patients receiving immunosuppressant therapy, were more likely to be successfully treated with antimicrobial agents than cases in AIDS patients, it is emerging as an important pathogen in patients with cellular immune deficiency. We report a case of an immunocompetent 37 year-old patient with cerebellar abscess location that seems to be the only thin to today described in the literature. R. equi is a facultative, intracellular, nonmotile, non-spore-forming, gram-positive coccobacillus, primarily causes zoonotic infections that affect grazing animals, mainly horses and foals and is a rare opportunistic pathogen found in severely compromised patients, and most commonly in recent years, in human immunodeficiency virus (HIV)-infected persons. Early cases, most in patients receiving immunosuppressant therapy, were more likely to be successfully treated with antimicrobial agents than cases in AIDS patients, it is emerging as an important pathogen in patients with cellular immune deficiency. We report a case of an immunocompetent 37 year-old patient with cerebellar abscess location that seems to be the only thin to today described in the literature.

Bacteremia por Rhodococcus equi em paciente com síndrome da imunodeficiência adquirida: relato de caso

Rhodococcus equi é um importante agente de infecções zoonóticas, podendo causar sérias infecções em humanos, principalmente em pacientes imunocomprometidos. Neste estudo, nós relatamos o caso de uma bacteremia fatal devido a Rhodococcus equi em paciente com síndrome da imunodeficiência adquirida (HIV positivo).

Granulomatous lesions in lymph nodes of slaughter pigs bacteriologically negative for Mycobacterium avium subsp. avium and positive for Rhodococcus equi

The prevalence of granulomatous lesions in lymph nodes of pigs was studied. From January till August 2004 in two slaughterhouses in The Netherlands 2,116,536 pigs were examined for the presence of granulomatous lesions in the sub-maxillary lymph nodes. In 15,900 (0.75%) of these pigs, lesions could be detected. Nine farms with the highest incidence of lesions were selected for a more detailed pathological and bacteriological examination. On these farms, the prevalence of lesions in sub-maxillary lymph nodes ranged from 2.3 to 5.7% with a mean of 3.0%. From 1276 pigs that were sampled, 98 (7.7%) displayed granulomatous lesions in the sub-maxillary lymph nodes and one (0.1%) pig showed lesions in its mesenteric lymph node. Mycobacterium avium subsp. avium (MAA) could not be isolated from the lymph nodes of the 99 pigs with lesions and from a selection of lymph nodes (n=61) of pigs without lesions. Rhodococcus equi was isolated from 44 out of 98 (44.9%) of the sub-maxillary lymph nodes with granulomatous lesions and from two mesenteric lymph nodes without lesions. A comparison of former studies and the current results indicate that the prevalence of MAA infections in slaughter pigs has strongly decreased over the last decade, whereas R. equi is highly prevalent. The high incidence of granulomatous lesions associated with the bacteriological presence of R. equi could be considered as a serious cause of misdiagnosis of MAA infections in cases where meat inspection is carried out by inspection for granulomatous changes of lymph nodes only.

Associations between the ecology of virulent Rhodococcus equi and the epidemiology of R. equi pneumonia on Australian thoroughbred farms

The ecology of virulent strains of Rhodococcus equi on horse farms is likely to influence the prevalence and severity of R. equi pneumonia in foals. This study examined the association between the ecology of virulent R. equi and the epidemiology of R. equi pneumonia by collecting air and soil samples over two breeding seasons (28 farm-year combinations) on Thoroughbred breeding farms with different reported prevalences of R. equi pneumonia. Colony blotting and DNA hybridization were used to detect and measure concentrations of virulent R. equi. The prevalence of R. equi pneumonia was associated with the airborne burden of virulent R. equi (both the concentration and the proportion of R. equi bacteria that were virulent) but was not associated with the burden of virulent R. equi in the soil. Univariable screening and multivariable model building were used to evaluate the effect of environmental and management factors on virulent R. equi burdens. Lower soil moisture concentrations and lower pasture heights were significantly associated with elevated airborne concentrations of virulent R. equi, as were the holding pens and lanes, which typically were sandy, dry, and devoid of pasture cover. Few variables appeared to influence concentrations of virulent R. equi in soil. Acidic soil conditions may have contributed to an elevated proportion of virulent strains within the R. equi population. Environmental management strategies that aim to reduce the level of exposure of susceptible foals to airborne virulent R. equi are most likely to reduce the impact of R. equi pneumonia on endemically affected farms.

Rhodococcus equi in the soil environment of horses in Inner Mongolia, China

Little is known about the distribution of Rhodococcus equi in the soil environment of native horses in China. One hundred and eight soil samples were collected from native-horse farms in the Hulun Beier grasslands of eastern Mongolia, the Xilin Goler grasslands of southern Mongolia, and Tongliao City in Inner Mongolia, China. The isolation rates of R. equi from soil samples from the Hulun Beier and Xilin Goler grasslands ranged from 25.9% to 30.0%. In contrast, isolation rates from soil samples from Tongliao City were as high as 82.3% and the mean number of R. equi in soil samples from Tongliao City was 10 times more than those of samples from the grasslands. The 488 isolates were examined using PCR for the presence of genes that encode virulence-associated 15-17 kDa antigen protein (VapA) and the 20 kDa antigen protein (VapB). All isolates were negative for virulence-associated proteins. Plasmid profiles of these avirulent isolates showed that cryptic plasmids of various sizes were present with an incidence of 13.3% to 21.5%. The results of the present study contrast with those of our recent study (J. Vet. Med. Sci. 67:611-613, 2005), in which we reported that R. equi was absent from Mongolian horses in Ulaanbaatar, Mongolia. It is suggested that the difference between the results of these two studies is due to the mobile pasturing system in Mongolia and nonmobile pasturing system in Inner Mongolia.

Intracellular success: cytologic findings in an ulcerated submandibular mass from a cat

A 1-year-old neutered male domestic shorthair cat had an ulcerated, proliferative lesion in the submandibular area that did not respond to antibiotic therapy. Impression smears from the mass revealed septic pyogranulomatous inflammation, with large numbers of pleomorphic bacteria observed intracellularly within macrophages as well as neutrophils. Bacterial culture was consistent with a diagnosis of Rhodococcus equi, a facultative intracellular coccobacillus capable of replicating within macrophages. The cat's lesion resolved after treatment with rifampin and clarithromycin. R equi should be considered as a differential diagnosis when coccobacilli are recognized within macrophages in cytologic samples.

Seroepidemiological survey of Rhodoccocus equi infection in asymptomatic horses from Bursa, Izmir and Istanbul provinces, Turkey

In order to assess the Rhodococcus equi infection in three provinces of Turkey (Bursa, Izmir and Istanbul), 696 sera from healthy foals and adult horses were tested by indirect ELISA using a R. equi reference strain (ATCC 6939) as antigen. 103 sera (14.80%) with titres >0.646 resulted positive. Seroprevalence was significantly higher (P=0.0053) in male than in female horses of Istanbul province, although higher antibody titres (mean value) were observed in the female group of Bursa and Izmir provinces with differences estimated between provinces (P=0.0002). Seroprevalence was correlated with age: foals aged less than 1 year (P<10(-4)) and horses from 5 to 10 years old (P=0.018) resulted more infected in Bursa and Izmir provinces. Our findings indicate that R. equi infection actually occurs in all investigated provinces, suggesting the importance of serological survey to diagnose the infection and to prevent the zoonotic risk.

Internally controlled real-time PCR method for quantitative species-specific detection and vapA genotyping of Rhodococcus equi

We developed a novel quantitative real-time PCR (Q-PCR) method for the soil actinomycete Rhodococcus equi, an important horse pathogen and emerging human pathogen. Species-specific quantification was achieved by targeting the chromosomal monocopy gene choE, universally conserved in R. equi. The choE Q-PCR included an internal amplification control (IAC) for identification of false negatives. A second Q-PCR targeted the virulence plasmid gene vapA, carried by most horse isolates but infrequently found in isolates from other sources. The choE-IAC and vapA assays were 100% sensitive and specific as determined using 178 R. equi isolates, 77 nontarget bacteria, and a panel of 60 R. equi isolates with known vapA+ and vapA-negative (including vapB+) plasmid genotypes. The vapA+ frequency among isolate types was as follows: horse, 85%; human, 20%; bovine and pig, 0%; others, 27%. The choE-IAC Q-PCR could detect up to one genome equivalent using R. equi DNA or 100 bacteria/ml using DNA extracted from artificially contaminated horse bronchoalveolar lavage (BAL) fluid. Quantification was linear over a 6-log dynamic range down to approximately 10 target molecules (or 1,000 CFU/ml BAL fluid) with PCR efficiency E of >0.94. The vapA assay had similar performance but appeared unsuitable for accurate (vapA+) R. equi quantification due to variability in target gene or plasmid copy number (1 to 9). The dual-reaction Q-PCR system here reported offers a useful tool to both medical and veterinary diagnostic laboratories for the quantitative detection of R. equi and (optional) vapA+ "horse-pathogenic" genotype determination.

Clinical evaluation of a peptide-ELISA based upon N-terminal B-cell epitope of the VapA protein for diagnosis of Rhodococcus equi pneumonia in foals

A total of 227 field samples from naturally exposed foals aged between 3 weeks and 6 months were used in an evaluation of a peptide-based enzyme-linked immunosorbent assay (ELISA) for diagnosis of Rhodococcus equi infection. A biotinylated peptide derived from the virulence-associated protein A (VapA) of R. equi, a horse pathogen, was synthesized and designated as PN11-14. The peptide corresponds to the N-terminal B-cell epitope TSLNLQKDEPNGRASDTAGQ of the VapA protein. Based upon a serum immunoglobulin (Ig)G titre of 512 as a positive cut-off value for the R. equi infection, the ELISA provided the overall sensitivity of 47.62%, specificity of 69.67% and an accuracy of 59.47% with a positive predictive value of 57.47% for true R. equi pneumonia. The assay was improved by detecting VapA-specific IgGb antibodies against N-terminal B-cell epitope of the VapA protein rather than IgG antibodies. The VapA-IgGb ELISA showed the overall sensitivity of 70.47%, specificity of 72.13% and accuracy of 71.36% with a positive predictive value of 68.52%. Diagnosis of R. equi disease in 6-week-old foals showed that the VapA-IgGb ELISA provided an increasing trend (P=0.0572) in sensitivity of 82.4% in comparison with the VapA-IgG ELISA which showed the sensitivity of 58.8%. However, differences in specificity of both tests were statistically insignificant (P=0.357) as analysed by the McNemar test. These results indicated that detection of VapA-specific IgGb antibodies may be a better predictor of R. equi disease in foals.

Plasmid profiles of virulent Rhodococcus equi isolates from soil environment on horse-breeding farms in Hungary

The plasmid profiles of virulent Rhodococcus equi strains isolated on three horse-breeding farms located in different parts of Hungary were investigated. From 49 soil samples collected on the three farms, 490 R. equi isolates (10 from each sample) were obtained and tested for the presence of 15- to 17-kDa antigens (VapA) by immunoblotting and PCR. Ninety-eight VapA-positive isolates were detected from 30 of the 49 culture-positive samples with a prevalence ranging from 13.1% to 23.2%. Of the 98 virulent isolates, 70 contained an 85-kb type I plasmid, 13 contained an 87-kb type I plasmid, and 15 contained an 85-kb type III plasmid which had been uniquely isolated from soil isolates in the United States. This study demonstrates that the virulent form of R. equi is very widespread in the soil environment of these stud farms in Hungary and the plasmid pattern is different from farm to farm.

Intracranial abscess caused byRhodococcus equiinfection in a foal

CASE DESCRIPTION

A 4-month-old Missouri Fox Trotter colt was examined for a 5-week history of head tilt after treatment for suspected pulmonary Rhodococcus equi infection.

CLINICAL FINDINGS

Computed tomography revealed osteolysis of the occipital, temporal, and caudal portion of the parietal bones of the left side of the cranium. A soft tissue mass compressing the occipital region of the cerebral cortex and cerebellum was associated with the osteolytic bone.

TREATMENT AND OUTCOME

A rostrotentorial-suboccipital craniectomy approach was performed to remove fragmented occipital bone, debulk the intracranial mass, and obtain tissue samples for histologic examination and bacterial culture. All neurologic deficits improved substantially within 3 days after surgery. Bacterial culture of the resected soft tissue and bone fragments yielded R equi.

CLINICAL RELEVANCE

Intracranial surgery in veterinary medicine has been limited to dogs and cats; however, in select cases, extrapolation of surgical techniques used in humans and small animals can assist with intracranial procedures in horses.

Protective role of neutrophils in mice experimentally infected with Rhodococcus equi

Neutrophils are important in controlling early infections with the intracellular bacterium Rhodococcus equi. Antineutrophil monoclonal antibody (RB6-8C5)-induced neutrophil deficiency during the first week after experimental infection of mice with R. equi resulted in more severe disease and significantly increased tissue concentrations of R. equi.

Caprine vertebral osteomyelitis caused by Rhodococcus equi

There have been reports of Rhodococcus equi infections in goats in Australia, America and India. In this study, R. equi was isolated from an inflamed vertebra in a Boer goat in South Africa. At autopsy, there was a purulent inflammatory reaction in the 1st cervical vertebra. Histopathologically, a neutrophilic infiltration was encountered in the bone. Aerobic culture of swabs collected from the abscesses yielded R. equi in pure culture that was identified on biochemical tests. R. equi has become important as the cause of an opportunistic infection in people suffering from HIV.

Evaluation of a multiplex polymerase chain reaction assay for simultaneous detection of Rhodococcus equi and the vapA gene

OBJECTIVE

To evaluate sensitivity and specificity of a multiplex polymerase chain reaction (PCR) assay for simultaneous detection of Rhodococcus equi and differentiation of strains that contain the virulence-associated gene (vapA) from strains that do not.

SAMPLE POPULATION

187 isolates of R equi from equine and nonequine tissue and environmental specimens and 27 isolates of bacterial species genetically or morphologically similar to R equi.

PROCEDURE

The multiplex PCR assay included 3 gene targets: a universal 311-bp bacterial 16S ribosomal RNA amplicon (positive internal control), a 959-bp R equi-specific target in the cholesterol oxidase gene (choE), and a 564-bp amplicon of the vapA gene. Duplicate multiplex PCR assays for these targets and confirmatory singleplex PCR assays for vapA and choE were performed for each R equi isolate. An additional PCR assay was used to examine isolates for the vapB gene.

RESULTS

Results of duplicate multiplex and singleplex PCR assays were correlated in all instances, revealing high specificity and reliability (reproducibility) of the vapA multiplex assay. Of the pulmonary isolates from horses with suspected R equi pneumonia, 97.4% (76/78) yielded positive results for vapA. Seven of 50 (14%) human isolates of R equi yielded positive results for vapA. Six human R equi isolates and 1 porcine isolate yielded positive results for vapB. No isolates with vapA and vapB genes were detected.

CONCLUSIONS AND CLINICAL RELEVANCE

The multiplex PCR assay is a sensitive and specific method for simultaneous confirmation of species identity and detection of the vapA gene. The assay appeared to be a useful tool for microbiologic and epidemiologic diagnosis and research.