MYCOBACTERIUM-AVIUM COMPLEX

Disseminated mycobacterium avium complex spinal osteomyelitis in a patient with interferon gamma receptor deficiency: A case report

Disseminated mycobacterium avium complex (MAC) infection is rare and is classically associated with immunodeficient states. Osteomyelitis is a rare manifestation of disseminated MAC infection. The overwhelming majority of MAC infections occur in patients with human immunodeficiency virus (HIV). Disseminated MAC infection has been described in interferon gamma receptor deficiency, an immunodeficiency mechanistically linked to mycobacterial infection. We present a case of disseminated MAC vertebral osteomyelitis in a patient with interferon gamma receptor deficiency.

Investigation of Mycobacterium avium complex (MAC) in Australian commercial milk using qPCR

This technical research communication describes the first study to use quantitative polymerase chain reaction (qPCR) to investigate the presence of Mycobacterium avium complex (MAC) in Australian pasteurised milk. MAC is the most common NTM responsible for human illnesses and includes M. avium subspecies paratuberculosis (MAP). MAC is a causative agent of lymphadenitis in children, with contaminated food and water considered as a likely source. As such the presence of MAC in milk would have public health significance. MAP has been linked to Crohn's disease and is also the causative agent of Johne's disease in cattle. Previous studies have detected MAP in pasteurised milk from Brazil, India, Czech Republic, USA, Argentina, UK, Iran, Ireland and the United Kingdom. This study investigated a total of 180 commercially available Australian pasteurised milk samples which were tested for MAC DNA in triplicate using PCR. All samples were negative for MAC DNA. An additional 14 milk samples were tested, incubated for 3 weeks at 37 °C to potentially increase the concentration of any viable MAC that may be present and then retested. All samples were again negative for MAC DNA. This could be due to concentrations below the limit of detection, limited sample size or could be reflective of the Australian biosecurity control protocols and surveillance of Johne's disease in ruminant animals.

Structural characterization of CYP144A1 - a cytochrome P450 enzyme expressed from alternative transcripts in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) causes the disease tuberculosis (TB). The virulent Mtb H37Rv strain encodes 20 cytochrome P450 (CYP) enzymes, many of which are implicated in Mtb survival and pathogenicity in the human host. Bioinformatics analysis revealed that CYP144A1 is retained exclusively within the Mycobacterium genus, particularly in species causing human and animal disease. Transcriptomic annotation revealed two possible CYP144A1 start codons, leading to expression of (i) a “full-length” 434 amino acid version (CYP144A1-FLV) and (ii) a “truncated” 404 amino acid version (CYP144A1-TRV). Computational analysis predicted that the extended N-terminal region of CYP144A1-FLV is largely unstructured. CYP144A1 FLV and TRV forms were purified in heme-bound states. Mass spectrometry confirmed production of intact, His₆-tagged forms of CYP144A1-FLV and -TRV, with EPR demonstrating cysteine thiolate coordination of heme iron in both cases. Hydrodynamic analysis indicated that both CYP144A1 forms are monomeric. CYP144A1-TRV was crystallized and the first structure of a CYP144 family P450 protein determined. CYP144A1-TRV has an open structure primed for substrate binding, with a large active site cavity. Our data provide the first evidence that Mtb produces two different forms of CYP144A1 from alternative transcripts, with CYP144A1-TRV generated from a leaderless transcript lacking a 5′-untranslated region and Shine-Dalgarno ribosome binding site.

Rhomboid homologs in mycobacteria: insights from phylogeny and genomic analysis

BACKGROUND

Rhomboids are ubiquitous proteins with diverse functions in all life kingdoms, and are emerging as important factors in the biology of some pathogenic apicomplexa and Providencia stuartii. Although prokaryotic genomes contain one rhomboid, actinobacteria can have two or more copies whose sequences have not been analyzed for the presence putative rhomboid catalytic signatures. We report detailed phylogenetic and genomic analyses devoted to prokaryotic rhomboids of an important genus, Mycobacterium.

RESULTS

Many mycobacterial genomes contained two phylogenetically distinct active rhomboids orthologous to Rv0110 (rhomboid protease 1) and Rv1337 (rhomboid protease 2) of Mycobacterium tuberculosis H37Rv, which were acquired independently. There was a genome-wide conservation and organization of the orthologs of Rv1337 arranged in proximity with glutamate racemase (mur1), while the orthologs of Rv0110 appeared evolutionary unstable and were lost in Mycobacterium leprae and the Mycobacterium avium complex. The orthologs of Rv0110 clustered with eukaryotic rhomboids and contained eukaryotic motifs, suggesting a possible common lineage. A novel nonsense mutation at the Trp73 codon split the rhomboid of Mycobacterium avium subsp. Paratuberculosis into two hypothetical proteins (MAP2425c and MAP2426c) that are identical to MAV_1554 of Mycobacterium avium. Mycobacterial rhomboids contain putative rhomboid catalytic signatures, with the protease active site stabilized by Phenylalanine. The topology and transmembrane helices of the Rv0110 orthologs were similar to those of eukaryotic secretase rhomboids, while those of Rv1337 orthologs were unique. Transcription assays indicated that both mycobacterial rhomboids are possibly expressed.

CONCLUSIONS

Mycobacterial rhomboids are active rhomboid proteases with different evolutionary history. The Rv0110 (rhomboid protease 1) orthologs represent prokaryotic rhomboids whose progenitor may be the ancestors of eukaryotic rhomboids. The Rv1337 (rhomboid protease 2) orthologs appear more stable and are conserved nearly in all mycobacteria, possibly alluding to their importance in mycobacteria. MAP2425c and MAP2426c provide the first evidence for a split homologous rhomboid, contrasting whole orthologs of genetically related species. Although valuable insights to the roles of rhomboids are provided, the data herein only lays a foundation for future investigations for the roles of rhomboids in mycobacteria.

Mycobacterium avium-intracellulare cellulitis occurring with septic arthritis after joint injection: a case report

BACKGROUND

Cellulitis caused by Mycobacterium avium-intracellulare has rarely been described. Mycobacterium avium-intracellulare is a rare cause of septic arthritis after intra-articular injection, though the causative role of injection is difficult to ascertain in such cases.

CASE PRESENTATION

A 57-year-old with rheumatoid arthritis treated with prednisone and azathioprine developed bilateral painful degenerative shoulder arthritis. After corticosteroid injections into both acromioclavicular joints, he developed bilateral cellulitis centered over the injection sites. Skin biopsy showed non-caseating granulomas, and culture grew Mycobacterium avium-intracellulare. Joint aspiration also revealed Mycobacterium avium-intracellulare infection.

CONCLUSION

Although rare, skin and joint infections caused by Mycobacterium avium-intracellulare should be considered in any immunocompromised host, particularly after intra-articular injection. Stains for acid-fast bacilli may be negative in pathologic samples even in the presence of infection; cultures of tissue specimens should always be obtained.

Septic arthritis and granulomatous synovitis caused by infection with Mycobacterium avium complex in a horse

A 12-year-old American Saddlebred gelding was referred to a veterinary teaching hospital for evaluation of a chronic lameness problem in the right radiocarpal joint. The horse had been treated for osteoarthritis of the right radiocarpal joint with multiple injections of cortisone during the past 3 years. The horse was severely lame on the right forelimb at a trot. Radiography and computed tomography revealed a 3 x 2-cm lytic defect in the distal portion of the radius and periarticular bone proliferation around the right radiocarpal joint. Ultrasonography of the distal portion of the radius revealed a soft tissue mass in the palmarolateral aspect of the joint. Proliferative synovium with a large amount of fibrin was observed in the dorsal and palmar aspects of the joint via arthroscopic examination of the right radiocarpal joint. Histologic examination of synovial biopsy specimens revealed proliferative granulomatous synovitis with giant cells. Mycobacterium avium complex was cultured from the synovial fluid. Infection with M avium complex should be considered in horses with chronic recurring arthritis associated with granulomatous synovitis.

Successful treatment of mycobacterium avium osteomyelitis and arthritis in a non-immunocompromised child

In non-immunocompromised children, infections with mycobacterium avium complex (MAC) are rare, except for cervical lymphadenitis. We report here a 34-month-old boy who developed osteomyelitis and septic arthritis due to MAC. No findings could be revealed for immunodeficiency. He was treated successfully for 12 months with combined therapy consisting of clarithromycin, rifabutin and protionamid.

Frequency of abdominal CT findings in AIDS patients with M. avium complex bacteraemia

BACKGROUND

Use of blood culture studies for early diagnosis of Mycobacterium avium complex (MAC) infection has become important due to the recent development of effective antibiotic therapy for this condition. This study assessed the abdominal computed tomography (CT) findings in patients with AIDS who presented with bacteraemic MAC infection.

METHODS

A retrospective analysis of abdominal CT scans was performed in 24 patients who presented with MAC-positive blood culture. CT images were reviewed specifically to evaluate for lymph node enlargement and attenuation, hepatomegaly, splenomegaly, bowel wall abnormality and for any other pathological changes. Comparison was made to prior reports of the CT findings in this disease process.

RESULT

Enlarged intra-abdominal mesenteric and/or retroperitoneal lymph nodes were found in 10 patients (42%). These nodes were characterized by homogeneous, soft-tissue attenuation in eight of the 10 patients. Hepatomegaly, splenomegaly and small bowel wall thickening were noted in 12 (50%), 11 (46%) and four (14%) patients, respectively. CT findings were evaluated as normal in six (25%) patients.

CONCLUSIONS

Enlarged mesenteric and/or retroperitoneal lymph nodes in AIDS patients with bacteraemic MAC were observed much less frequently on CT than previously reported in AIDS patient populations. Normal abdominal CT findings do not exclude this diagnosis and may reflect a trend towards earlier detection of MAC disease.

[Disseminated infection with Mycobacterium avium complex (MAC) in HIV infection]

EPIDEMIOLOGY

Disseminated MAC-infection is one of the most frequent opportunistic infections occurring in HIV-infected patients. Severely immunocompromised patients with CD4-counts < 50/microliter are at greatest risk for the disease. Survival of untreated infection is very poor (5 to 6 months). With therapy survival is prolonged by about 4 months. CLINICAL PRESENTATION AND DIAGNOSTIC PROCEDURES: The leading symptom of MAC-infection is fever eventually accompanied by weight lost, night sweats, enlarged lymph nodes, hepatosplenomegaly, abdominal pain and anemia. Blood cultures are very sensitive and the most appropriate examination. Other diagnostic procedures include bone marrow cultures, biopsies of the gastrointestinal tract, lymph nodes and the liver. Detection of MAC in sputum and stool samples only proves colonisation but not dissemination. However, colonisation of the gastrointestinal tract frequently precedes disseminated disease.

THERAPY

Combination of clarithromycin, rifabutin and ethambutol has proven to be the most efficacious therapy and therefore has to be considered as standard therapy for disseminted MAC-infection. Problems most frequently encountered with this medication include uveitis (rifabutin) gastrointestinal disturbances (clarithromycin) and leucopenia (rifabutin) as well as drug interactions with protease-inhibitors (rifabutin).

PROPHYLAXIS

Clarithromycin, rifabutin and azithromycin given as primary prophylaxis can diminish the risk of disseminated MAC-infection. Although a survival benefit has been seen with clarithromycin, primary prophylaxis of MAC-infection is not standard care in many centers. Reasons to withhold MAC-prophylaxis include lower incidence rates in some countries as well as possible side effects and drug interactions.

CONCLUSION

Disseminated MAC-infection is a frequent opportunistic disease in HIV-infected persons who are severely immunocompromised. Antibiotic combination therapy with clarithromycin, rifabutin and ethambutol improves clinical symptoms and survival. Primary prophylaxis with different regimens is efficacious but the specific epidemiologic situation in each country has to be considered.

Diagnosing HIV-related disease: using the CD4 count as a guide

OBJECTIVE

To summarize current information on the relation between CD4 counts and the risk of different HIV-related diseases.

MEASUREMENTS AND MAIN RESULTS

MEDLINE search of English language articles between 1985 and 1996 using the medical subject heading (MeSH) term "CD4 lymphocyte count" and searches using key words of multiple HIV-related diseases were conducted. Some HIV-related diseases can be stratified to different CD4 count levels. Regardless of their CD4 count, HIV-infected patients are susceptible to sinusitis, Kaposi's sarcoma, community-acquired pneumonia, and oral hairy leukoplakia. In advanced HIV, when CD4 is below 200/mm3, Pneumocystis carinii pneumonia, toxoplasmosis, progressive multifocal leukoencephalopathy, Mycobacterium avium complex, molluscum contagiosum, and bacillary angiomatosis all increase in incidence. In very advanced HIV disease, when CD4 counts are below 50/mm3, patients are at risk of pseudomonas pneumonia, cytomegalovirus retinitis, central nervous system lymphoma, aspergillosis, and disseminated histoplasmosis.