Mycobacterium avium complex infection in HIV/AIDS patients

Disseminated Mycobacterium avium complex (MAC) infection is a severe complication of advanced HIV/AIDS disease. Disseminated infection due to MAC appeared later in the natural history of HIV disease and was an independent predictor of mortality in patients before the extended use of highly active antiretroviral therapy (HAART). The use of combination schemes, including three or four antimicrobial agents followed by secondary prophylaxis and HAARTs, improved the survival and reduced mortality rates. However, subjects who ignore their serological status for HIV, or who are not receiving or do not tolerate HAART, are at high risk of developing disseminated MAC disease. In addition, patients who show a good immunological and virological response to HAART can develop episodes of immune reconstitution inflammatory syndrome associated with MAC, including supurative lymphadenitis and subcutaneous or soft-tissue abscesses. In this article, we describe the epidemiological, clinical, immunological, therapeutic and preventive aspects of MAC infection in HIV-seropositive patients in the pre- and post-HAART era.     

Non-radioactive DNA probe for the rapid identification of Mycobacterium avium complex from clinical specimens.

We evaluated an alkaline phosphatase labelled oligonucleotide probe (SNAP(TM), Syngene Co., Molecular Biosystems, Inc., San Diego CA) for the direct culture identification of Mycobacterium avium complex (MAC) isolated from clinical specimens. Mycobacterial species identified by conventional biochemical methods were retested with this DNA probe using the Centri-Dot(TM) format. The probe accurately identified all 69 pigmented M. avium complex and 15 non-pigmented isolates of M. avium complex. There were no false-positives with 45 non-MAC mycobacteria isolates (10 species) and 16 non-mycobacteria organisms (10 species). The sensitivity and specificity of the SNAP(TM) culture identification for M. avium complex were 100%. The alkaline phosphatase labelled DNA probe is stable for at least 9 months. The procedure can be completed within 2 h and is easily adapted in the clinical laboratory. For the strains encountered in our laboratory, we conclude that the SNAP(TM) hybridization is a rapid, specific, and reliable method for culture identification of M. avium complex.     

Azithromycin as treatment for disseminated Mycobacterium avium complex in AIDS patients

This multicenter, randomized, dose-ranging study was performed to determine the safety and efficacy of two different doses of azithromycin for treating disseminated Mycobacterium avium complex (MAC) in patients with AIDS. Eighty-eight AIDS patients with symptoms and blood cultures consistent with disseminated MAC were treated with 600 or 1,200 mg of azithromycin daily for 6 weeks; 62 patients completed the entire 6 weeks of study. Of note, this study was done prior to the time when combination antiretroviral or anti-MAC regimens were the standard of care. Over the 6-week study period, symptomatic improvement was noted in both dose groups. Microbiological responses were comparable, with mean decreases of 1. 5 and 2.0 log CFU/ml in the high- and low-dose groups, respectively. Sterilization of blood cultures occurred in 54% of samples; patients with lower baseline colony counts were more likely to achieve culture negativity. Resistance developed in one patient. Gastrointestinal symptoms were the most common side effects and were more frequent in patients receiving 1,200 mg. Azithromycin is a useful alternative treatment for disseminated MAC infection in AIDS patients. Symptomatic improvement correlates with measurable decreases in mycobacterial load.     

Disseminated disease due to Mycobacterium avium complex in AIDS

We retrospectively analysed 46 cases of disseminated infectionwith Mycobacterium avium complex (MAC) within a cohort of 702HIV-infected patients in Edinburgh. Clinical features were comparedwith case-matched controls (AIDS cases without disseminatedMAC), and survival and progression times were controlled forconfounding variables that influence survival. DisseminatedMAC was diagnosed antemortem in 18% of AIDS patients, and wasthe AIDS-defining diagnosis in 6% of all AIDS cases. Concomitantcolonization of respiratory and gastrointestinal tracts wascommon (61% and 48%, respectively). In 58% of cases, CD4 + countswere <10 cells/mm³ (median 6 cells/mm³). Weight loss, anaemia,leucopenia, and elevated liver transaminases and alkaline phosphatasewere significantly more common among cases than controls. Therapywas given in 74%, and not tolerated in 32%. Following AIDS diagnosis,disseminated MAC incidence was 14% at one year, 25% at 2 yearsand 36% at 3 years. Median survival after disseminated MAC diagnosiswas 6 months, with shorter survival in untreated cases. However,overall survival from AIDS diagnosis was not significantly differentbetween patients who did or did not develop disseminated MAC.Disseminated MAC contributes significantly to AIDS morbidity,and its incidence increases with prolonged AIDS survival. Althoughsurvival following diagnosis is short, the development of disseminatedMAC in AIDS probably does not affect overall survival. In cohortswith a low incidence, an alternative to prophylaxis might besurveillance and early diagnosis.     

Relationship between clinical efficacy of treatment of pulmonary Mycobacterium avium complex disease and drug-sensitivity testing of Mycobacterium avium complex isolates

We prospectively investigated the relationship between the clinical efficacy of treatment of pulmonary Mycobacterium avium complex (MAC) disease and drug-sensitivity testing of MAC isolates for antituberculous drugs, new quinolone antibiotics, and clarithromycin (CAM). Fifty-two patients who satisfied the diagnostic criteria of the American Thoracic Society (ATS) and who received treatment between April 1998 and December 2005, using combined therapy of rifampicin (RFP), ethambutol (EB), streptomycin (SM), and CAM, were enrolled in this study. The causative microorganisms isolated were Mycobacterium avium in 30 patients and M. intracellulare in 22 patients. Although separation of the two strains showed drug sensitivity testing to have slightly better minimal inhibitory concentrations (MIC) for M. intracellulare than for M. avium, there were no significant differences in the sputum eradication rate or clinical improvement between the two strains. The MICs of various antibiotics for the isolated MAC strains were as follows: RFP, 0.125–8 μg/ml; CAM, 0.25–16 μg/ml; SM, 2–128≦ μg/ml; EB, 128≦ μg/ml; levofloxacin (LVFX), 1–32 μg/ml; sparfloxacin (SPFX), 0.5–16 μg/ml; and gatifloxacin (GFLX), 0.25–8 μg/ml. The isolated MAC strains showed the same excellent drug sensitivity test results for RFP, new quinolones, and CAM, but they showed resistant drug-sensitivity results for EB and SM. Regarding the relationship between clinical efficacy and the MICs of RFP, EB, CAM, and SM, there was a good relationship only for CAM. Although the ATS has not yet recommended routine drug susceptibility testing of CAM, we believe that drug susceptibility testing of CAM should be performed before the initial treatment is undertaken for pulmonary MAC disease.     

Mycobacterium avium complex pulmonary disease in immunocompetent patients

Mycobacterium avium complex is becoming increasingly recognized as one of the most common mycobacterial pathogens in humans. It is rapidly becoming a significant cause of pulmonary disease even in those with an intact immunity. In 1997, the American Thoracic Society published recommendations for the diagnosis and treatment of nontuberculous mycobacteria. On the basis of the authors' clinical experience of the myriad presentations of pulmonary Mycobacterium avium complex disease in an immunocompetent host, a clinical classification is proposed. The current data are summarized, and a practical approach to management of the various pulmonary forms of the disease is provided.     

Low-dose dexamethasone as adjunctive therapy for disseminated Mycobacterium avium complex infections in AIDS patients.

Five human immunodeficiency virus-infected patients with disseminated Mycobacterium avium complex infection had progressive weight loss and persistent fever despite multidrug antimycobacterial therapy. These patients were given daily low-dose oral dexamethasone (typically 2 mg/day) as adjunctive therapy. All had substantial and sustained weight gain (12 to 50% of pre-steroid treatment body weight [P < 0.03]), reduction in fever, and an improved sense of well-being. The serum albumin level increased during dexamethasone therapy (from 3.06 +/- 0.59 g/dl [mean +/- standard deviation] to 3.9 +/- 0.22 g/dl [P < 0.01]), while the serum alkaline phosphatase level fell (from 368 +/- 247 U/liter to 128 +/- 43.6 U/liter [P < 0.04]). Further studies of the potential role for corticosteroids in the management of disseminated M. avium complex infections in human immunodeficiency virus-infected patients are warranted.     

Effects of surface-active agents on drug susceptibility levels and ultrastructure of Mycobacterium avium complex organisms isolated from AIDS patients

The multiple-drug-resistance property of Mycobacterium avium complex (MAC) is mainly attributed to a cell envelope permeability barrier. MAC treated with subinhibitory levels of dimethyl sulfoxide (DMSO) and ethylenediaminetetraacetic acid (disodium salt) (EDTA) did not have altered minimum inhibitory concentration (MIC) levels or show ultrastructural changes; the effect of sodium dodecyl sulfate (SDS) was variable. With SDS, the visualization of the nucleoid and ribosomes decreased, and amorphous electron-dense material accumulated near the structurally altered cytoplasmic membrane and cell wall. Use of 0.005% Tween-80 resulted in a 2-4-fold reduction in MIC in the case of rifampicin, ansamycin (LM 427), cephapirin, and ciprofloxacin. Tween-80 treated cells were swollen, and deposits of low electron-density accumulated in the cytoplasm; distortions in the outer-cell integuments were observed. These findings are consistent with the idea that Tween-80 increases cell-envelope permeability, thereby enhancing drug penetrability and reducing MIC levels. Because of the action of Tween-80, its use in drug-susceptibility media or diluent fluids should be avoided.     

Evaluation of Syngene DNA-DNA probe assays for the identification of the Mycobacterium tuberculosis complex and the Mycobacterium avium complex.

Two hundred mycobacterial cultures were used to evaluate two alkaline-phosphatase-labeled DNA probe (SNAP) kits developed by Syngene (San Diego, CA) for identification of Mycobacterium tuberculosis complex and M. avium complex. The M. tuberculosis complex SNAP probe, when compared with standard biochemical identification tests, gave results that were in agreement at 100% sensitivity and 98.7% specificity. Ninety-nine M. avium complex strains that were previously tested by the Gen-Probe M. avium complex probe assays and mycolic acid analysis were included to evaluate the M. avium complex SNAP assay which contained three probes, A (avium), I (intracellulare), and X. Eight strains identified as members of the M. avium complex by biochemical tests did not react with the three SNAP probes. These strains were also negative by the Gen-Probe assays. However, 23 strains identified as M. avium complex by biochemical tests and mycolic acid analysis and negative with the Gen-Probe assays gave positive results with the X probe and negative results with the A and I probes of the SNAP assay.     

Characteristics of patients with bronchoscopy-diagnosed pulmonary Mycobacterium avium complex infection

Background

We occasionally treat patients with clinically suspected pulmonary Mycobacterium avium complex (MAC) infection and negative MAC culture on bronchoscopy.

Comparative in-vitro activity of twenty antimicrobial agents against clinical isolates of Mycobacterium avium complex

The in-vitro susceptibility of Mycobacterium avium complex isolates, obtained from immunosuppressed patients with and without the Acquired Immunodeficiency Syndrome (AIDS), to various antimicrobial agents was determined. Amikacin, the 4-quinolone compounds--ciprofloxacin, temafloxacin and PD 117558--and the penem SCH 34343 were active against most of the isolates. In-vitro synergism using selected antimicrobial combinations could not be demonstrated. No differences in the susceptibility, depending upon the source of the isolates (AIDS or non-AIDS), were noted.     

Evaluation of microplate Alamar blue assay for drug susceptibility testing of Mycobacterium avium complex isolates

Fifty-one clinical isolates and 5 clarithromycin-resistant mutants of Mycobacterium avium complex (MAC) were tested for their susceptibility to clarithromycin by microplate Alamar blue assay (MABA). The susceptibility results were compared with the results obtained by the BACTEC 460 method. All clinical isolates were susceptible, while all mutants were resistant to clarithromycin by BACTEC. Eighty-six percent of the clinical isolates were susceptible by MABA, and one of the resistant mutants was misclassified as susceptible by this method. The overall agreement between MABA and BACTEC was 86%, indicating the usefulness of MABA in drug susceptibility testing of MAC.     

Isolation and characterizations of clarithromycin-resistant Mycobacterium avium clinical isolates

Mycobacterium avium is an important intracellular pathogen, particularly in AIDS patients. It also shows the second frequency among nontuberculous mycobacteria infections in Korea. Point mutations of domain V region of the 23S rRNA gene has been known to confer clarithromycin resistance to M. avium. In order to isolate the clarithromycin-resistant strains from clinical isolates of M. avium and characterize them, we isolated the clarithromycin-resistant strains from clinical isolates of M. avium using reverse hybridization assay (RHA) and broth microdilution test (BMT). Three clarithromycin-resistant isolates with high level of MICs were found from 274 clinical isolates by BMT. Two of three resistant strains were also found by RHA, which revealed point mutations in the domain V region of the 23S rRNA. We report here clarithromycin-resistant clinical isolates of M. avium with the different characteristics from those of the resistant strains reported from earlier studies.     

Occurrence of the IS900 gene in Mycobacterium avium complex derived from HIV patients.

The occurrence of the insertion sequence IS900 in Mycobacterium avium subsp. avium strains isolated from HIV infected patients has been investigated. In this study, genomic DNA from 62 mycobacterial isolates [31 strains of M. avium complex (MAC) consisting of 26 M. avium subsp. avium HIV-isolates and five non-HIV isolates and 31 additional Mycobacterium species] were analysed by an IS900 -based polymerase chain reaction (PCR) assay and Southern hybridization using a non-radioactive-labelled 251 bp DNA fragment located at the 5'-region of the IS900 sequence. As expected, none of the 28 Mycobacterium species contained the IS900 in their genomic DNA. Of the 26 M. avium subsp. avium HIV-isolates, 15 (57.6%) were strongly positive for the IS900 or IS900 related sequence. The five pulmonary non-HIV MAC isolates were negative for the IS900. As expected, the three strains of M. avium subsp. paratuberculosis were positive. This PCR guided study suggest that the IS900 gene is very common in clinical strains of M. avium subsp. avium especially those isolated from HIV patients. Ultimately the IS900 PCR-based assay may provide a useful tool for diagnostic and epidemiological studies related to MAC infections in HIV patients.     

Mycobacterial interspersed repetitive units (MIRU) differentiate Mycobacterium avium subspecies paratuberculosis from other species of the Mycobacterium avium complex

Mycobacterial interspersed repetitive units (MIRU) comprise short tandem repeat structures found at multiple loci throughout the Mycobacterium tuberculosis genome and have been used for typing these pathogens. We have identified MIRU at 18 conserved loci throughout the common portions of the Mycobacterium avium subspecies paratuberculosis (MAP) and M. avium subspecies avium (MAA) genomes. Six of these loci were found to differ between MAA and MAP in the number of tandem repeat motifs occurring at each MIRU locus. Locus specific PCR at 4 of these loci segregated MAP into two major groups, which could be differentiated from ovine-pigmented strains of MAP and the MAP vaccine strain 316F. The same PCR differentiated MAA into five MIRU profiles. PCR at either MIRU locus 1 or MIRU locus 4 distinguished between MAP and all other M. avium complex (MAC) tested. PCR at both loci 1 and 4 also distinguished MAP from Mycobacterium intracellulare. MIRU typing may provide an additional simple and rapid procedure for the differentiation between MAP and other MAC.     

Moxifloxacin resistance and genotyping of Mycobacterium avium and Mycobacterium intracellulare isolates in Japan

BackgroundAlthough fluoroquinolones are considered as alternative therapies of pulmonary Mycobacterium avium complex (MAC) disease, the association between fluoroquinolone resistance and MAC genotypes in clinical isolates from individuals not previously treated for MAC infection is not fully clear.MethodsTotals of 154 M. avium isolates and 35 Mycobacterium intracellulare isolates were obtained from treatment-naïve patients with pulmonary MAC disease at the diagnosis of MAC infection at 8 hospitals in Japan. Their susceptibilities of moxifloxacin were determined by broth microdilution methods. Moxifloxacin-resistant isolates were examined for mutations of gyrA and gyrB. Variable numbers of tandem repeats (VNTR) assay was performed using 15 M. avium VNTR loci and 16 M. intracellulare VNTR loci.ResultsMoxifloxacin susceptibility was categorized as resistant and intermediate for 6.5% and 16.9%, respectively, of M. avium isolates and 8.6% and 17.1% of M. intracellulare isolates. Although the isolates of both species had amino acid substitutions of Thr 96 and Thr 522 at the sites corresponding to Ser 95 in the M. tuberculosis GyrA and Gly 520 in the M. tuberculosis GyrB, respectively, these substitutions were observed irrespective of susceptibility and did not confer resistance. The VNTR assays showed revealed three clusters among M. avium isolates and two clusters among M. intracellulare isolates. No significant differences in moxifloxacin resistance were observed among these clusters.ConclusionsAlthough resistance or intermediate resistance to moxifloxacin was observed in approximately one-fourth of M. avium and M. intracellulare isolates, this resistance was not associated with mutations in gyrA and gyrB or with VNTR genotypes.     

Surgical treatment of Mycobacterium avium complex lung disease

Mycobacterium avium complex (MAC) lung disease is the most common nontuberculous mycobacterial lung disease in Japan and is difficult to treat. Multidrug regimen employing clarithromycin, rifampicin, and ethambutol is not a panacea. Pulmonary resection may be beneficial to patients whose disease is predominantly localized to one lung and who can tolerate resectional surgery under the following circumstances: poor response to drug therapy, the development of macrolide-resistant MAC disease, or the presence of hemoptysis. Resectional surgery for MAC lung disease can achieve favorable treatment outcome. However, this type of surgery is associated with a relatively high morbidity and should be performed by experienced hands.