Avium Complex Organisms Research Articles

Mycobacterium avium complex: Adherence as a way of life.

Mycobacterium avium complex (MAC) organisms are waterborne, opportunistic pathogens whose source is natural waters and soils and proliferates and persists in premise plumbing, for example household and hospital plumbing. M. avium complex and other environmental mycobacteria grow slowly, not because their metabolism is slow, but because they synthesize long chain (C60–C80) fatty acids that make up its hydrophobic and impermeable outer membrane. There are costs and benefits to the presence of that lipid-rich outer membrane. One benefit is that cell-surface hydrophobicity drives M. avium complex cells to adhere to surfaces to reduce their interaction with charged ions in suspension; they are likely “biofilm pioneers”, adhering to a wide variety of surface materials. The result is that the slow-growing M. avium complex cells (1 gen/day at 37 °C) will not be washed out of any flowing system, whether a stream or plumbing in the built environment. Although the slow permeation of nutrients in M. avium complex organisms limits growth, they are also resistant to disinfectants, thus increasing their survival in water distribution systems, premise plumbing, and medical equipment. There are three components to the antimicrobial resistance of M. avium complex in biofilms: (1) innate resistance due to the hydrophobic, impermeable outer membrane, (2) residence in a matrix of extracellular polysaccharide, lipid, DNA, and protein that prevents access of antimicrobials to M. avium cells, and (3) an adaptive and transient increased resistance of biofilm-grown M. avium cells grown in biofilms. As expected M. avium in biofilms will display neutral, antagonistic, or beneficial interactions with other biofilm inhabitants. Methylobacterium spp., the common pink-pigmented, waterborne bacteria compete with M. avium for surface binding, suggested an approach to reducing M. avium biofilm formation and hence persistence in premise plumbing.

Mycobacterium avium Complex Disease.

Despite the ubiqitous nature of Mycobacterium avium complex (MAC) organisms in the environment, relatively few of those who are infected develop disease. Thus, some degree of susceptibility due to either underlying lung disease or immunosuppression is required. The frequency of pulmonary MAC disease is increasing in many areas, and the exact reasons are unknown. Isolation of MAC from a respiratory specimen does not necessarily mean that treatment is required, as the decision to treatment requires the synthesis of clinical, radiographic, and microbiologic information as well as a weighing of the risks and benefits for the individual patient. Successful treatment requires a multipronged approach that includes antibiotics, aggressive pulmonary hygiene, and sometimes resection of the diseased lung. A combination of azithromycin, rifampin, and ethambutol administered three times weekly is recommend for nodular bronchiectatic disease, whereas the same regimen may be used for cavitary disease but administered daily and often with inclusion of a parenteral aminoglycoside. Disseminated MAC (DMAC) is almost exclusively seen in patients with late-stage AIDS and can be treated with a macrolide in combination with ethambutol, with or without rifabutin: the most important intervention in this setting is to gain HIV control with the use of potent antiretroviral therapy. Treatment outcomes for many patients with MAC disease remain suboptimal, so new drugs and treatment regimens are greatly needed. Given the high rate of reinfection after cure, one of the greatest needs is a better understanding of where infection occurs and how this can be prevented.

A Case of Hypercalcemia Secondary to Hot Tub Lung

Hypersensitivity pneumonitis (HP) is a diffuse granulomatous lung disease resulting from inhalation of an antigen to which an individual has been previously sensitized. Hot tub lung is an increasingly common form of HP associated with inhalation of water aerosols containingMycobacterium aviumcomplex organisms that contaminate hot tub water. Granulomatous lung disorders, most classically sarcoidosis, have been associated with unregulated 1-α-hydroxylase expression by macrophages present in the granulomas, causing conversion of 25-OH-vitamin D to the active form of vitamin D, 1,25(OH)2 vitamin D, and, thus, hypercalcemia. To our knowledge, this is the first confirmed case of hypercalcemia secondary to elevated 1,25(OH)2 vitamin D levels associated with HP.

Septicemia in Patients With AIDS Admitted to a University Health System: A Case Series of Eighty-Three Patients

Patients with AIDS incur higher rates of infection than the general population. However, little evidence exists to guide family physicians in selecting antibiotics for initial empiric therapy for suspected septicemia. We recorded the causative organisms of septicemia (defined here as bacteremia, fungemia, or both) in 83 patients with AIDS admitted to the teaching hospitals of the University of Louisville from 1996 to 2006. All patients fulfilled the requirements for a diagnosis of AIDS on the basis of the 1993 Centers for Disease Control criteria. In addition to the causative organism, demographic information, immunologic data, portal of entry, and mortality were collected. Only 53% of the patients presented with fever and the median leukocyte count was 4400 cells/mm(3). The most common organisms causing septicemia were, in decreasing order, methicillin-sensitive Staphylococcus aureus (MRSA; n = 21; 21.4%), Mycobacterium avium complex (n = 10; 10.2%), coagulase-negative staphylococci (n = 9; 9.2%) and Streptococcus pneumoniae (n = 9; 9.2%). Other pathogens included Escherichia coli, Pseudomonas aeruginosa, and MRSA. Polymicrobial septicemia was identified in 12 cases (14.5% of the episodes). The portals of entry of the organism were (in decreasing order) primary, lung, intravascular line, and skin. The types of organisms found in patients with primary septicemia patterned those found overall. The mortality rate was 12.1%. AIDS patients with septicemia may not present with the signs that would a non-AIDS patient with septicemia. On the basis of the range of organisms identified in this study, antibiotic coverage of AIDS patients with suspected septicemia, both in primary septicemia and septicemia overall, should take into consideration bacteremia with a wide range of organisms: Gram-positive organisms including MRSA and M. avium complex and Gram-negative organisms including Pseudomonas species. In addition, physicians should be aware that polymicrobial septicemia may be present.

IL-32 expression in the airway epithelial cells of patients with Mycobacterium avium complex lung disease

Lung disease due to Mycobacterium avium complex (MAC) organisms is increasing. A greater understanding of the host immune response to MAC organisms will provide a foundation to develop novel therapies for these recalcitrant infections. IL-32 is a newly described pro-inflammatory cytokine that enhances host immunity against various microbial pathogens. Cytokines that induce IL-32 such as interferon-gamma, IL-18, IL-12 and tumor necrosis factor-alpha are of considerable importance to mycobacterial immunity. We performed immunohistochemistry and morphometric analysis to quantify IL-32 expression in the lungs of 11 patients with MAC lung disease and 10 controls with normal lung tissues. After normalizing for basement membrane length, there was a profound increase in IL-32 expression in the airway epithelial cells of the MAC-infected lungs compared with controls. Following normalization for alveolar surface area, there was a trend toward increased IL-32 expression in type II alveolar cells and alveolar macrophages in the lungs of MAC patients. Human airway epithelial cells (BEAS-2B) infected with M. avium produced IL-32 by a nuclear factor-kappa B-dependent mechanism. In both BEAS-2B cells and human monocyte-derived macrophages, exogenous IL-32γ significantly reduced the growth of intracellular M. avium. This finding was corroborated by an increase in the number of intracellular M. avium recovered from THP-1 monocytes silenced for endogenous IL-32 expression. The anti-mycobacterial effect of IL-32 may be due, in part, to increased apoptosis of infected cells. These findings indicate that IL-32 facilitates host defense against MAC organisms but may also contribute to the airway inflammation associated with MAC pulmonary disease.

Immunogenicity of Proteome-DeterminedMycobacterium aviumsubsp.paratuberculosis-Specific Proteins in Sheep with Paratuberculosis

Mycobacterium avium subsp. paratuberculosis causes paratuberculosis, a chronic granulomatous enteritis. Detecting animals with paratuberculosis infections is difficult because the currently available tools have low sensitivity and lack specificity; these tools are prone to generating spurious positive test results caused by exposure to environmental M. avium complex organisms. To generate candidate antigens for incorporation into a specific test for paratuberculosis, subspecies-specific proteins were determined by proteomic comparison of M. avium subsp. paratuberculosis and M. avium subsp. avium. Analysis was aimed at revealing proteins only expressed (or predominant) in the protein profile of M. avium subspecies paratuberculosis. Two-dimensional gel electrophoresis resolved approximately 1,000 protein spots from each subspecies. Proteome analysis identified protein spots whose expression profile appeared markedly increased in M. avium subsp. paratuberculosis, and 32 were identified by analysis of their tryptic peptide profile by matrix-assisted laser desorption ionization-time of flight analysis. Thirty of these proteins were cloned, and their recombinant proteins were expressed. Ovine paratuberculosis sera were used to assess their immunoreactivity by enzyme-linked immunosorbent assay (ELISA), Western blotting, and dot blot analysis. Seventeen proteins were detected in at least one of the immunoassays, and eleven proteins were detected by ELISA with an optical density in excess of the cutoff of 0.1 in four of six sera tested. The immunoreactivity of these proteins indicates their potential as unique diagnostic antigens for the development of a specific serological detection of paratuberculosis.

Genetic diversity of Mycobacterium avium isolates recovered from clinical samples and from the environment: molecular characterization for diagnostic purposes.

Isolation of Mycobacterium avium complex (MAC) organisms from clinical samples may occur in patients without clinical disease, making the interpretation of results difficult. The clinical relevance of MAC isolates from different types of clinical samples (n = 47) from 39 patients in different sections of a hospital was assessed by comparison with environmental isolates (n = 17) from the hospital. Various methods for identification and typing (commercial probes, phenotypic characteristics, PCR for detection of IS1245 and IS901, sequencing of the hsp65 gene, and pulsed-field gel electrophoresis) were evaluated. The same strain was found in all the environmental isolates, 21 out of 23 (91.3%) of the isolates cultured from urine samples, and 5 out of 19 (26.3%) isolates from respiratory specimens. This strain did not cause disease in the patients. Testing best characterized the strain as M. avium subsp. hominissuis, with the unusual feature that 81.4% of these isolates lacked the IS1245 element. Contamination of certain clinical samples with an environmental strain was the most likely event; therefore, characterization of the environmental mycobacteria present in health care facilities should be performed to discard false-positive isolations in nonsterile samples, mainly urine samples. Molecular techniques applied in this study demonstrated their usefulness for this purpose.

CT Findings of Granulomatous Pneumonitis Secondary to Mycobacterium avium-intracellulare Inhalation: “Hot Tub Lung”

The objective of our study was to describe the CT features of "hot tub lung" caused by exposure to Mycobacterium avium complex (MAC) organisms in contaminated water. Chart review was performed to identify all patients with a histologic diagnosis of granulomatous pneumonitis and positive cultures for MAC between January 1, 1995, and July 1, 2004. Individuals identified who also had a hot tub were included in the study. Twelve patients, seven females and five males with an average age of 50 years (range, 13-66 years), who had a CT scan were identified. The CT images were reviewed by two thoracic radiologists who assessed the images for the presence of any parenchymal abnormalities, including nodules, areas of ground-glass attenuation, reticular opacities, and air trapping, on expiratory images. When nodules, reticular opacities, areas of ground-glass attenuation, or a combination of these findings was present, the reviewers visually determined the extent of involvement of the lungs using a scale of < 10%, 10-40%, or > 40%. They also recorded the distribution of the involvement both cephalocaudal and transaxial. Decisions were reached by consensus of the reviewers. Nodules were present in 10 (83%) of 12 patients. In eight (80%) of 10 patients, the nodules were diffuse with a centrilobular distribution. In the other two, the nodules were randomly distributed with an upper lung predominance. In five patients the nodules showed areas of ground-glass attenuation, whereas in the other five the nodules were solid. Areas of ground-glass attenuation were present in eight (75%) of 12 patients and were bilateral in all cases. The areas of ground-glass attenuation were diffuse in the cephalocaudal plane with a random distribution in the transaxial plane in seven (88%) of eight cases. In the remaining case, the areas of ground-glass attenuation had a lower lung predominance with a random distribution in the transaxial plane. Expiratory images showed evidence of air trapping in all seven cases for which these images were available. In one patient, air trapping was the only abnormality identified. The CT findings in patients with hot tub lung include areas of ground-glass attenuation, centrilobular nodules, and air trapping on expiratory images. These findings are similar to previously published findings of subacute hypersensitivity pneumonitis. Therefore, in cases in which CT findings suggest hypersensitivity pneumonitis, hot tub lung should also be a diagnostic consideration.

Genetic Analysis ofMycobacterium aviumComplex Strains Used for Producing Purified Protein Derivatives

For over a century, purified protein derivatives (PPD) have been used to detect mycobacterial infections in humans and livestock. Among these, reagents to detect infections by Mycobacterium avium complex organisms have been produced, but the utility of these reagents has not been clearly established due in part to limited biologic and immunologic standardization. Because there is little information about the strains used to produce these reagents (avian PPD, intracellulare PPD, scrofulaceum PPD, and Johnin), we have performed genetic characterizations of strains used to produce these products. Sequence analysis of 16S rRNA and the hsp65 gene provided results concordant with species designations provided for M. avium, Mycobacterium intracellulare, and Mycobacterium scrofulaceum organisms. For M. avium strains, comparative genomic hybridization was performed on a whole-genome DNA microarray, revealing one novel 7.9-kilobase genomic deletion in certain Johnin-producing strains, in addition to genomic variability inherent to the particular M. avium subspecies. Our findings indicate that considerable genomic differences exist between organisms used for reagents and the infecting organism being studied. These results serve as a baseline for potency studies of different preparations and should aid in comparative studies of newly discovered antigens for the diagnosis of infection and disease by M. avium complex organisms.

Hot tub lung: Presenting features and clinical course of 21 patients

Hot tub lung is an emerging lung disorder associated with exposure to Mycobacterium avium complex organisms contaminating hot tub water. To define the clinical characteristics and outcome of patients with hot tub lung. Retrospective review of 21 patients diagnosed with hot tub lung at a tertiary medical center over a 7-year period. The mean (+/-sd) age at presentation was 46 (+/- 15) years; 9 patients were men (43%). All patients described ongoing exposure to hot tubs. The most common referral diagnoses were sarcoidosis, bronchitis, and asthma. Dyspnea and cough were present in all patients, hypoxemia was noted in 10 patients (48%). High-resolution computed tomography of the chest had been performed in 20 patients and demonstrated diffuse centrilobular nodules and/or ground-glass opacities in all patients. M. avium complex was isolated from the hot tub water, respiratory secretions and/or lung tissue in all patients. Bronchoscopic or surgical lung biopsy was obtained in 18 patients and demonstrated bronchiolocentric granulomatous inflammation. With avoidance of exposure, clinical and radiologic improvement was observed in all patients. Additionally, 13 patients (62%) received corticosteroid therapy, 1 (5%) antimycobacterial therapy, 2 (10%) received both, and 5 patients (24%) received no pharmacologic therapy. Hot tub lung likely represents hypersensitivity pneumonitis due to inhalational exposure to M. avium complex. Antimycobacterial therapy does not appear to be required in the management of this disease. Although corticosteroids may be helpful in the treatment of severely affected patients, others can be managed by avoidance of additional exposure alone.

Electrophoretic Mobility of Mycobacterium avium Complex Organisms.

The electrophoretic mobilities (EPMs) of 30 Mycobacterium avium complex organisms were measured. The EPMs of 15 clinical isolates ranged from -1.9 to -5.0 microM cm V(-1) s(-1), and the EPMs of 15 environmental isolates ranged from -1.9 to -4.6 microM cm V(-1) s(-1) at pH 7.

Hospital water as a source of Mycobacterium avium complex isolates in respiratory specimens.

The clinical significance of recovery of Mycobacterium avium complex (MAC) organisms from respiratory specimens is poorly understood. One hundred sixty-one respiratory MAC isolates from 131 patients at Grady Memorial Hospital (Atlanta) and 13 MAC isolates from the hospital's hot water system were examined. Of the 131 patients, 35 (27%) had MAC disease, and 96 (73%) did not; 94 (72%) were human immunodeficiency virus infected. Ten different clusters were identified by pulsed-field gel electrophoresis. Patients without MAC disease were significantly more likely to have clustered isolates than were patients with MAC disease. Of 110 MAC isolates recovered from patients without MAC disease, 72 (65%) were part of a single large cluster that contained isolates recovered from the hospital's hot water system; 13 (25%) of 51 isolates from patients with MAC disease were also in this cluster. We conclude that acquisition of MAC from institutional water systems leads to substantial MAC disease but that most patients with MAC recovered from respiratory specimens have only transient colonization by MAC.

Hot tub lung: infection, inflammation, or both?

Increasing numbers of patients have presented with a hypersensitivity pneumonitis-type course in association with hot tub exposure. Mycobacterium avium complex (MAC) organisms have been isolated from both patient specimens and hot tub water with matching fingerprints by restricted fragment length polymorphism and electrophoresis when performed. Review of the clinical, microbiologic, and radiographic presentations of 9 patients to the Mayo Clinic with this diagnosis are compared with 32 patients in the published literature. The diagnosis, treatment, and prognosis of MAC hot tub lung are reviewed.

Mycobacterium Avium Complex Hot Tub Lung: Infection, Inflammation, or Both

PURPOSE: Increasing numbers of patients have presented with a hypersensitivity pneumonitis-type course in association with hot tub exposure. Mycobacterium avium complex (MAC) organisms have been isolated from both patient specimens and hot tub water with matching fingerprints by restricted fragment length polymorphism and electrophoresis when performed. Review of 9 patients at Mayo Clinic, Rochester are compared with 32 patients in the published literature (reference patients).

Association of DRB1*1501 with disseminated Mycobacterium avium complex infection in North American AIDS patients.

The HLA class II allele, DR2 (DRB1*1501), has been repeatedly found to be associated with development of tuberculosis and leprosy. We searched for associations of these and other class II alleles with disseminated Mycobacterium avium complex infection (DMAC) in North American Caucasian homosexual AIDS patients. Molecular typing for HLA-DRB1 and -DQB1 alleles in 176 cases of DMAC and 176 matched controls showed an association of accelerated onset of disease with DRB1*1501 (and the closely linked DQB1*0602) that was stronger upon adjustment for the degree and duration of CD4+ cell deficiency (P=0.04) and in multivariate analysis (P=0.02) than in unadjusted analysis. A similar trend was seen with DRB1*0701, and no other allele showed a relationship of similar magnitude. M. avium complex organisms may more effectively evade host defenses in individuals carrying an HLA polymorphism identical to that associated with M. tuberculosis and M. leprae.

The pathophysiology of disseminated Mycobacterium avium complex disease in AIDS.

Mycobacterium avium complex (MAC) organisms cause disseminated disease in patients with AIDS. The organisms penetrate the gastrointestinal mucosa by unknown mechanisms and are phagocytosed by macrophages in the lamina propria. These cells cannot kill the organisms, and MAC spreads through the submucosal tissue. Lymphatic drainage transports mycobacteria to abdominal lymph nodes, from which the organisms enter the bloodstream. Hematogenous spread can occur to many sites, but spleen, bone marrow, and liver are the most common. Tissue destruction is rare, and most signs and symptoms of MAC disease are due to elaboration of cytokines. MAC is rarely the direct cause of death but increases the risk for superinfection; death may result from malnutrition or other infections.

Analysis of Mycobacterium avium complex serovars isolated from AIDS patients from southeast Brazil.

The purpose of this study was to assess the distribution of Mycobacterium avium serovars isolated from AIDS patients in São Paulo and Rio de Janeiro. Ninety single site or multiple site isolates from 75 patients were examined. The most frequent serovars found were 8 (39.2%), 4 (21.4%) and 1 (10.7%). The frequency of mixed infections with serovar 8 or 4 was 37.8%. Among the 90 strains examined, M. intracellulare serovars (7 strains) and M. scrofulaceum (4 strains) were found in 11 isolates (12%) indicating that M. avium (88%) was the major opportunistic species in the M. avium complex isolates in Brazilian AIDS patients.

Increased Lung Cell Cytotoxic but Not Bactericidal or Phagocytic Activity inMycobacterium aviumComplex-Infected Mice

Following intranasal infection of mice withMycobacterium aviumcomplex (MAC) organisms, bacterial growth plateaued at the fourth week postinfection and then remained relatively constant thereafter. Inflammatory cell numbers in the lungs increased 10-fold by 4 weeks postinfection, and lung cell cytotoxicity and the production of NO, H2O2, and O−2by lung cell cultures had all increased significantly by this time and remained elevated throughout the 15-week experimental study. Although these parameters are generally associated with increased bactericidal activity, there appeared to be a defect in phagocytosis by lung cells, so that bactericidal activity could not be demonstrated in eitherin vitroorin vivoexperiments. This study suggests that following intranasal infection with MAC, inflammatory cells are activated, sufficient to prevent further bacterial growthin vivobut not sufficient to clear the infection. We suggest that the deficiency may lie in the phagocytic activity of the cells.

Isolation and characteristics of Mycobacterium avium complex from water and soil samples in Uganda

Setting: Mycobacterium avium complex organisms have not been isolated from late stage AIDS patients in Uganda. This could possibly be due to the absence of M. avium complex in the Uganda environment. Objective and Design: Determine whether M. avium complex organisms could be isolated from water and soils collected in the living environment of Ugandan AIDS patients. Results: Representatives of the M. avium complex were isolated from 3 of 7 (43%) water and 3 of 7 (43%) soil samples collected in Kampala, Uganda. The average number of colony-forming units per ml water was 3.3 and average colony-forming units per gram of soil was 7825. In terms of growth characteristics, antimicrobial susceptibility patterns, and the presence or absence of plasmids and IS 901, Ugandan M. avium complex isolates were similar to those isolated from the US and European AIDS patients and their environment. Conclusion: M. avium complex organisms sharing genetic and physiological characteristics of M. avium complex isolates recovered from patients with AIDS can be isolated from water and soil samples in Uganda.

Rapid induction of mRNA for nitric oxide synthase II in rat alveolar macrophages by intratracheal administration of Mycobacterium tuberculosis and Mycobacterium avium.

Mycobacterium avium complex (MAC) organisms are among the most common bacterial cause of disseminated infection in patients with acquired immune deficiency syndrome (AIDS). An increase in the incidence of virulent Mycobacterium tuberculosis (MTB) is also occurring throughout the world. In vitro data suggest that nitric oxide (NO) may be important in restricting the growth of MAC. However, the ability of MTB to stimulate NO production and the susceptibility of MTB to the bactericidal activity of NO produced by murine alveolar macrophages (AM) is controversial. This study tested the hypothesis that in vivo administration of heat-killed MAC (strain 100 and 101) and human virulent MTB (strain F1) to rats stimulated NO production by rat AM, ex vivo. We show that heat-killed MTB instilled into rat lungs rapidly induced mRNA for NO synthase (iNOS) II in AM obtained by bronchoalveolar lavage (BAL). In contrast, expression of AM iNOS mRNA was only found in 40% of the rats given MAC. Moreover, the change in iNOS mRNA in the AM obtained from rats given MTB and MAC correlated with the production of the reactive nitrogen intermediates (RNI) NO2- and NO3- in BAL fluid, lung homogenate, and the spontaneous generation of RNI by isolated AM ex vivo and occurred without measurable increases in BAL fluid tumor necrosis factor-alpha (TNF-alpha). L-NG-monomethylarginine (50 mg/kg, ip) given 30 min before MAC or MTB attenuated the increase in RNI in lung homogenates and BAL fluid. This is the first demonstration that in vivo exposure to MTB results in rapid upregulation of gene expression for iNOS which is associated with functional RNI production by rat AM. These results show that MTB human virulent strain 1 has the ability to rapidly upregulate iNOS mRNA in AM. If human AM generate NO from L-arginine by either iNOS or other NADPH oxidases then NO may play a role in the overall host-defense response of the lung to MAC and MTB.