Comparison of virulence of Mycobacterium avium complex (MAC) strains isolated from AIDS and non-AIDS patients

Mycobacterium avium complex (MAC) strains from AIDS and non-AIDS patients and from the environment were studied for their colony morphology and virulence in beige mice. The majority of the MAC isolates from AIDS patients, in contrast to those from non-AIDS patients and the environment, showed increased virulence. Similarly, the majority of the MAC isolates from AIDS patients formed smooth transparent (ST) colonies, whereas most of the non-AIDS isolates formed smooth opaque (SO) or intermediate (IM) type of colonies. MAC isolates from the same AIDS patient obtained at different times were found to be heterogenic with respect to serotype, RFLP and glycolipid patterns, suggesting that these patients might be infected with more than one strain of MAC.

Mycobacterium avium complex in the respiratory or gastrointestinal tract and the risk of M. avium complex bacteremia in patients with human immunodeficiency virus infection

Mycobacterium avium complex (MAC) is frequently isolated from the respiratory or gastrointestinal tract of patients with advanced human immunodeficiency virus (HIV) infection. Whether they are at increased risk of MAC bacteremia and whether culture of respiratory tract or stool specimens is useful for predicting bacteremia are unclear. HIV-infected patients with < or = 50 CD4+ cells/microL were prospectively studied. The risk of MAC bacteremia was approximately 60% within 1 year for patients with MAC in either the respiratory or gastrointestinal tract and was greater than for those without MAC in these sites (relative hazards for respiratory and gastrointestinal tract, 2.3 and 6.0; 95% confidence intervals, 1.1-4.6 and 2.5-14.6, respectively). Both respiratory tract specimen and stool culture had poor sensitivities (22% and 20%, respectively) but good positive predictive values (approximately 60%) for bacteremia. Symptomatic HIV-infected patients with MAC in the respiratory or gastrointestinal tract are at a substantial risk for developing MAC bacteremia; culture of these sites has limited usefulness as a screening test.

Potential role of cytokines in disseminated mycobacterial infections

Organisms belonging to the Mycobacterium avium complex (MAC) are common pathogens in immunosuppressed and AIDS patients. This paper reviews the role of cytokines in the pathogenesis of MAC infection. MAC organisms mainly infect monocytes and macrophages, and the effect of HIV infection on susceptibility of macrophages to MAC infection is largely unknown. Both GM-CSF and tumour necrosis factor-alpha can induce mycobacteriostatic/mycobactericidal activity in MAC-infected macrophages. The activity of interferon-gamma on mycobacterial infection appears to be dependent on the type of macrophage: in murine peritoneal and human monocyte-derived macrophages, interferon-gamma does not inhibit the intracellular growth of MAC, whereas in intestinal macrophages interferon-gamma results in inhibition of MAC. Transforming growth factor-beta 1, interleukin-10 and interleukin-6 have all been shown to counteract the immunoactivating cytokines and MAC survival may be due to induction of these inhibitory cytokines within the macrophage. GM-CSF has been given to patients with disseminated MAC infection. Isolated macrophages from these patients demonstrated increased superoxide anion production and enhanced mycobacteriostatic/cidal activity compared with macrophages isolated from the same patients before GM-CSF treatment. These results suggest that GM-CSF may have potential in the treatment of MAC infection.

Exposure to ethanol up-regulates the expression of Mycobacterium avium complex proteins associated with bacterial virulence

Mycobacterium avium complex (MAC) organisms are the most common bacterial cause of disseminated infection in patients with AIDS. MAC, facultative intracellular bacteria, invade and multiply within macrophages. Treatment of MAC-infected macrophages with ethanol (10-100 micrograms/dL) is associated with increased intracellular multiplication of MAC. To investigate whether this enhanced growth is due to a stress-related response induced by nonlethal concentrations of ethanol, strain 101 (serovar 1) was exposed to ethanol, and the regulation of the expression of proteins was examined. Exposure of MAC to ethanol (range, 10-100 micrograms/dL) was associated with up-regulation of the expression of a number of bacterial proteins, some of which (65 and 33 kDa) interfered with macrophage functions, such as production of superoxide anion and killing of Staphylococcus aureus. Thus, exposure of MAC to small concentrations of ethanol may induce a stress-related response with consequent increase in the synthesis of proteins possibly associated with its ability to survive within macrophages.

Comparison of the virulence for mice of Mycobacterium avium and Mycobacterium intracellulare identified by DNA probe test

The virulence of various serovars of Mycobacterium avium and M. intracellulare identified by DNA probe test was compared with each other. We found species- and serovar-dependencies of M. avium complex (MAC) virulence to mice in terms of mortality, incidence of lung lesions and bacterial load in the visceral organs, as follows. First, human- or environment-derived M. intracellulare was more virulent for mice, as compared to M. avium isolated from patients or environmental sources. Second, the virulence of MAC isolates belonging to serovars 1, 8, 9 (M. avium), 14 and 16 (M. intracellulare) is in the order of serovars 16 > 14 > 8 > 1 > 9. These aspects were different from those for MAC virulence to human and bird, swine and cattle.

Colonial morphotype as a determinant of cytokine expression by human monocytes infected with Mycobacterium avium

Mycobacterium avium is an intracellular pathogen that causes disseminated infection in patients with AIDS. Colonial morphotype (smooth-transparent (SmT) vs smooth-domed (SmD)) is a key determinant of virulence in mice and the capacity for replication in human monocytes. Some cytokines (IL-1 and IL-6) promote, whereas others (IFN-gamma and TNF) inhibit intracellular M. avium growth. The specific factors that determine virulence of M. avium, however, are not clear. In this study, we examined cytokine expression by human monocytes stimulated with isogeneic cloned isolates of M. avium. Monocytes were prepared from healthy donors and cultured with or without isogeneic M. avium for up to 7 days. Cytokine levels (IL-1, IL-6, and TNF-alpha) in monocyte supernatants and cell lysates were measured by immunoassay using an ELISA. The expression of cytokine mRNA by monocytes infected with M. avium also was determined by extracting total RNA and subjecting it to Northern blot analysis. Optimal cytokine release occurred at 24 h. SmD induced higher levels of the following cytokines in supernatants than SmT: IL-1 alpha (140 +/- 32 (mean +/- SE) vs 47 +/- 16 pg/ml, p < 0.02), IL-1 beta (4.0 +/- 0.9 vs 1.7 +/- 0.5 ng/ml, p < 0.01), and TNF-alpha (2725 +/- 546 vs 1464 +/- 409 pg/ml, p < 0.01). IL-6 production was comparable for both strains. SmD and SmT isolates induced comparable levels of steady state mRNA for IL-1 beta, TNF, and IL-6. Pulse-chase analysis indicated that differences in cytokine expression between SmT and SmD occurred in monocyte lysates at the earliest time point (immediately after pulse-labeling). The dissociation of the expression of specific mRNA from production of IL-1 and TNF suggests that translational capacity for the expression of certain cytokines was reduced by the more virulent SmT. Differential induction of cytokine may be a factor in the pathogenicity of M. avium strains isolated from patients with AIDS.

Mycobacterium avium-M. intracellulare binds to the integrin receptor alpha v beta 3 on human monocytes and monocyte-derived macrophages

Mycobacterium avium-M. intracellulare is an intracellular pathogen responsible for the highest incidence of disseminated bacterial infection in patients with AIDS. Treatment of the infection is difficult and has been of limited efficacy. Attachment of the organism to macrophages is a critical early step in the establishment of the disease. In the present study, we isolated and identified a receptor that mediates attachment of M. avium-M. intracellulare to human peripheral blood monocytes and monocyte-derived macrophages. On Western blotting, (immunoblotting), the receptor was found to cross-react with antibodies against a human vitronectin receptor (alpha v beta 3). The receptor could be purified from monocyte extracts by using monoclonal antibodies (MAbs) against the alpha v subunit of vitronectin receptor coupled to CNBr-Sepharose 4B, as well as with the adhesive tripeptide sequence arginine-glycine-aspartic acid (RGD) coupled to CNBr-Sepharose 4B. Surface-bound MAbs directed against alpha v beta 3 were found to inhibit the attachment of M. avium-M. intracellulare to monocyte-derived macrophages in an in vitro inhibition assay, while MAbs directed against CD14, CD18, alpha 2 beta 1 and platelet glycoprotein gpIIb/IIIa receptors did not inhibit this attachment. These observations suggest that alpha v beta 3 on the surface of human monocytes and monocyte-derived macrophages may function as a receptor for M. avium-M. intracellulare. Identification of a receptor for M. avium-M. intracellulare on macrophages may offer new approaches to the prevention and control of M. avium-M. intracellulare infection at the cellular level.

Mycobacteria in Crohn's disease: DNA probes identify the wood pigeon strain of Mycobacterium avium and Mycobacterium paratuberculosis from human tissue

Mycobacterium paratuberculosis is known to cause Johne's disease, a granulomatous ileitis in ruminants, and may be involved in some cases of Crohn's disease. Like M. paratuberculosis, the wood pigeon strain of Mycobacterium avium may also show mycobactin dependence on primary isolation that is attenuated on further subculturing. A wood pigeon strain, M. avium restriction fragment length polymorphism (RFLP) type A/I, is also capable of causing granulomatous ileitis in experimental animal models but is not known to cause disease in humans. M. avium RFLP type A is associated with disease in immunocompromised hosts. Three DNA probes, pMB22 and the two subclones pMB22/S4 and pMB/S12, were found to be capable of distinguishing among M. paratuberculosis, M. avium type A, and M. avium type A/I (wood pigeon strain) on the basis of RFLPs. These DNA probes were used to identify two mycobacterial isolates (M. paratuberculosis and M. avium type A/I, wood pigeon strain) derived from the intestinal tissues of two patients with Crohn's disease. In addition, the wood pigeon strain of M. avium was identified from a patient with ulcerative colitis, and M. avium RFLP type A was identified from a patient with colonic carcinoma. This is the first time that M. avium A/I (wood pigeon strain) is known to have been isolated from human tissue. There are too few isolates to speculate about the etiological significance of mycobacteria and inflammatory bowel disease, but it is reasonable to conjecture that M. paratuberculosis may be responsible for some cases of Crohn's disease and that the wood pigeon strain of M. avium may also be an inflammatory bowel disease pathogen in humans.

Comparison of the abilities of Mycobacterium avium and Mycobacterium intracellulare to infect and multiply in cultured human macrophages from normal and human immunodeficiency virus-infected subjects

Patients with AIDS commonly develop disseminated infections with Mycobacterium avium (MA) but not its close relative, M. intracellulare (MI). In non-AIDS patients who have these infections, the two species are about equally distributed. The higher incidence of infection with MA than with MI in AIDS patients might be due to the selective susceptibility of these patients to MA. This possibility was tested by comparing the abilities of MA and MI to infect and replicate in cultured macrophages from normal subjects and from patients with AIDS-related complex or AIDS. The macrophages were cultured in medium supplemented with 1 or 5% normal or patient sera or with 1% defined serum substitute. Replication of MA (serovar 4) or MI (serovars 16 and 17) in the macrophages was measured by CFU counts made from lysed samples of the macrophages taken at 0,4, and 7 days after macrophage infection. MA and MI in infected normal macrophages which were cultured in normal serum replicated in these macrophages at similar rates. MA but not MI multiplied abnormally rapidly in patient macrophages cultured in either normal serum or patient serum. The accelerated growth of MA in patient macrophages was macrophage dependent, because patient sera did not change the rate of MA replication in culture medium lacking macrophages. However, patient sera did increase the permissiveness of normal macrophages to MA but not MI. These results suggest that a selective increased susceptibility to MA compared with a retained normal resistance to MI in human immunodeficiency virus-infected patients as they progress from AIDS-related complex to AIDS accounts for the higher prevalence of MA than MI infection in AIDS patients. The results also indicate that the mechanisms of native resistance in human macrophages to MA and MI are different.

Macrophages, mycobacteria and HIV: the role of cytokines in determining mycobacterial virulence and regulating viral replication

The marriage of two scourges, one old (mycobacterial disease) and one new (HIV), has presented an enormous challenge to the medical and public health communities, and has stirred renewed interest in mechanisms for immune control of mycobacterial infection. Virulence of both M. avium and M. tuberculosis appears to be inversely related to the capacity of the microorganisms to induce production of protective cytokines in infected hosts. TNF alpha and IFN gamma are central to this process, and mycobacterial polysaccharides may be their main determinant. Despite these similarities, M. tuberculosis and M. avium cause illnesses at the polar extremes of HIV disease. Tuberculosis, occurring early in the course of HIV disease, may promote HIV replication in otherwise latently infected cells via induction of cytokines. As such, the potential exists for accelerated progression to AIDS due to the mutual synergy of these pathogens.

Differential release of interleukin (IL)-1 alpha, IL-1 beta, and IL-6 from normal human monocytes stimulated with a virulent and an avirulent isogenic variant of Mycobacterium avium-intracellulare complex

Members of the Mycobacterium avium-intracellulare complex (MAC) can exist in a transparent or opaque colonial morphology when cultured on synthetic medium. An opaque variant was developed from a transparent strain of a clinical MAC isolate. Comparison of the two variants showed a greater ability of the transparent colonial variant to infect normal human monocytes as measured by growth in monocyte-bacteria cocultures. Further analyses indicated diminished ability of the transparent variant to induce extracellular secretion of interleukin (IL)-1 and IL-6, as well as membrane-associated IL-1 when compared with the opaque isotype. At the molecular level, induction of specific IL-1 alpha, IL-1 beta, and IL-6 mRNAs was consistent with the protein results. These results suggest that the virulent transparent MAC, as opposed to the avirulent opaque type, may escape host defenses by failing to induce IL-1 and IL-6, key factors in the initiation of a normal immune response.

[The comparison of drug susceptibility of antituberculous agents against colonizing M. intracellulare and infectious M. intracellulare]

The susceptibility of antituberculous agents against colonized M. intracellulare which were isolated from patients with pulmonary disease and infectious M. intracellulare (pathogens) isolated from atypical mycobacterial culture was investigated. Aminoglycosides were more potent against colonized organisms than against pathogens. Isoniazid, ethambutol and rifampicin showed less potent antimicrobial activity against both colonized organism and pathogens as compared to aminoglycosides. On the contrary susceptibility of cycloserine against colonized organisms was as potent as against pathogens.

Genotypic identification of pathogenic Mycobacterium species by using a nonradioactive oligonucleotide probe

Commercial DNA hybridization assays (Syngene, Inc., San Diego, Calif.) utilizing alkaline phosphatase-labeled oligonucleotide probes for the identification of Mycobacterium tuberculosis complex and M. avium complex (MAC) were evaluated with 261 isolates of mycobacteria. On the basis of biochemical criteria, the test for MAC was 98% specific and more sensitive (95 of 99, 95%) than Gen-Probe (88 of 99, 89% sensitivity); the major difference in sensitivity noted between the two systems was related to the hybridization of seven MAC strains to the SNAP X probe. The M. tuberculosis complex probe correctly identified all 62 isolates of M. tuberculosis and all 11 isolates of M. bovis, for a sensitivity of 100%. There were two discrepant reactions with mycobacteria other than M. tuberculosis complex isolates.

Microtiter plate assay for selecting "macrophage virulent" strains of Mycobacterium avium intracellulare mycobacteria in mouse pulmonary alveolar macrophages

Currently used macrophage-mycobacterial in vitro infection models require substantial numbers of macrophages. We developed a miniaturized version of such a model, using microtiter plates, which is comparable to standardly published methods, is reproducible, and requires fewer macrophages. In addition to its ease of handling and its economy in time, number of animals, and supplies, this method is preferable when limited numbers of macrophages are available. We have used this assay as a means of selecting human derived isolates from patients with M. avium intracellulare pulmonary disease for their ability to infect and multiply in cultured mouse pulmonary alveolar macrophages.

Strain- and donor-related differences in the interaction of Mycobacterium avium with human monocytes and its modulation by interferon-gamma

Mycobacterium avium is a cause of disseminated infection in AIDS patients. The pathogenicity of M. avium for human monocytes was examined in an in vitro model. Peripheral blood monocytes obtained from 13 healthy donors were precultured for 2 days before infection. Monocytes were infected with six AIDS-associated and three non-AIDS-associated strains and four strains of M. avium selected on the basis of colonial morphology. Uptake of M. avium detected by counting intracellular acid-fast bacilli differed according to colonial morphology: Bacteria with round and opaque colony forms were phagocytosed more readily than those with flat colonies. Virulence as defined by intracellular growth was also partly associated with colonial morphology. Some but not all bacilli with flat colony forms multiplied in human monocytes; strains of the round opaque colonial form did not. The effects of recombinant human interferon-gamma on M. avium infection also were examined. Pretreatment of monocytes suppressed phagocytosis. After infection, coculturing usually augmented mycobacterial growth inhibition by human monocytes, but these effects were variable from strain to strain. Overall, interferon-gamma produced a small but statistically significant inhibition of intracellular growth in three of four strains tested.

The beige mouse model for Mycobacterium avium complex (MAC) disease: optimal conditions for the host and parasite

We extended our earlier studies to establish the beige (C57B1/6/bgJ/bgJ) mouse model for experimental acute infections with Mycobacterium avium complex (MAC). Optimal conditions of the host and the parasites have been determined. Mice bred at our center showed similar responses to those obtained from Jackson Laboratories, the original supplier. Both male and female mice showed similar responses, but older mice in both sexes showed less susceptibility than younger mice. Strain 101 of MAC showed remarkable consistency in its pathogenicity to beige mice, as evidenced by the distribution of colony forming unit (CFU) counts at various time points after intravenous challenge, in several experiments. CFU counts showed an association with the dose of challenge, and histopathological observations.

Virulence of Mycobacterium avium complex strains from acquired immune deficiency syndrome patients: relationship with characteristics of the parasite and host

The virulence of 24 strains of Mycobacterium avium complex (MAC) isolated from patients with acquired immune deficiency syndrome (AIDS) was assessed using the beige mouse model. Most changes in colony forming unit (cfu) counts in spleen and lungs, and spleen weights occurred between days 1 and 14, with comparatively smaller changes 14-28 days postinfection. The virulence was assessed by a score formulated from the four most useful parameters: mortality, spleen cfu, lung cfu and spleen weights at 28 days. The scores of the 24 strains showed a normal distribution; four strains falling above one standard deviation from the mean were classified as high virulent, those four falling below one standard deviation as low virulent, and the remaining 16 as of intermediate virulence. Virulence was associated with the total number of plasmids and the occurrence of large plasmids (greater than 100 MDa) in the MAC strains. There was an inverse correlation between virulence and the organism's capacity to trigger the release of oxygen metabolites from peritoneal macrophages. Macrophages from mice infected with the MAC strains of different degrees of virulence released superoxide anion (O2-) with a peak at two weeks, the peak levels bearing an inverse correlation to virulence. No association was seen between virulence and source of specimens, biochemical characteristics, drug susceptibility, serotypes or phage types.

Mycobacterium avium complex and other nontuberculous mycobacteria in patients with HIV infection

Nontuberculous mycobacteria (NTM) have been frequently identified as opportunistic pathogens in individuals with advanced human immunodeficiency virus (HIV) infection. The majority of these infections have been caused by members of the Mycobacterium avium-intracellulare complex (MAC). Disseminated MAC infection has generally been diagnosed late in the course of HIV infection, and it is often associated with persistent nonspecific symptoms of fever, generalized weakness, and weight loss. Abdominal pain and/or diarrhea with malabsorption may also occur in some patients. Despite frequent isolation of MAC organisms from respiratory secretions in these patients, significant pulmonary involvement has not been seen commonly with disseminated MAC infection. While MAC can be isolated from a variety of clinical specimens in infected individuals, culturing of blood is the single most useful diagnostic procedure to evaluate for MAC infection. The prognosis for disseminated MAC infection in HIV-infected patients has been poor, with a reported median survival of 7.4 months after diagnosis. The overall contribution of MAC infection to mortality in these patients has not been clearly delineated. Treatment of MAC infection in HIV-infected individuals using a variety of drug regimens has not been effective in clearing mycobacteremia or improving overall survival in the majority of patients. However, initiation of drug therapy for MAC may decrease the severity of disease symptoms in some patients. Several NTM other than MAC have also been reported as causing infection in HIV-infected patients. Many of these organisms are ubiquitous in the environment and are frequent colonizers of biologic specimens. Although many NTM are regarded as relatively avirulent, these organisms need to be recognized as potentially important pathogens in HIV-infected patients with significant immunosuppression.

[Macrophage respiratory burst-triggering activity of transparent and opaque colonial variants of Mycobacterium avium complex]

The two types of colonial variants of Mycobacterium avium complex, SmT (smooth, transparent, irregular) and SmD (smooth, opaque, dome-shaped) variants, were examined for their triggering activity for macrophage (M phi) respiratory burst, based on chemiluminescence (CL). SmD variants elicited an intense CL from zymosan A-induced M phi s in a dose-dependent manner, although SmT variants induced much lower M phi CL. The M phi s could steadily phagocytose SmT variants, although the phagocytizing rate was considerably lower compared to the case of SmD variants. Treatments of SmD variants with Tween 80, pronase and some endoglycosidases such as alpha-amylase, cellulase, dextranase and pectinase, heating (100 degrees C, 15 min), and delipidation by CHCl3-methanol extraction resulted in a marked reduction in the M phi CL-triggering activity of the SmD variants. Thus, the M phi CL-triggering ligand(s) seems to possess glycolipoprotein-like moieties. Tween 80-treatment of SmT variants, which is known to deprive the polysaccharide outer layer specific to the colonial variants, failed to recover the M phi CL-triggering activity of SmT variants. Therefore, the remarkably reduced M phi CL-triggering ability of the SmT variants may be caused by the extremely lowered expression of the M phi CL-triggering ligands rather than by masking of the CL-triggering ligands by SmT-specific outer layer.

The hamster model of chronic Mycobacterium avium complex infection

Male golden Syrian hamsters were evaluated as a model for the pathogenesis of human infection with Mycobacterium avium complex. Intratracheal inoculation produced a chronic, nonfatal, pulmonary and disseminated infection (overall rate, 86%). The frequency of infection in hamsters that received 5 x 10(8) versus 1 x 10(8) colony forming units (cfu) was not significantly different (87% and 92%, respectively), but 1 x 10(7) cfu produced infection in only 78% of inoculated animals (P = .034). The percentage of animals developing pulmonary infection with M. avium complex did not differ between inoculum groups (77%-80%). Disseminated infection occurred significantly less frequently in the 1 x 10(7) group (46%) compared with the 5 x 10(8) (79%) and 1 x 10(8) (68%) groups (P = .001 and .056, respectively). After seven weeks, partial clearance of M. avium complex from the lungs coincided with an increased number of animals with splenic involvement. The hamster may be a useful model for human infection with M. avium complex.