Mycobacterium Avium Complex Bacteria Research Articles

Mycobacterium avium complex bacteria remain viable in sputum during storage and refrigeration

Diagnostic mycobacteriology often involves shipping of samples to centralized laboratories. Using two quantitative culture techniques, we show that 7 days storage of sputum samples at room temperature or 4 °C does not affect the number of viable Mycobacterium avium complex bacteria. Storage at room temperature increases the chance of contamination.

Nontuberculous Mycobacteria in Respiratory Tract Infections, Eastern Asia

Abstract To characterize the distribution of nontuberculous mycobacteria (NTM) species isolated from pulmonary samples from persons in Asia and their association with pulmonary infections, we reviewed the literature. Mycobacterium avium complex bacteria were most frequently isolated (13%–81%) and were the most common cause of pulmonary NTM disease (43%–81%). Also pathogenic were rapidly growing mycobacteria (M. chelonae, M. fortuitum, M. abscessus). Among all NTM isolated from pulmonary samples, 31% (582/1,744) were considered clinically relevant according to American Thoracic Society diagnostic criteria. Most patients were male (79%) and had a history of tuberculosis (37%). In Asia, high prevalence of rapidly growing mycobacteria and a history of tuberculosis are distinct characteristics of pulmonary NTM disease. This geographic variation is not well reflected in the American Thoracic Society criteria for NTM infections and could be incorporated in future guidelines.

Nontuberculous Mycobacteria in Respiratory Tract Infections, Eastern Asia

To characterize the distribution of nontuberculous mycobacteria (NTM) species isolated from pulmonary samples from persons in Asia and their association with pulmonary infections, we reviewed the literature. Mycobacterium avium complex bacteria were most frequently isolated (13%–81%) and were the most common cause of pulmonary NTM disease (43%–81%). Also pathogenic were rapidly growing mycobacteria (M. chelonae, M. fortuitum, M. abscessus). Among all NTM isolated from pulmonary samples, 31% (582/1,744) were considered clinically relevant according to American Thoracic Society diagnostic criteria. Most patients were male (79%) and had a history of tuberculosis (37%). In Asia, high prevalence of rapidly growing mycobacteria and a history of tuberculosis are distinct characteristics of pulmonary NTM disease. This geographic variation is not well reflected in the American Thoracic Society criteria for NTM infections and could be incorporated in future guidelines.

Nontuberculous Mycobacteria in Respiratory Tract Infections, Eastern Asia

To characterize the distribution of nontuberculous mycobacteria (NTM) species isolated from pulmonary samples from persons in Asia and their association with pulmonary infections, we reviewed the literature. Mycobacterium avium complex bacteria were most frequently isolated (13%-81%) and were the most common cause of pulmonary NTM disease (43%-81%). Also pathogenic were rapidly growing mycobacteria (M. chelonae, M. fortuitum, M. abscessus). Among all NTM isolated from pulmonary samples, 31% (582/1,744) were considered clinically relevant according to American Thoracic Society diagnostic criteria. Most patients were male (79%) and had a history of tuberculosis (37%). In Asia, high prevalence of rapidly growing mycobacteria and a history of tuberculosis are distinct characteristics of pulmonary NTM disease. This geographic variation is not well reflected in the American Thoracic Society criteria for NTM infections and could be incorporated in future guidelines.

Fever and Pancytopenia in a Patient with AIDS: (Answer on pages 1358–9)

Diagnosis: disseminated infection due to Mycobacterium avium complex (MAC). Cultures of both peripheral blood samples and bone marrow aspirates demonstrated the presence of MAC (figures 1 and 2). MAC comprises 2 species, M. avium and Mycobacterium intracellulare. They are environmental saprophytes that are found ubiquitously in soil, water, and food, and exposure is, therefore, inevitable. The incidence of MAC infection increases when the CD4+ cell count has decreased to <50 cells//*L. Disseminated infection due to MAC is one of the leading causes of pyrexia of unknown origin among HIV-positive patients and is defined as isolation of MAC bacteria by culture from sites other than sputum, stool, or skin samples and the presence of a concurrent illness consistent with the diagnosis [ 1 ] . Biopsy of bone marrow for culture and morphological examination has a high diagnostic yield in this setting. The high mycolic content of the cell wall of Mycobacterium species is responsible for the poor absorption and penetration by aqueous-based staining solution and, thus, their appearance as negatively stained curvilinear structures in the histiocytes. Recognition of the negatively stained inclusions in the histiocytes is important, because wellformed granuloma may not be present in patients with AIDS who have disseminated mycobacterial infection [2]. With the advent of HAART and chemoprophylaxis, the incidence of disseminated MAC infection has decreased substantially [3]. Unfortunately, our patient, who was a resident of mainland China, has been staying in Hong Kong for several months and was not receiving regular medication. The patient's infection was treated with a combination of azithromycin, rifabutin and ethambutol but was complicated by deranged liver function and a deterioration in the patient's general condition, and he died.

Antigenic stimulation in the simian model of HIV infection yields dilated cardiomyopathy through effects of TNFα

To investigate a role for endogenous myocardial cytokine production in the development of HIV-associated cardiomyopathy. Cardiomyopathy is a late-stage sequela of HIV infection. Although pathogenesis of this condition in HIV infection is poorly defined, inflammatory cytokines are recognized for their detrimental effects on myocardial structure and function. HIV infection is characterized by chronic immune activation and inflammatory cytokine dysregulation. As the myocardium itself is a rich potential source of inflammatory cytokines, HIV-mediated cytokine dysregulation may be an important contributor to development of HIV cardiomyopathy. An antigenic stimulation protocol conducted in the simian immunodeficiency virus (SIV) model of HIV infection was used to study the effects of endogenous cytokine production on myocardial structure and function. Twenty-six rhesus monkeys were assigned to treatment groups for a 35-day study. Animals were SIV-infected; SIV-infected and treated with killed Mycobacterium avium complex bacteria (MAC); SIV-infected, MAC-treated, and given the TNFalpha antagonist etanercept; or uninfected and MAC-treated. All animals were subjected to weekly echocardiographic studies. Hearts were collected for further evaluation at euthanasia. SIV-infected, MAC-treated animals developed significant systolic dysfunction [left ventricular ejection fraction (LVEF) decline of 19 +/- 2%] and ventricular chamber dilatation [left ventricular end-diastolic diameter (LVEDD) increase of 26 +/- 6%] not seen in other groups. Concurrent treatment with etanercept prevented development of these changes, implicating a causative role of myocardial TNFalpha. SIV-infected animals develop exaggerated myocardial pathology on stimulation with the ubiquitous environmental agent MAC. These responses are TNFalpha-dependent and may play a significant role in the development of cardiomyopathy in HIV infection.

Activity of subinhibitory concentrations of dapsone alone and in combination with cell-wall inhibitors against Mycobacterium avium complex organisms.

MICs of dapsone (p-p'-diaminodiphenylsulfone) were determined radiometrically for ten strains each of the Mycobacterium avium complex (MAC) and Mycobacterium tuberculosis. MICs ranged from 50 to 250 micrograms/ml for Mycobacterium tuberculosis and from 2 to 100 micrograms/ml for MAC. However, at a concentration as low as 1.5 micrograms/ml dapsone significantly inhibited growth of MAC bacteria when used in combination with other drugs specifically acting at the mycobacterial cell-wall level. The latter drugs were used in subinhibitory concentrations, and included m-fluorophenylalanine (an inhibitor of mycoside-C biosynthesis), ethambutol (an inhibitor of arabinogalactan biosynthesis), and ethionamide (an inhibitor of mycolic acid biosynthesis). Using a radiometric method (Bactec 460-TB), the activity of dapsone was found to be enhanced for 2/10 strains in the presence of m-fluorophenylalanine, for 3/10 strains in the presence of ethambutol and for 5/10 strains in the presence of ethionamide. A satisfactory correlation between the radiometric data and bacterial viable counts was established.

In-vitro evaluation of clarithromycin, temafloxacin, and ethambutol in combination against Mycobacterium avium complex.

The in-vitro activity of clarithromycin, temafloxacin, and ethambutol were assessed by MIC, FIC and intra-macrophage killing determinations alone and in various combinations against ten pigmented and ten non-pigmented strains of Mycobacterium avium complex bacteria. Alone, either clarithromycin or temafloxacin were found to be active against M. avium, but the best results were obtained from combinations of drugs. Clarithromycin and temafloxacin together were found to have an additive effect against two of ten pigmented variants and one of ten non-pigmented variants. Clarithromycin and ethambutol demonstrated a synergistic effect against two pigmented and one non-pigmented strain, and an additive effect against five and three pigmented and non-pigmented strains, respectively. For temafloxacin and ethambutol, additive effects were observed in four and two pigmented and non-pigmented strains, respectively. In cultures of macrophages both clarithromycin and temafloxacin alone reduced the numbers of bacteria growing intracellularly after six days, but the most effective bactericidal combination was clarithromycin, temafloxacin, and ethambutol together.

Mycobacterium avium and Mycobacterium intracellulare chromatotypes defined by curvilinear gradient HPLC of mycolic acids

Seventy-nine strains of Mycobacterium avium complex bacteria (MAC), previously characterized by genetic probe analysis, were assayed using two methods of reverse phase high-performance liquid chromatography (HPLC) that employed curvilinear gradients. Although different in column length and cycle time, the methods produced equivalent results, yielding seven distinct chromatographic patterns (chromatotypes) of M. avium and M. intracellulare based on the ratio of mycolate concentrations in the late vs. the middle of three peak clusters (L:M ratio). The M. avium strains ( n = 36) were assigned to chromototypes I through 4 (L:M ratios < 3), and the M. intracellulare strains ( n = 24) to chromototypes 5 through 7 (L:M ratios > 4). Of 18 Mycobacterium ‘X’ strains, seven resembled M. avium, seven others resembled M. intracellular, and four were intermediate between M. avium and M. intracellulare.

Extracellular and intracellular activities of clarithromycin used alone and in association with ethambutol and rifampin against Mycobacterium avium complex

Mycobacterium avium complex bacteria are opportunistic human pathogens, and their chemotherapy remains a challenge since these organisms are resistant to a majority of routine antituberculous drugs. Recently, a wide range of new macrolide antibiotics has been developed, among which the drug clarithromycin appears to have a selective action against M. avium bacteria. In the present study, we have investigated the action of clarithromycin alone (MIC and MBC determinations) and in association with the routine antimycobacterial drugs ethambutol and rifampin at sublethal concentrations (1 micrograms/ml; below concentrations obtainable in human serum) against M. avium. Our viable count data showed that clarithromycin was bactericidal against all 10 strains of M. avium studied and that its activity was enhanced by ethambutol (in 8 of 9 strains) and rifampin (in 3 of 9 strains). The use of all three drugs in association resulted in higher bactericidal effects than found with any of the drugs used alone or in two-drug combinations in seven of nine strains. The bactericidal effects of various drugs used alone and in combination at concentrations obtainable in human serum were investigated against the type strain ATCC 15769 by using 7H9 broth and BACTEC radiometry (extracellular action) and a J-774 macrophage cell line (intracellular action). A good agreement between the extracellular and intracellular activities was found. Electron microscopy using a ruthenium red cytochemical staining of the bacteria showed that clarithromycin disorganized the outer wall layer and the cytoplasmic membrane in the mycobacterial cell envelope and resulted in formation of large vacuoles inside the cytoplasm, with solubilization of ribosomal structures and consequent plasmolysis. Its association with ethambutol and rifampin resulted in more drastic alterations in the bacterial morphology than were seen with any of the drugs used alone, leading to the removal of the bacterial outer layer, homogenization of cytoplasm, complete cell lysis, and formation of ghosts.

Enhancement of drug susceptibility of Mycobacterium avium by inhibitors of cell envelope synthesis

Treatment of infections caused by Mycobacterium avium complex bacteria still remains a challenge since these organisms are resistant to a majority of antituberculous drugs. M. avium is very often linked with acquired immune deficiency syndrome-associated opportunistic infections. We earlier suggested that one of the strategies for circumventing multiple-drug resistance might be the enhancement of M. avium drug susceptibility by inhibiting the synthesis of the outermost layer of its envelope, which appears to act as an exclusionary barrier for drugs. In this investigation, we have examined this strategy by simultaneously using drugs and the following inhibitors of the M. avium cell envelope: m-fluoro-phenylalanine (an inhibitor of mycoside-C biosynthesis), DL-norleucine (an inhibitor of transmethylation reactions), ethambutol (an inhibitor of arabinogalactan synthesis), EDTA (a divalent-ion chelator), and colistin (an inducer of membrane flux of divalent cations). All the drugs were used in concentrations which were low enough for a possible medical application to be foreseen. This approach, tested on seven strains of the M. avium complex, showed that both m-fluoro-phenylalanine and ethambutol were interesting candidates because they caused significant enhancement of M. avium drug susceptibility.

Comparison of Six Methods for Isolating Mycobacteria from Swine Lymph Nodes

Six laboratory methods were compared for isolating acid-fast bacteria. Tuberculous lymph nodes from each of 48 swine as identified by federal meat inspectors were processed by each of the methods. Treated tissue suspensions were inoculated onto each of eight media which were observed at 7-day intervals for 9 weeks. There were no statistically significant differences between the number of Mycobacterium avium complex bacteria isolated by each of the six methods. Rapid tissue preparation methods involving treatment with 2% sodium hydroxide or treatment with 0.2% zephiran required only one-third to one-fourth the processing time as a standard method. There were small differences in the amount of contamination among the six methods, but no detectable differences in the time of first appearance of M. avium complex colonies.