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Biomedical subjects

N Rastogi

Publications and source records attributed to N Rastogi.

At least 127 records · Page 7Linked to original sources
PubMed1989

Methionine as methyl-group donor in the synthesis of Mycobacterium avium envelope lipids, and its inhibition by DL-ethionine, D-norleucine and DL-norleucine.

The radioactivity from 3H-methyl methionine was rapidly incorporated into the surface lipids of Mycobacterium avium. The transmethylation reaction was efficiently inhibited by DL-ethionine, D-norleucine and DL-norleucine. The structure of the outerlayer of the M. avium envelope was profoundly altered in the bacteria treated with DL-norleucine.

Cell Wall↗
PubMed1989

Isoenzymes as tools to discriminate various subdivisions in the Mycobacterium fortuitum complex.

Methods for the characterization of catalase, peroxidase, beta-glucosidase, esterase, and beta-lactamase mycobacterial isoenzymes were described. These methods were applied to examine strains of the M. fortuitum complex. M. fortuitum, M. peregrinum, M. chelonae- M. abscessus and an unnamed species had distinct isoenzyme profiles. M. chelonae and M. abscessus could not be satisfactorily differentiated using the described methods.

Catalase↗
PubMed1989

Isoenzymes profiles in slowly-growing and difficult-to-grow mycobacteria.

The cell-free extracts of 13 slowly-growing mycobacteria were run on polyacrilamide gels (Page) and the various protein bands obtained were tested for peroxidase and catalase enzyme activities. The results obtained were compared to those obtained with M. fortuitum and M. chelonae. Based only on a limited numbers of strains employed, it is suggested that these isoenzyme patterns may permit a better separation of "Wood-pigeon" mycobacteria from both M. avium and M. paratuberculosis and also give distinct profiles for other species used. These results further suggest the potential of isoenzymes as taxonomic markers.

Catalase↗
PubMed1988

Mechanisms of pathogenicity in mycobacteria.

The purpose of this article is to review current knowledge about the mechanisms of pathogenicity of mycobacteria. The following aspects of the problem are discussed: chemically-defined compounds implicated in the mechanisms of pathogenicity; location in the cell wall of these compounds and their biological activities; mechanisms of intracellular survival of pathogenic mycobacteria as compared to intracellular killing of non-pathogenic mycobacteria; and pathogenesis of mycobacterial infection. The future prospects in the elucidation of the mechanisms of pathogenicity and their possible application for a better control of mycobacterial diseases are briefly discussed.

Animals↗
PubMed1988

Further studies on colistin (polymyxin E)-induced cell leakage in mycobacteria: Mg++ efflux in Mycobacterium avium and its effects on drug-susceptibility.

Action of colistin (polymyxin E) was investigated on the opportunistic pathogenic species Mycobacterium avium ATCC 15769 (resistant strain, MIC greater than 100 micrograms/ml). Mycobacterium intracellulare ATCC 13950: a colistin-susceptible strain (MIC 25 micrograms/ml), was used as a parallel control for Mg++ efflux experiments. After the addition of 100 micrograms/ml of colistin to bacteria suspended in a buffer, both loss of viability and Mg++ efflux were followed for one week. Although there was an initial Mg++ efflux in both strains, it soon attained a plateau in case of the resistant strain without any loss of viability until 48 h, whereas in case of the susceptible strain, Mg++ efflux was about 3 times higher than former, a plateau was attained only 24 h after the drug addition, and the loss of viability started only 6 h after the drug addition. Consequently, the loss of viability of M. avium with later incubation times (6 days) was not due to the action of colistin on the cytoplasmic Mg++ efflux solely, but some additional effect was implicated. The drug-susceptibility of extracellularly-growing and intracellularly-growing (in the J-774 macrophage cell line) M. avium to the antibiotics tested could not be potentiated when they were used in combination with 5 micrograms/ml of colistin (maximal obtainable serum level in man) or the polymyxin B nonapeptide (PMBN), nor in the case of bacteria pretreated with these molecules.

Amoxicillin↗
PubMed1988

Antibacterial action of amphipathic derivatives of isoniazid against the Mycobacterium avium complex.

The antibacterial action of amphipathic derivatives of isoniazid (INH) as compared to the parent hydrophilic molecule was determined against the bacteria of the Mycobacterium avium complex (MAC) using a 7H11 agar-dilution method. The results obtained showed a higher activity of 1-isonicotinyl-2-palmitoyl hydrazine and 1-isonicotinyl-2-(12 hydroxy dodecanoyl) hydrazine as compared to INH. However, when one mannose residue was terminally attached to the fatty acid chain of the latter, it lost its anti-MAC activity. 1-isonicotinyl-2-D-galacturonic acid hydrazone (but not hydrazine) also showed increased activity against MAC. Although pristinamycin was shown to bind to M. avium surface lipids, the INH-pristinamycin derivative was not more active than INH alone. These findings are discussed in respect to a proposed mechanism of diffusion across a lipid barrier.

Anti-Bacterial Agents↗
PubMed1987

Studies on clofazimine-resistance in mycobacteria: is the inability to isolate drug-resistance mutants related to its mode of action?

This study showed that clofazimine was not radiomimetic, it was not a mutagenic compound, it was not an inducer of prophage-lambda, and it did not eliminate plasmids from appropriate host bacteria. The drug caused an effective inhibition of the growth of Mycobacterium aurum, and also inhibited the growth cycle of the mycobacteriophage D29. Cross-resistance between clofazimine, streptomycin and rifampicin could not be demonstrated. Drug-resistance mutants towards clofazimine could not be isolated, and it was found that the existing clofazimine-resistant strains of Mycobacterium tuberculosis were rather susceptible organisms requiring clofazimine in their growth medium to maintain their drug-resistance. Ultrastructural studies showed that clofazimine did not act by cell wall lysis, nor did it act on bacterial ribosomes. Higher concentrations of the drug resulted in bacterial plasmolysis. These findings are discussed in the light of its known properties and proposed mode of action.

Clofazimine↗
PubMed1987

Structure of the cell envelope of Mycobacterium avium.

In this report the cell wall of Mycobacterium avium is shown as a triple-layered structure where the outermost layer was stained by the ruthenium red staining for polysaccharides. The outermost layer hindered the diffusion of chemotherapeutic agents across the wall thus causing multiple drug-resistance by exclusion. The concerted electron microscopy and chemical analysis of chloroform-methanol and Triton X-100 extracts indicated that the outer layer was made of diverse amphiphil glycolipids (mycosides C, glycolipids, peptidolipids, phospholipids) that formed a matrix in which proteins were embedded. The examination of a spontaneous rough mutant indicated that mutations blocking the synthesis of one or several of the amphiphils must leave unsubstituted mycolic acid residues, thus causing surface hydrophobicity and roughness. Judging from our data, a model describing the overall cell envelope of M. avium was proposed. From the comparative analysis of M. avium, its spontaneous rough mutant, and its spheroplasts, some of the functions of the outermost layer were disclosed.

Antigens, Bacterial↗
PubMed1987

Colistin (polymyxin E)--induced cell leakage in Mycobacterium aurum.

Addition of 100 micrograms/ml of colistin (polymyxin E) to an actively-growing culture of Mycobacterium aurum caused apparent loss of viability starting after 20 min of drug addition, whereas significant Mg++ efflux was apparent within 5 min of drug addition. Therefore, Mg++ efflux preceded cell death by at least 15 min. These data confirmed earlier reports showing that colistin interacted with the cytoplasmic membrane of mycobacteria.

Cell Membrane↗
PubMed1987

Mycobacterium leprae surface components intervene in the early phagosome-lysosome fusion inhibition event.

Bone marrow-derived cultured macrophages were infected with Mycobacterium leprae. The bacteria were either used as freshly isolated organisms or incubated with M. leprae antiserum (1:5) for 30 min prior to phagocytosis. Immediately after inoculation (1 to 4 h) and at 1 to 8 days later, macrophages were stained for acid phosphatase activity to assess fusions between phagosomes and lysosomes. Inhibition of fusions was essentially apparent as an early event, which was partially reversed by antiserum treatment of the bacteria, suggesting a role for M. leprae immunogenic surface components in this early phenomenon. Later incubation times (1 to 8 days) did not show any considerable difference between antiserum-treated and nontreated bacteria. The formation of an electron-transparent zone around phagocytized bacteria and its role in phagosome-lysosome fusion was investigated, and a direct relationship could not be established.

Acid Phosphatase↗
PubMed1986

Action of colistin (polymyxin E) on the lytic cycle of the mycobacteriophage D29 in Mycobacterium tuberculosis.

The antibiotic colistin (polymyxin E) inhibited the lytic cycle of the mycobacteriophage D29 in the tubercle bacilli, but not the D29 adsorption. The protein and nucleic acid synthesis in D29-infected bacteria were not affected significantly. The inhibitory activity was reversed by washing off the antibiotic, and by addition of Ca++, but not in media made iso-osmotic by addition of NaCl or sucrose. Transmission electron microscopy revealed an asymmetric to symmetric transition in the staining profile of the cytoplasmic membrane. Though no mature phage particles were ever observed in colistin-treated, D29-infected tubercle bacilli, loosely arranged aggregates resembling phage proheads were occasionally found. Judging from the above data, it was concluded that colistin inhibited D29 lytic cycle by causing molecular displacements in the inner leaflet of the cytoplasmic membrane, and consequently, the binding sites for D29 structural proteins were not available.

Adsorption↗
PubMed1986

Evidence for inhibition of fusion of lysosomal and prelysosomal compartments with phagosomes in macrophages infected with pathogenic Mycobacterium avium.

Bone marrow-derived cultured macrophages were infected with the pathogenic organism Mycobacterium avium. Immediately after infection and at 1 to 28 days later, cells either were stained for acid phosphatase activity or given horseradish peroxidase, which served as a pinocytotic marker. With the former, fusions between phagosomes and lysosomes exclusively were assessed; with the latter, those between phagosomes and both pinosomes and lysosomes were determined. As a control, similar experiments were undertaken by infecting macrophages with gamma ray-killed M. avium and the nonpathogenic live organisms Mycobacterium aurum and Bacillus subtilis. After infection with live M. avium, fusions between phagosomes and acid phosphatase-positive vesicles (lysosomes) were inhibited. The same inhibition was observed whether phagosomes contained damaged or structurally intact (presumed to be live) bacteria, except for the early time points. This inhibition was, however, partial, suggesting that some of the live bacteria are resistant to the hydrolytic enzymes of the phagolysosomal environment. Fusions between horseradish peroxidase-positive vesicles (pinosomes and lysosomes) and phagosomes depended upon the morphological state of the bacteria. Damaged bacteria did not inhibit fusions, whereas with intact bacteria, a partial inhibition which increased with time was observed. The two types of experiment suggest that viable M. avium can impair phagosome-pinosome fusions.

Acid Phosphatase↗
PubMed1985

Antibacterial action of colistin (polymyxin E) against Mycobacterium aurum.

Mycobacterium aurum was susceptible to the antibiotic colistin (polymyxin E),which had an MIC of 5 micrograms/ml and an apparent bactericidal effect at concentrations above 50 micrograms/ml. Treatment of actively growing cells with sublethal concentrations of colistin (15 micrograms/ml) resulted in synchronized cell division once the antibiotic was removed. Under conditions of synchronized cell growth, one cycle of DNA replication lasted 120 min and one cycle of cell division lasted about 180 min. Although the antibiotic treatment during synchronization experiments did not produce apparent changes in the bacterial envelope, it was accompanied by the accumulation of a polysaccharide-like substance in the bacterial cytoplasm which gradually decreased after the removal of antibiotic and by an increase in the number of mesosomes at 3 h after antibiotic removal. This step was closely linked to the doubling time of bacteria. Lethal concentrations of colistin of 50 and 100 micrograms/ml, which caused about 90 and 99% cell death, respectively, produced significant cytoplasmic membrane injuries, patchy appearance of the cell wall outer polysaccharide layer, and little cell lysis. These data indicate that the cytoplasmic membrane is a site of action of colistin and raise a question as to whether an outer bilayer exists in mycobacteria, at least functionally.

Cell Division↗
PubMed1984

Abortive infection of Mycobacterium leprae by the mycobacteriophage D29.

The interactions of mycobacteriophage D29 and Mycobacterium leprae were examined. It was demonstrated that after adsorption D29 injected its DNA in M. leprae. While the synthesis of host proteins and lipids were inhibited in M. tuberculosis and in M. smegmatis during infection by D29, the results were inconclusive in the case of M. leprae because these bacteria did not incorporate the appropriate substrates.

DNA, Bacterial↗
PubMed1983

Spheroplast fusion as a mode of genetic recombination in mycobacteria.

Spheroplasts were prepared from two carotenoid pigment mutants of Mycobacterium aurum named NgR9 and A11, which were obtained by the chemical mutagenesis of the wild type strain A+ with N-methyl-N'-nitro-N-nitrosoguanidine. The carotenoid pigments and the alpha- and beta-mycolic acids were taken as genetic markers and the recombinants were selected on the basis of their colour on Löwenstein-Jensen medium. Spheroplasts of the two mutants were mixed in a 1:1 ratio and were treated with 40% (w/v) polyethylene glycol 6000 for 5 min at 37 degrees C. The frequency of NgR9 X A11 recombination in optimal conditions was about 2.5 X 10(-3). The recombinants selected on the basis of their carotenoid pigment profile were also tested for their alpha- and beta-mycolic acids as a second genetic marker. The results were further confirmed by electron microscopy. The optimal conditions for spheroplast fusion as a mode of genetic recombination in M. aurum are described.

Carotenoids↗
PubMed1981

Ultrastructural and chemical studies on wall-deficient forms, spheroplasts and membrane vesicles from Mycobacterium aurum.

Wall-deficient forms of Mycobacterium aurum were prepared by agitating the cells during exponential growth with D-cycloserine, glycine, lysozyme, EDTA and LiCl for approximately the time of three cell divisions (18 h). Wall-deficient forms were then converted to spheroplasts by gentle stirring with lysozyme and EDTA in a Tris/HCl buffer containing sucrose until all the cells appeared spherical by phase contrast microscopy. Subsequent lysis by nucleases followed by osmotic shock produced membrane vesicles. Ultrastructural and chemical properties of the spheroplasts and membrane vesicles are described. The spheroplasts were susceptible to lysis by 0.25% (w/v) sodium dodecyl sulphate and were permeable to certain enzyme substrates.

Anti-Bacterial Agents↗