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Biomedical subjects

H L David

Publications and source records attributed to H L David.

At least 91 records · Page 5Linked to original sources
PubMed1978

Differentiation of mycobacteria by "in vivo" and "in vitro" delayed hypersensitivity reactions.

Guinea pigs were sensitized with heat killed M. tuberculosis, M. kansasii, M. scrofulaceum, and M. avium-intracellulare. Purified Protein Derivatives (PPDs) prepared from each of these organisms were tested for delayed type hypersensitivity by lymphocyte transformation, macrophage migration, and mantoux type skin sensitivity tests. The homologous reactions were consistently more intense than heterologous reactions in all three procedures. The skin test procedure was more sensitive than either in vitro method. Positive skin test reactions were elicited with 2 times and 50 times less antigen than, respectively, the lymphocyte transformation and the macrophage migration tests.

Animals↗
PubMed1977

Thermal and ultraviolet light inactivation of Mycobacterium africanum.

Mycobacterium africanum Yaoundé and Rwanda were more heat-resistant than the tubercle bacilli. The ultraviolet susceptibilities of M. africanum strains were within the range usually found in the mycobacteria (e-1 doses), however marked differences were found in the intersept numbers of the Yaounde and the Dakar types.

Africa, Central↗
PubMed1977

beta-Glucosidase activity in mycobacteria.

A procedure to test beta-glucosidase was developed for identification of the mycobacteria. One hundred and thirty-three strains representing 17 species were assayed in a buffered system containing whole cells and the substrate p-nitrophenyl-beta-D-glucoside. Qualitative differences between species indicated that the test was useful in discriminating among the mycobacteria.

Cell-Free System↗
PubMed1976

Effect of temperature on the rate of the transparent to opaque colony type transition in Mycobacterium avium.

The results of drug susceptibility tests were found to be affected by changes that occur spontaneously in populations of Mycobacterium avium maintained in the laboratory. Because the transparent colony type variant was resistant to antituberculosis chemotherapeutic agents and the opaque colony type variant was usually susceptible to these agents, the transition of transparent to opaque colony type was investigated. The rate of the transition was found to be temperature dependent and, in agreement with a previous report, was found to be about 10(-4) to 10(-5) per generation at 37 C. Reversion was found to occur at a rate of 10(-6) to 10(-7) at 37 C. The mutation rate from susceptibility to resistance to rifampin, kanamycin, and erythromycin was about 10(-8) to 10(-9) mutations per bacterium per generation. Judged from our data, the high rate of the transparent to opaque variation was not caused either by mutator effects or by the occurrence of extrachromosomal genes in these bacteria, but could have been due to selective mechanisms still incompletely understood.

Clone Cells↗
PubMed1976

Differential identification of Mycobaterium szulgai and other scotochromogenic mycobateria.

Strains of scotochromogenic mycobacteria were studied by using numerical taxonomy methods in an attempt to more clearly define Mycobacterium szulgai and to find tests useful in identifying the species. In this study all strains of M. szulgai were strong reducers of nitrate, were slow in hydrolyzing Tween 80, and gave a high semiquantitative catalase reaction. Results obtained indicate that the use of increased pigmentation after 1 h of light exposure at 25 C and that the use of arylsulfatase activity are of questionable diagnostic value in separating the species from other scotochrompgenic mycobacteria.

Arylsulfatases↗
PubMed1976

Temperature relationships in Mycobacterium kansasii: correlation between heat inactivation of protein synthesis and thermal death.

The temperature relationships of Mycobacterium kansasii were investigated. The optimal temperature of growth of these bacteria was between 37 and 38 degrees C, and their thermal death point was about 70 degrees. The temperature characteristic of growth of M. kansasii was about 23,400 cal.mole-1. Experiments on the effect of temperature on protein synthesis showed that the temperature and time relationships required to complete and irreversibly inactivate protein synthesis correlated with thermal death. Judged from the data obtained, it was hypothesized that the initial cause of thermal death in the bacteria might be the heat inactivation of the protein synthetic machinery of the cells.

Arylsulfatases↗
PubMed1975

Use of cetylpyridinium chloride and sodium chloride for the decontamination of sputum specimens that are transported to the laboratory for the isolation of Mycobacterium tuberculosis.

A method is presented for the decontamination, liquefaction, and concentration of sputum specimens that are in transport more than 24 h. The method is inexpensive, and culture results compare well with those obtained with the accepted N-acetyl-L-cysteine and sodium hydroxide method for the isolation of tubercle bacilli. The working solution, 1% cetylpyridinium chloride and 2% sodium chloride, is mixed in equal volumes with sputum before the specimens are shipped. Tubercle bacilli remained viable after 8 days of exposure to this solution. Only Lowenstein-Jensen medium was used because the cetylpyridinium chloride in the inoculum remains active on 7H10 or other agar base media and partially inhibits the growth of tubercle bacilli.

Acetylcysteine↗
PubMed1974

Carotenoid pigments of Mycobacterium kansasii.

Partitioned between aqueous methanol and petroleum ether, the unsaponifiable pigments of Mycobacterium kansasii were all epiphasic. Thin-layer chromatography of these carotenoids showed that M. kansasii formed at least nine pigments. These pigments were identified by their chromatographic properties and spectral characteristics as phytoene, zeta-carotene, neurosporene, lycopene, leprotene, gamma-carotene, delta-carotene, alpha-carotene, and beta-carotene. Three additional pigmented spots on thin-layer chromatography found in trace amounts were possibly degradation products of the major carotenoids.

Carotenoids↗
PubMed1974

Biogenesis of beta-carotene in Mycobacterium kansasii.

The biogenesis of beta-carotene in the photochromogen Mycobacterium kansasii consists of two reactions. The first reaction is photochemical, and is dependent on the wavelength of the incident light and on oxygen but is independent of temperature. The second reaction does not require illumination, and is dependent on the temperature and on oxygen. The latter, or dark reaction, requires the synthesis of new protein, and was shown to have the characteristics of an inducible system. Carotenogenesis was stimulated by incident light of wavelengths of 420, 540, and 650 nm. Immediately after illumination there was an increase in the synthesis of ribonucleic acid and beta-carotene accumulation started after a lag of 8 to 10 min. The synthesis of beta-carotene exhibited temperature dependence with an optimum of about 36 C.

Acetates↗
PubMed1972

Effect of isoniazid on the in vivo mycolic acid synthesis, cell growth, and viability of Mycobacterium tuberculosis.

When an actively growing culture of the H37Ra strain of Mycobacterium tuberculosis was exposed to isoniazid at a concentration of 0.5 mug/ml, the cells began to lose their ability to synthesize mycolic acids immediately. After 60 min, the cells had completely lost this ability. The synthesis of the three mycolate components-alpha-mycolate, methoxymycolate, and beta-mycolate-was inhibited. The viability of the isoniazid-treated cells was unaffected up to about 60 min of exposure, after which time there was a gradual decline in the viability to about 18% after 180 min. Correspondingly, growth of the drug-treated cells slowed down and stopped after 24 hr. The inhibition of the synthesis of mycolic acids was reversible if the drug was removed before the loss of viability set in. Incubation of the viable cells in the absence of the drug for 24 hr restored the mycolate synthesis. These results strongly suggest that the inhibition of the synthesis of the mycolic acids is closely associated with the primary mechanism of action of isoniazid on the tubercle bacilli. The sequence of events which leads to the loss of viability of cells exposed to isoniazid is described.

Carbon Radioisotopes↗
PubMed1972

Susceptibility of mycobacteria to rifampin.

The Mycobacterium species M. tuberculosis, M. avium-intracellulare, M. kansasii, M. marinum, M. scrofulaceum, M. fortuitum, M. terrae, and M. gordonae were analyzed for their susceptibility to rifampin. M. tuberculosis, M. kansasii, and M. marinum were susceptible to the antibiotic, and resistant populations developed as a result of the interplay of mutation and selection. The mutation rates (susceptibility --> resistance) were calculated to be 4.9 x 10(-10) and 1.7 x 10(-9) mutations per bacterium per generation in, respectively, M. kansasii and M. marinum. M. fortuitum was found to be naturally resistant to the antibiotic, whereas the nature of resistance in the other species was unclear and is discussed.

Drug Resistance, Microbial↗