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Biomedical subjects

H Ng

Publications and source records attributed to H Ng.

At least 37 records · Page 2Linked to original sources
PubMed1982

Development of high heat resistance of Arizona neotype by preincubation at 35 degrees C in media containing NaCl.

When cells of Arizona neotype were preincubated at 35 degrees C in a medium containing NaCl (1 to 10%), they were found to be much more heat resistant upon being tested at 57 degrees C in a Trypticase (BBL Microbiology Systems) soy-yeast extract broth medium containing 10% NaCl than cells that had not been preincubated. Although no growth takes place during preincubation in the presence of 10% NaCl, some metabolic activity is necessary, since the presence of 2,4-dinitrophenol during incubation reduced the amount of gain in heat resistance. Incubation in the presence of N2, instead of air, abolished the effect. Chloramphenicol and rifampin, however, had no effect. Preincubated cells were just as heat resistant when separated by centrifugation and suspended in a fresh medium as when suspended in the incubated supernatant liquid. Conversely, the incubated supernatant liquid did not confer increased heat resistance upon unincubated cells. The increase in heat resistance, therefore, is probably a result of the salt osmotically plasmolyzing the cells by removing intracellular water, thus rendering the cellular contents more stable to heat. It is not known, however, why metabolic activity is necessary.

2,4-Dinitrophenol↗
PubMed1980

A combined defect of three mitochondrial carboxylases presenting as biotin-responsive 3-methylcrotonyl glycinuria and 3-hydroxyisovaleric aciduria.

A child with a history of episodes of metabolic acidosis was found to excrete 3-hydroxyisovaleric acid and 3-methylcrotonylglycine. These metabolites disappeared following the administration of biotin. The specific activities of propionyl CoA carboxylase, 3-methylcrotonyl CoA carboxylase and pyruvate carboxylase were found to be low in skin fibroblasts cultured in the absence of added biotin. With the addition of biotin, the specific activity of all three carboxylases returned to normal, that of 3-methylcrotonyl CoA carboxylase ahowing the greatest sensitivity to biotin.

Acidosis↗
PubMed1980

Viability of Mycobacterium leprae after multiplication in mice.

To measure the rate at which Mycobacterium leprae are killed in the course of the mouse footpad infection after the maximum of multiplication has been achieved, M. leprae were harvested shortly before and at intervals after multiplication had reached the level of 10(6) organisms per footpad, serially diluted, and inoculated into the footpads of passage mice. Beginning 1 year later, foot-by-foot harvests of M. leprae were performed from passage mice, and the proportion of viable organisms in the passage inocula was calculated by means of a most-probable-number calculation. In addition, the proportion of solidly staining M. leprae was measured in the passage inocula. The proportion of viable M. leprae in the passage inocula was found to decrease with the time after multiplication to 10(6) organisms per footpad of donor mice; the half-time of loss of viable M. leprae was 25 days. The proportion of solidly staining organisms appeared to be directly related to the proportion of viable organisms, as measured by mouse passage, and inversely proportional to the time after multiplication to 10(6) organisms per footpad.

Animals↗
PubMed1980

Survival of BALB/c mice after intraperitoneal infection with Mycobacterium lepraemurium.

In an attempt to develop a single, quantitative method of studying the disease that follows infection of susceptible mice with Mycobacterium lepraemurium, survival of BALB/c mice was measured as a function of time following i.p. inoculation with the organisms. Survival was found to be inversely related to the challenge dose of M. lepraemurium and unrelated to the organ-source of the organisms; survival was prolonged by treatment with isoniazid. Mice infected with M. lepraemurium were protected against i.v. challenge with M. marinum administered early in the disease, whereas they demonstrated enhanced susceptibility to the same challenge administered later. Conversely, prior M. marinum infection of mice in the hindfoot pad conferred protection against subsequent challenge with M. lepraemurium.

Animals↗
PubMed1980

Protection of mice by intraperitoneal vaccination against challenge in the foot pad with Mycobacterium marinum.

In a study of local infection of mice with Mycobacterium marinum, heat-killed M. marinum suspended either in Hanks' balanced salt solution or in Freund's incomplete adjuvant was administered i.p. to BALB/c mice. The mice were challenged in the hind foot pad 3, 7, or 14 days thereafter with 5 x 10(3) viable M. marinum. At every time interval, killed M. marinum in the saline medium conferred modest protection against the challenge infection, whereas the antigen suspended in adjuvant conferred protection only when the challenge was administered 14 days after vaccination. Freund's incomplete adjuvant appeared to enhance the infection and to minimize the immune response to the antigen.

Animals↗
PubMed1979

Pasteurization of salted whole egg inoculated with Arizona or Salmonella.

Recently, Arizona bacteria, close relatives of Salmonella, were recovered from salted whole egg that had been pasteurized by the presently recommended process of 63.3 degrees C (146 degrees F) for 3.5 min. Because of this and the fact that the heat resistance of Arizona in salted whole egg had not been determined, the present study was undertaken. Arizona or Salmonella, grown in Trypticase soy broth supplemented with 2% yeast extract in Fernbach flasks covered with aluminum foil over cotton and guaze at 35 degrees C with shaking at 176 rpm for about 96 h, were found to have the greatest degree of heat resistance. As expected, these cells, when inoculated into salted whole egg at 10(7) cells per ml, survived heating at 63.3 degrees C (146 degrees F) for 3.5 min in a two-phase slug flow heat exchanger. To consistently achieve a 7-log kill of typical Salmonella or Arizona, a treatment of 67 degrees C (152.6 degrees F) for 3.5 min was required. However, if a 7-log kill is mandatory, it remains to be determined whether this process affect the functional properties of this product.

Eggs↗
PubMed1975

The interactions of thrombin with borosilicate glass surfaces.

Borosilicate glass (G) and commercial poly(methyl methacrylate) (PMM) surfaces were examined at pH 7, monovalent ionic strength 0.14 and 22 degrees C. Thrombin concentrations ranged from 6 X 10(-9) to 5.2 X 10(-8)M. Decreases in thrombin concentration in 10 ml vessles were determined by clotting time assay. Adsorption to PMM vessels is small. These were examined to establish the validity of the method. For G-vessels, the terminations of initial rapid decreases, associated with adsorption equilibrium, are accounted for mainly by an average isotherm having an association constant of 1.8 X 10(7) l./mol. Adsorption equilibrium is accompanied by a slower rate of decrease consistent with the surface denaturation of 2.5%/min of adsorbed molecules. Molecules remaining adsorbed to the surfaces of 1 mm i.d. G-capillaries were examined using the sequence of thrombin adsorption, buffer washing for times tw, removal of buffer and introduction of a fibrinogen aliquot for determination of effective surface thrombin concentration by a capillary clotting time. Most adsorbed molecules (less than 90%) essentially desorb within tw = 2 min, a second class (greater than 8%) desorb in tw similar to 30 min, and members of additional classes are still present after tw = 1440 min. For all of the properties examined, there is a small variance between vessels taken at the same time from the same batch, and a larger variance between groups of vessels taken at different times from the same batch or from different batches.

Adsorption↗
PubMed1975

Death of Staphylococcus aureus in liquid whole egg near pH 8.

Incubating and shaking Staphylococcus aureus in liquid whole egg causes a decline in viability. During the period of agitation, the natural pH of the egg rises from about 7.2 to between 8.0 and 8.2 as a result of a loss of carbon dioxide. However, if the pH of the egg is prevented from rising, either by not shaking or by addition of a buffer, S. aureus will grow. The cause of death is traced to the presence of lysozyme of egg white. Interestingly, the action of lysozyme is not attributable to its bacterial lytic property but, instead, to the basicity of the lysozyme molecule. This conclusion is supported by the fact that the lytic property of lysozyme is known to have its optimal activity near neutrality and by the finding that protamine sulfate, a nonenzymatic basic polypeptide, also caused death of S. aureus at pH 8.0 but not at 7.0. It was postulated that the rise in pH renders the bacterial cells more negatively charged, so that in the presence of positively charged molecules like lysozyme or protamine sulfate a complex is formed, agglutinating the cells.

Carbon Dioxide↗
PubMed1975

Susceptibility of thymectomized and irradiated mice to challenge with several organisms and the effect of dapsone on infection with Mycobacterium leprae.

B6C3F1 mice that had been thymectomized at 8 to 12 weeks of age, subjected to 950 R of whole-body X irradiation, and transfused with syngeneic bone marrow were challenged in a footpad with Mycobacterium leprae or M. marinum, or intravenously or intraperitioneally with Listeria monocytogenes. Also, mice inoculated with M. leprae in a hind footpad were administered dapsone in the mouse chow. The thymectomized-irradiated (T + R) mice did not survive as well as non-thymectomized mice when housed in the vivarium with no special precautions, but survived sufficiently well to permit the completion of some long-term experiments. M. leprae multiplied to a higher "ceiling" and survived longer in the T + R mice than in the non-thymectomized controls. But a ceiling to multiplication of M. leprae was imposed, and finally the organisms were killed. The histopathological appearance of the footpad tissues, studied by electron microscopy, was consistent with the measurements of bacterial numbers and viability. Swelling of the footpad after local inoculation with M. marinum was greater in T + R mice than in non-thymectomized controls. Similarly, the number of L. monocytogenes following intravenous challenge was greater in the spleens of T + R than of non-thymectomized mice, and the survival of the T + R mice was impaired after intraperitoneal challenge with L.monocytogenes, compared to the survival of non-thymectomized mice. None of these differences was striking, suggesting that these T + R mice had retained or regained some immune competence. The effects of dapsone treatment of T + R mice inoculated with M. leprae were much the same as those of treatment of non-thymectomized mice. Because these T + R mice were not greatly immunosuppressed, they would not have provided a model of human lepromatous leprosy suitable for chemotherapeutic studies.

Animals↗
PubMed1973

Analogy of Mycobacterium marinum disease to Mycobacterium leprae infection in footpads of mice.

Because it appeared likely that the disease process that follows inoculation of footpads of mice with Mycobacterium marinum might serve as a useful model of mouse footpad infection with M. leprae for immunological studies. an attempt was made to establish an analogy between the two processes. As a second objective, the adequacy of measurements of mouse footpad thickness as an index of the total number of M. marinum and of the number of viable M. marinum was determined. The evolution of M. marinum disease in the footpads of BALB/c mice was observed, and the influences of mouse age and sex and of inoculum size were measured. Mice were challenged with M. marinum in one footpad at several intervals after inoculation of the contralateral hind footpad with the same organism. In all of these experiments, mouse footpad thickness was noted to parallel multiplication of M. marinum during the phase of increasing footpad swelling. Cessation of bacterial multiplication was noted to occur just before maximal swelling had been achieved, and was followed by rapid loss of viable M. marinum. The total number of organisms and mouse footpad thickness decreased only slowly and incompletely. Analogy between M. marinum disease and M. leprae infection of the mouse footpad was established by the self-limited nature of both processes, and by similar patterns of protection against homologous and heterologous challenge conferred by the two processes.

Age Factors↗
PubMed1972

Factors affecting organic acid production by sourdough (San Francisco) bacteria.

Previous workers from this laboratory observed considerable variation in the proportions of acetic and lactic acids produced in pure broth culture as compared to consistently high proportions of acetic acid produced in the sourdough and flour suspension systems. In the latter the proportion of acetic acid was always in the range of 20 to 35% of the total, whereas in pure broth culture frequently less than 5% acetic acid was produced. In the natural environment, the sourdough bacteria, tentatively identified as lactobacilli, coexist with a yeast, Saccharomyces exiguus, and this study was undertaken to determine whether this yeast or flour ingredients including glucose or other factors were involved in this variable production of acetic acid. The proportion of acetic acid produced in broth culture on maltose, the preferred carbohydrate source, was found to depend almost entirely on the degree of aeration. Essentially anaerobic conditions, as obtained by thorough evacuation and flushing with CO(2) or N(2), resulted in very low (5% or less) proportions of acetic acid. Aerobic conditions, achieved by continuous shaking in cotton-plugged flasks, yielded high levels (23 to 39% of the total) of acetic acid. Similar effects of aeration were observed with glucose as the substrate, although growth was considerably slower, or in nonsterile flour suspension systems. It is theorized that, under aerobic conditions, the reduced pyridine nucleotides generated in the dissimilation of carbohydrate are oxidized directly by molecular oxygen, thereby becoming unavailable for the reduction of the acetyl phosphate intermediate to ethyl alcohol, the usual product of anaerobic dissimilation of glucose by heterofermentative lactic acid bacteria. Comparative studies with known strains of homo- and heterofermentative lactobacilli showed similar effects of aeration only on the heterofermentative strains, lending additional support to the tentative grouping by previous workers from this laboratory of the sourdough bacteria with the heterofermentative lactobacilli.

Acetates↗
PubMed1969

Heat resistance of Salmonella: the uniqueness of Salmonella senftenberg 775W.

Of approximately 300 cultures of Salmonella, representing 75 different serotypes, none was found to be as heat-resistant as S. senftenberg 775W. However, S. blockley 2004 was 5 times more heat-resistant and S. senftenberg 775W was 30 times more heat-resistant than S. typhimurium Tm-1, the reference strain in this study. All other strains of Salmonella tested, including 19 strains of S. senftenberg and 7 strains of S. blockley, had decimal reduction times at 57 C of about 1 min, equivalent to that of the reference organism, Tm-1. As observed in other bacterial species, strain 775W is more heat-sensitive in the log phase than in the stationary phase of growth. Cells from cultures grown at 44 C were more heat-resistant than those grown at either 35 or 15 C; the medium of growth, whether minimal or complex, made no appreciable difference in heat resistance. Cells from cultures limited by a carbon source were killed at a much slower rate than those limited by a nitrogen source and exhibited a 1-hr lag at 55 C before a significant rate of kill was attained. For any given set of growth conditions, strain 775W was always more heat-resistant than another strain of S. senftenberg, 197B, which has normal heat resistance.

Culture Media↗
PubMed1969

Effect of decreasing growth temperature on cell yield of Escherichia coli.

Studies of the relationship between yield coefficient and growth rate, as affected by temperature of growth, in Escherichia coli have shown that, over a wide range of temperature, yield is relatively constant until the specific growth rate falls below about 0.2 hr(-1), at which point the yield begins to fall off precipitously. No intermediates of glucose metabolism in a form utilizable at higher temperatures could be found in the medium, and no toxic product was produced which limited growth. At 10 C, 37% of the carbon from glucose-UL-(14)C was assimilated into cellular material, whereas, at 30 C, 53% was assimilated. Cells grown at 10 C contained more carbohydrate than did cells grown at 37 C, and the glycogen-to-protein ratio of cells grown at 10 C was approximately three times higher than that of cells grown at 37 C. Adenosine triphosphatase activities of cells grown at 10 and 35 C were similar. Growth rates on glucose, glycerol, and succinate were quite similar at 10 C, but at 35 C growth was most rapid on glucose and slowest on succinate. The data suggest that the decrease in yield with decrease in temperature is a result of uncoupling of energy production from energy utilization.

Adenosine Triphosphatases↗