Search PubMed⌕ Search

Biomedical subjects

M Alexander

Publications and source records attributed to M Alexander.

At least 181 records · Page 10Linked to original sources
PubMed1988

Role of protozoa in microbial acclimation for mineralization of organic chemicals in sewage.

The role of protozoa in affecting the length of the acclimation period for the mineralization of organic compounds in sewage was investigated. The acclimation periods for the mineralization of 2 ng of p-nitrophenol, 100 ng of 2,4-dichlorophenoxyacetic acid, and 100 ng of 2,4-dichlorophenol per milliliter were markedly shortened or eliminated when the indigenous protozoa were inhibited with cycloheximide and nystatin. The extent of mineralization of the test compounds decreased when the protozoa were suppressed. Inhibition of the protozoa increased the total number of bacteria and the density of organisms able to mineralize 2 ng of p-nitrophenol/mL of sewage. Addition of Tetrahymena thermophila to sewage in which the indigenous protozoa were not active lengthened the acclimation period for the mineralization of p-nitrophenol. The addition of T. thermophila to a culture containing a low density of a p-nitrophenol-degrading Pseudomonas sp. did not affect the acclimation period prior to mineralization of the substrate, but the ciliate increased the acclimation period in the presence of high densities of Enterobacter aerogenes added as an alternative prey species. We suggest that protozoan grazing may be responsible for the acclimation period prior to the mineralization of certain organic compounds in sewage.

Animals↗
PubMed1988

Polysomnographic studies of infants who subsequently died of sudden infant death syndrome.

The polygraphic findings from 11 future victims of sudden infant death syndrome (SIDS) are reported and compared with those of matched pairs of control infants. The recordings had been done to alleviate parental anxiety about sleep apnea. Four infants had siblings who were victims of SIDS. Two infants were studied 3.5 to 9.5 weeks before their deaths because of an unexplained apparent life-threatening event that had occurred during sleep. For each victim of SIDS, two control infants were selected from the 2,000 infants who had been tested in the same hospitals. They were matched for sex, gestational age, postnatal age, and weight at birth with the SIDS victims. Their polygraphic recordings had been performed within similar conditions. Each record was allocated a random code number and was analyzed without knowledge of the patient's identity by two independent scorers. Most sleep and cardiorespiratory variables studied did not differentiate SIDS victims from control infants. Only four variables significantly characterized the future SIDS victims: the maximal duration of central apneas, the number of sighs followed by a central apnea, the presence of obstructive apneas, and the presence of mixed apneas. Central apneas were longer during all sleep states in the SIDS victims compared with their matched controls, but none exceeded 14 seconds. Sighs immediately followed by an apnea were significantly less frequent in the future SIDS group. Obstructive and mixed sleep apneas were seen in eight of 11 SIDS victims and in only three of 22 control infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1988

[Frequency and clinical relevance of delta virus infection in HBsAg carriers in the Berlin area].

The frequency of delta virus infection, immunoserological parameters and degree of liver inflammation were studied in 190 HBsAg carriers in the Berlin area from 1976 to 1986. Delta infection was detected in one of 50 HBsAg carriers (2%) in the period from 1976 to 1980. In contrast 19 of 140 HBsAg carriers (14%) with delta infection were found in the period from 1981 to 1986. This group included 12 Germans, 5 Turks and 2 Italians. Only 6 of these subjects belonged to a so-called risk group: 3 drug addicts, 2 homosexuals and 1 hemophiliac. Eighteen of the 20 patients with HDV infection showed progressive liver disease in the follow-up period. Nine cases developed complete liver cirrhosis over five years. Variable transaminase levels and elevation of immunoglobulin G were recorded. Humoral autoimmune phenomena were rarely observed. The increasing frequency of HDV infection in the Berlin area is presumably related to tourism, national origin and membership in specific risk groups. The data in our study underline the importance of effective prophylaxis by active immunization with HBsAg vaccines.

Adult↗
PubMed1987

Metabolism of native and acetylated low density lipoproteins in squirrel monkeys with emphasis on aortas with varying severities of atherosclerosis.

We studied the clearance of 131I-labeled native low density lipoproteins (LDL) and 125I-acetyl LDL from the blood of hypercholesterolemic and atherosclerotic squirrel monkeys which had been fed a semipurified diet supplemented with cholesterol for 3 years and from control monkeys which had been fed the same diet without cholesterol. In agreement with previous observations in other species, acetyl LDL left the circulation much more rapidly than native LDL. The cholesterol supplemented monkeys removed native 131I-LDL to the liver, the major site of clearance of both LDL forms, more slowly than controls. The overall clearance of 125I-acetyl LDL was similar for the two groups. The aortic intima plus inner media (AIM) cleared both LDL forms much more slowly than other organs, and the ratio of acetyl LDL to native LDL cleared was quite high. The outer media (OM) showed less selectivity for acetyl LDL than the AIM. While LDL clearance by the OM was not affected by diet, the LDL clearance per g of AIM tissue was increased by 2-fold for both native and acetyl LDL in the cholesterol supplemented monkeys. These monkeys also had a 3-fold increase in AIM weight (due to intimal and subintimal thickening), which resulted in a 6-fold increase in the total LDL cleared by the AIM. The clearance of both LDL forms by the AIM correlated with three indices of atherosclerosis: intimal thickness, AIM weight, and AIM cholesterol concentration. The correlations were higher in the case of acetyl LDL clearance which may be due to the high affinity of the acetylated form for macrophages.

Animals↗
PubMed1987

Effects of maternal and long-term postnatal protein malnutrition on brain size and composition in rhesus monkeys.

Rhesus monkeys consumed purified diets that supplied either low or adequate levels of protein (3.8 vs. 13.9% of energy as casein) from birth until approximately 10 yr of age. A subgroup (PN) was born of mothers that also received low or control levels of protein throughout pregnancy. The deprived groups weighed significantly less than corresponding control groups. Weights of the total brain, cerebellum and brain stem were significantly reduced in the PN deprived group. Analysis of variance also indicated that low protein diets produced a significant reduction in cerebral weight. The concentrations of DNA, protein and eight different lipids from seven different sites in the central and peripheral nervous system were not greatly affected by diet. The total content of lecithin and phosphatidylethanolamine was significantly depressed in some parts of the deprived monkey brains. The deficits in brain weight of the PN group (10% for the cerebrum, 13% for the cerebellum and 18% for the brain stem) were very similar to those observed previously in 1-mo-old monkeys born of protein-deprived mothers and fed low protein diets postnatally. On the other hand, monkeys born of adequately nourished mothers and then fed low protein diets from birth up to 12 yr showed no deficit in brain weight despite reduction in body weight to less than half of control values.

Animals↗
PubMed1987

Serological assessment of HBcAg and HBV DNA: its prognostic relevance in acute hepatitis B.

Treatment of serum precipitates with sodium thiocyanate in patients with hepatitis B virus (HBV) replication results in liberation of circulating hepatitis core antigen (HBcAg) which can be demonstrated radioimmunologically. Follow-up investigations were performed in 80 patients with acute hepatitis B. Sera were examined for HBcAg. HBV DNA and conventional HBV markers. At the time of admission to hospital 34 of 80 (42%) patients were HBeAg positive. Twenty-six (76%) of the 34 HBcAg positive patients were HBV DNA positive, and circulating HBcAg was detectable in 25 of 34 (73%) HBcAg positive cases. In patients with uncomplicated courses of acute hepatitis B the serological HBcAg assay and HBV DNA became negative 1 to 8 weeks before elimination of HBeAg and up to 12 weeks earlier than the sera became negative for HBsAg. Five patients (6%) showed transition to chronic hepatitis B with persistence of HBsAg, HBeAg, HBV DNA and HBcAg in serum. One patient with acute hepatitis B and development of chronic hepatitis suffered from acquired immunodeficiency syndrome and showed delayed formation of anti-HBc. In this case uncomplexed HBcAg was demonstrable during the acute phase of hepatitis B. With the appearance of anti-HBc HBcAg circulated in a complexed form. The data indicate that serological determinations of HBcAg and HBV DNA can serve as prognostic markers in the early phase of acute hepatitis B. The demonstration of uncomplexed HBcAg in serum of a patient with inadequate formation of anti-HBc supports the hypothesis that circulating HBcAg is usually complexed by specific antibodies.

Acute Disease↗
PubMed1987

Kinetics of p-nitrophenol mineralization by a Pseudomonas sp.: effects of second substrates.

The kinetics of simultaneous mineralization of p-nitrophenol (PNP) and glucose by Pseudomonas sp. were evaluated by nonlinear regression analysis. Pseudomonas sp. did not mineralize PNP at a concentration of 10 ng/ml but metabolized it at concentrations of 50 ng/ml or higher. The Ks value for PNP mineralization by Pseudomonas sp. was 1.1 micrograms/ml, whereas the Ks values for phenol and glucose mineralization were 0.10 and 0.25 micrograms/ml, respectively. The addition of glucose to the media did not enable Pseudomonas sp. to mineralize 10 ng of PNP per ml but did enhance the degradation of higher concentrations of PNP. This enhanced degradation resulted from the simultaneous use of glucose and PNP and the increased rate of growth of Pseudomonas sp. on glucose. The Monod equation and a dual-substrate model fit these data equally well. The dual-substrate model was used to analyze the data because the theoretical assumptions of the Monod equation were not met. Phenol inhibited PNP mineralization and changed the kinetics of PNP mineralization so that the pattern appeared to reflect growth, when in fact growth was not occurring. Thus, the fitting of models to substrate depletion curves may lead to erroneous interpretations of data if the effects of second substrates on population dynamics are not considered.

Biodegradation, Environmental↗
PubMed1987

Role of dissolution rate and solubility in biodegradation of aromatic compounds.

Strains of Moraxella sp., Pseudomonas sp., and Flavobacterium sp. able to grow on biphenyl were isolated from sewage. The bacteria produced 2.3 to 4.5 g of protein per mol of biphenyl carbon, and similar protein yields were obtained when the isolates were grown on succinate. Mineralization of biphenyl was exponential during the phase of exponential growth of Moraxella sp. and Pseudomonas sp. In biphenyl-supplemented media, Flavobacterium sp. had one exponential phase of growth apparently at the expense of contaminating dissolved carbon in the solution and a second exponential phase during which it mineralized the hydrocarbon. Phase-contrast microscopy did not show significant numbers of cells of these three species on the surface of the solid substrate as it underwent decomposition. Pseudomonas sp. did not form products that affected the solubility of biphenyl, although its excretions did increase the dissolution rate. It was calculated that Pseudomonas sp. consumed 29 nmol of biphenyl per ml in the 1 h after the end of the exponential phase of growth, but 32 nmol of substrate per ml went into solution in that period when the growth rate had declined. In a medium with anthracene as the sole added carbon source, Flavobacterium sp. converted 90% of the substrate to water-soluble products, and a slow mineralization was detected when the cell numbers were not increasing. Flavobacterium sp. and Beijerinckia sp. initially grew exponentially and then arithmetically in media with phenanthrene as the sole carbon source. Calculations based on the growth rates of these bacteria and the rates of dissolution of phenanthrene suggest that the dissolution rate of the hydrocarbon may limit the rate of its biodegradation.

Biodegradation, Environmental↗
PubMed1987

Explanations for the acclimation period preceding the mineralization of organic chemicals in aquatic environments.

A study was conducted of possible reasons for acclimation of microbial communities to the mineralization of organic compounds in lake water and sewage. The acclimation period for the mineralization of 2 ng of p-nitrophenol (PNP) or 2,4-dichlorophenoxyacetic acid per ml of sewage was eliminated when the sewage was incubated for 9 or 16 days, respectively, with no added substrate. The acclimation period for the mineralization of 2 ng but not 200 ng or 2 micrograms of PNP per ml was eliminated when the compound was added to lake water that had been first incubated in the laboratory. Mineralization of PNP by Flavobacterium sp. was detected within 7 h at concentrations of 20 ng/ml to 2 micrograms/ml but only after 25 h at 2 ng/ml. PNP-utilizing organisms began to multiply logarithmically after 1 day in lake water amended with 2 micrograms of PNP per ml, but substrate disappearance was only detected at 8 days, at which time the numbers were approaching 10(5) cells per ml. The addition of inorganic nutrients reduced the length of the acclimation period from 6 to 3 days in sewage and from 6 days to 1 day in lake water. The prior degradation of natural organic materials in the sewage and lake water had no effect on the acclimation period for the mineralization of PNP, and naturally occurring inhibitors that might delay the mineralization were not present. The length of the acclimation phase for the mineralization of 2 ng of PNP per ml was shortened when the protozoa in sewage were suppressed by eucaryotic inhibitors, but it was unaffected or increased if the inhibitors were added to lake water.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1986

Reye's syndrome. Salicylate metabolism, viral antibody levels, and other factors in surviving patients and unaffected family members.

To investigate possible etiologic factors for Reye's syndrome (RS), five survivors and their unaffected family members were studied. This study showed low salicylate levels among the patients with RS compared with siblings and parents when challenged with three doses of aspirin. Thus, the patients with RS, three to ten years after having had RS, exhibited normal or increased ability to metabolize aspirin. We found significantly higher antibody levels to influenza A and varicella among the patients with RS, further supporting the importance of these viral infections in the etiology of the syndrome.

Adolescent↗
PubMed1986

Anomalies in mineralization of low concentrations of organic compounds in lake water and sewage.

The rates of mineralization of nitrilotriacetic acid (NTA), 2,4-dichlorophenoxyacetic acid (2,4-D), p-nitrophenol, aniline, and isopropyl N-phenylcarbamate (IPC) at one or more concentrations ranging from 100 pg/ml to 1.0 microgram/ml were proportional to chemical concentrations in samples of three lakes. The rates at 100 pg of NTA, 2,4-D, p-nitrophenol, and aniline per ml in samples of one or more lakes were less than predicted, assuming the rates were linearly related to the concentration. Neither NTA nor 2,4-dichlorophenol at 2.0 ng/ml was mineralized in some lake waters, but higher levels of the two chemicals were converted to CO2 in samples of the same waters. In samples from two lakes, little or no mineralization of IPC or 2,4-D occurred at 1.0 microgram/ml, but 10 ng/ml or lower levels of the herbicides were mineralized. The mineralization in sewage of 1.0 microgram of NTA per ml was biphasic; about 20% of the substrate was mineralized in 20 h, and mineralization was only reinitiated after a period of 130 h. The biphasic transformation was not a result of the accumulation of organic products, and it was still evident if protozoan activity was inhibited. NTA also underwent a biphasic mineralization in lake waters, and the biphasic pattern was not altered by additions of growth factors and inorganic nutrients. From 40 to 60% of the carbon of aniline added to lake water at levels of 100 pg/ml to 1.0 microgram/ml was mineralized, but more than 90% of the carbon of NTA, 2,4-D, or p-nitrophenol added to lake water at 10 ng/ml or 1.0 microgram/ml was mineralized.(ABSTRACT TRUNCATED AT 250 WORDS)

2,4-Dichlorophenoxyacetic Acid↗
PubMed1986

Kinetics of mineralization of organic compounds at low concentrations in soil.

The kinetics of mineralization of 14C-labeled phenol and aniline were measured at initial concentrations ranging from 0.32 to 5,000 ng and 0.30 ng to 500 micrograms/g of soil, respectively. Mineralization of phenol at concentrations less than or equal to 32 ng/g of soil and of aniline at all concentrations began immediately, and the curves for the evolution of labeled CO2 were biphasic. The patterns of mineralization of 4.0 ng of 2,4-dichlorophenol per g of soil and 20 ng of nitrilotriacetic acid per g of soil were similar to the patterns for phenol and aniline. The patterns of mineralization of 1.0 to 100 ng of p-nitrophenol and 6.0 ng of benzylamine per g of soil were also biphasic but after a short apparent lag period. The curves of CO2 evolution from higher concentrations of phenol and p-nitrophenol had increasing apparent lag phases and were S-shaped or linear. Cumulative plots of the percentage of substrate converted to CO2 were fit by nonlinear regression to first-order, integrated Monod, logistic, logarithmic, zero-order, three-half-order, and two-compartment models. None of the models of the Monod family provided the curve of best fit to any of the patterns of mineralization. The linear growth form of the three-half-order model provided the best fit for the mineralization of p-nitrophenol, with the exception of the lowest concentrations, and of benzylamine. The two-compartment model provided the best fit for the mineralization of concentrations of phenol below 100 ng/g, of several concentrations of aniline, and of nitrilotriacetic acid. It is concluded that models derived from the Monod equation, including the first-order model, do not adequately describe the kinetics of mineralization of low concentrations of chemicals added to soil.

Aniline Compounds↗