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Biomedical subjects

L Amaral

Publications and source records attributed to L Amaral.

At least 37 records · Page 2Linked to original sources
PubMed1989

The post-antibiotic effect defined by bacterial morphology.

Three strains of Escherichia coli were incubated with either ciprofloxacin or ampicillin. Filamentation of bacteria was observed after 1-2 h. After 5 h of contact with either drug the percentage of filaments exceeded 90%. The organisms were washed and incubated on drug free medium. Antibiotics when bound to an enzyme render that enzyme inactive; upon removal of the organisms from the antibiotic, the synthesis of enzymes resumes. The period of time encompassing the inactive enzymatic state of the organism at the time of removal from the drug to the time that enzymes restore complete function is our definition of the post-antibiotic effect (pae). Bacterial morphology reflects the variations in activity of these enzymes. The pae was determined by both the morphology of the organisms and the current growth kinetic method. The presence of 10% filaments and 90% bacilli was selected to indicate the endpoint of the pae by morphological criteria. The pae by morphology was 4 h for ciprofloxacin and 3 h for ampicillin. By the growth kinetics method it was 2 h for ciprofloxacin and zero for ampicillin.

Ampicillin↗
PubMed1988

Trichomoniasis and campylobacteriosis in bulls in the Republic of Transkei.

Trichomonas foetus was demonstrated in 23/87 (26.4%) and Campylobacter fetus in 25/87 (28.7%) of bulls tested in Transkei. A total of 16/87 (18.39%) of bulls tested were positive for both Trichomonas foetus and Campylobacter fetus. Bulls from 14 sites in Transkei were tested and Trichomonas foetus was isolated at 9 of these sites. Campylobacter fetus was isolated at 10 of the 14 sites. The results indicate that both Trichomonas foetus and Campylobacter fetus are widespread throughout the cattle population in the Republic of Transkei and may account for infertility problems.

Age Factors↗
PubMed1986

Penicillin-binding site on the Escherichia coli cell envelope.

The binding of 35S-labeled penicillin to distinct penicillin-binding proteins (PBPs) of the "cell envelope" obtained from the sonication of Escherichia coli was studied at different pHs ranging from 4 to 11. At low pH, PBPs 1b, 1c, 2, and 3 demonstrated the greatest amount of binding. At high pH, these PBPs bound the least amount of penicillin. PBPs 1a and 5/6 exhibited the greatest amount of binding at pH 10 and the least amount at pH 4. With the exception of PBP 5/6, the effect of pH on the binding of penicillin was direct. Experiments distinguishing the effect of pH on penicillin binding by PBP 5/6 from its effect on beta-lactamase activity indicated that although substantial binding occurred at the lowest pH, the amount of binding increased with pH, reaching a maximum at pH 10. Based on earlier studies, it is proposed that the binding at high pH involves the formation of a covalent bond between the C-7 of penicillin and free epsilon amino groups of the PBPs. At pHs ranging from 4 to 8, position 1 of penicillin, occupied by sulfur, is considered to be the site that establishes a covalent bond with the sulfhydryl groups of PBP 5. The use of specific blockers of free epsilon amino groups or sulfhydryl groups indicated that wherever the presence of each had little or no effect on the binding of penicillin by PBP 5, the presence of both completely prevented binding. The specific blocker of the hydroxyl group of serine did not affect the binding of penicillin. These observations suggest that a molecule of penicillin forms simultaneous bonds between its S at position 1 and sulfhydryl groups of PBP 5 and between its C-7 and free epsilon amino groups of PBP 5.

Bacterial Proteins↗
PubMed1986

Penicillin-binding proteins of filaments of Escherichia coli induced by low concentrations of nalidixic acid, oxolinic acid, novobiocin or nitrofurantoin.

Nalidixic acid, novobiocin, oxolinic acid and nitrofurantoin, each at low concentrations, cause filamentation of Gram-negative bacilli. Filamentation induced by beta-lactam antibiotics has been correlated to the binding of these antibiotics to specific penicillin-binding proteins (PBPs) of the envelope of Gram-negative bacilli. The studies reported herein indicate that the former group of non-beta-lactam antibiotics do not bind to any of the PBPs of Escherichia coli. However, PBP 1a, PBP 4 and PBP 5/6 of the filaments induced by these agents are increased significantly.

Acyltransferases↗
PubMed1984

Helminth parasites of game in Transkei.

Opportunities have been taken to examine sundry game animals for parasites over the past 2 years. A host parasite check list is presented from which it may be noted that Oesophagostomum columbianum is recorded for the first time in the red hartebeest Alcelaphus buselaphus and Haemochus bedfordi for the first time in the eland Taurotragus oryx.

Animal Population Groups↗
PubMed1983

The effect of ascorbic acid on the human lymphocyte.

Human lymphocytes obtained from normal, healthy subjects were studied for their in vitro responses to ascorbic acid. Ascorbic acid inhibited the incorporation of 3H-uridine as well as the phytohaemagglutin-associated enhancement of 3H-thymidine incorporation.

Ascorbic Acid↗
PubMed1982

The radioactive thymidine incorporation method for the determination of antibiotic susceptibility of gram-negative bacilli.

The thymidine incorporation method was compared with the disc diffusion and broth dilution methods for determining the antibiotic susceptibility of Escherichia coli (233 strains), Proteus mirabilis (72 strains) and Klebsiella species (189 strains). The method measures changes in the rate of DNA synthesis of bacterial strains exposed to an antibiotic by comparing the amount of radioactive thymidine incorporated by these strains in relation to control strains. Good agreement was obtained between the results of the thymidine incorporation and disc diffusion methods for all antibiotics tested except streptomycin and tetracycline. Minimal inhibitory concentrations of antibiotics determined by the thymidine incorporation method after 3 and 5 hours were generally lower than those obtained after 24 hours by the conventional broth dilution procedure. The thymidine incorporation method may be potentially useful for determining the antibiotic susceptibility of bacteria a few hours after inoculation of a clinical specimen.

Anti-Bacterial Agents↗
PubMed1982

Sublethal concentrations of antibiotics, effects on bacteria and the immune system.

Biological specimens obtained from patients with infections that are treated with antibiotics at dosages that resulted in body fluid concentrations below those that are minimally inhibitory, exhibit abnormal forms of bacteria. Identical morphological changes can be induced in vitro when the parental normal forms of the bacteria. Identical morphological changes can be induced in vitro when the parental normal forms of the bacteria are exposed to subminimal concentrations of certain antibiotics. The phenomenon of induced abnormal morphology and ultrastructure has received consideration in terms of: (1) the relationship of the induced alterations of the specific bacterial species to the given antibiotic, (2) in vitro conditions required for antibiotic induced alterations, (3) the mechanisms of action; (4) immune responses to the abnormal forms, and (5) relationship between abnormal structure and the inhibition of bacterial replication. This review provides the reader with a description and the significance of current research in the above areas which together comprise the growing field of subinhibitory concentrations of antibiotics.

Anti-Bacterial Agents↗
PubMed1982

Responses of chronic lymphocytic leukemic lymphocytes to increasing concentrations of phytohemagglutinin during short-term culture.

Lymphocytes obtained from CLL patients containing high and low peripheral lymphocyte cell counts were cultured in the absence and presence of increasing concentrations of phytohemagglutinin for periods of up to 2 h. Lymphocytes from patients with low cell counts (less than 50,000/mm3) were stimulated to incorporate 3H-uridine during the 1st h of culture by concentrations of PHA ranging from 1 to 32 microgram/ml. Under identical conditions, lymphocytes from patients with high cell count (greater than 50,000/mm3) were barely affected. During the 2nd h of culture the above concentrations stimulated to a lesser degree the former group of lymphocytes, whereas it inhibited incorporation by the latter group. The results obtained suggest a qualitative difference in the response of CLL lymphocytes to PHA in accordance with the progression of the disease.

Cells, Cultured↗
PubMed1981

Cortisol resistant RPMI-1788 lymphocytes become sensitive to cortisol subsequent to a 24-h incubation period in medium containing purified human transcortin.

RPMI-1788 lymphocytes (a human cell line) are resistant to cortisol in vitro. Prior incubation for a minimum of 24 h in a medium which contains purified human transcortin at a concentration of 50 micrograms/ml renders these cells sensitive to the inhibitory action of cortisol as regards the synthesis of DNA. Only the transcortin-exposed cells contain a cortisol binding species whose sedimentation behavior in a sucrose gradient is identical to that of transcortin.

Cells, Cultured↗
PubMed1981

The effect of steroids on the synthesis of RNA by isolated T and B lymphocytes of normal donors and patients with chronic lymphocytic leukemia.

T- and B-lymphocyte populations were isolated from peripheral blood of 11 patients who had chronic lymphocytic leukemia (CLL) and four normal healthy donors. The isolated T and B cells were cultured in the absence and presence of cortisol, dexamethasone, beta-estradiol, testosterone, and progesterone, and the effects of these steroids on the synthesis of RNA was investigated. T and B cells of the CLL group were significantly more inhibited in the synthesis of RNA than the respective cells of the normal control group. The individual responses of T and B cells to each of the steroids differed in both the CLL and control groups, as well as between the respective subpopulations of each of the groups. Analysis of th LDH isoenzyme patterns of T and B cells of each group suggested major differences in the distribution of their LDH isoenzymes.

Aged↗
PubMed1980

Lymphopenic response of patients presenting with chronic lymphocytic leukemia associated with carcinoma of the prostate to diethylstilbestrol: correlation of response to the in vitro synthesis of RNA by patient lymphocytes and its relationship to transcortin.

Three patients with chronic lymphocytic leukemia (CLL) and carcinoma of the prostate were treated for the latter condition with diethylstilbestrol (DES). All three patients responded with rapid reductions in their peripheral white counts. The previously observed lymphocytic infiltration of the bone marrow of one patient was not evident after three months of DES treatment. The response of this patient to DES correlates well with the enhanced level of plasma transcortin subsequent to treatment. Treatment of this patient with DES alters the ability of peripheral lymphocytes to incorporate radioactive uridine into RNA as well as the in vitro response to either cortisol or beta-estradiol.

Carcinoma↗
PubMed1976

Electrophoretic abnormalities in chronic lymphocytic leukemia and cancer sera.

It was previously shown (Am J Clin Pathol 55: 65-67, 1971) that sera from patients with chronic lymphocytic leukemia (CLL) produce a characteristic pattern on disk-acrylamide gels. Other observations indicating the presence of immunosuppressive proteins in the sera of patients with cancer suggested the search for characteristic protein patterns employing the same technic. Utilizing sera from patients with various types of malignancies and appropriate controls, the results appear to indicate that there is a consistent and distinctive pattern to the gels. The nature of the (different) protein(s) remains to be elucidated.

Adenocarcinoma↗
PubMed1976

Placenta, transcortin, and localized immune response.

The syncytiotrophoblastic cells of the human placenta contain a cytoplasmic protein recognized by fluorescein-labeled transcortin-specific antibody. Purification of this protein from human placenta, by those methods employed for the purification of human plasma transcortin, yielded a protein that exhibited antigenic and biochemical similarity to plasma transcortin. Placental transcortin differs from plasma transcortin in that it has a smaller sedimentation coefficient (3S vs 3.75S) and binds cortisol less strongly. This purified protein is able to block the phytohemagglutinin response of maternal lymphocytes even more than serum transcortin. It is postulated that the biological role may be that of inhibiting the maternal cell-mediated immune response to the presence of the antigenic conceptus.

Chromatography, DEAE-Cellulose↗