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Biomedical subjects

D A Mitchison

Publications and source records attributed to D A Mitchison.

At least 73 records · Page 4Linked to original sources
PubMed1992

Counts of viable tubercle bacilli in sputum related to smear and culture gradings.

Pairs of sputum specimens obtained pre-treatment from 166 smear-positive patients with pulmonary tuberculosis were examined by direct smear, culture on Löwenstein-Jensen medium after decontamination by the Petroff method, and by quantitative colony counting on selective 7H11 medium after digestion with dithiothreitol. The selective medium counts ranged from no growth to 8.3 log10 cfu/ml with the largest numbers in the range 3.5-7.0 log10 cfu/ml. Although there was overlap in counts between specimens with negative and positive direct smears, a specimen with a count of 4.0 log10 cfu/ml or more was likely to have a positive smear while a negative smear was likely if the count was lower. This demarcation value should be increased to 4.5 log10 cfu/ml to account for under-estimation in the selective medium counts. The corresponding demarcation estimate for LJ cultures was 80 colonies. In distinguishing between patients in the bacterial contents of their sputum, the selective medium counts were better than the gradings of either LJ cultures or direct smears.

Bacteriological Techniques↗
PubMed1991

Efficacy of intermittent pyrazinamide in experimental murine tuberculosis.

CFLP mice were infected intravenously with Mycobacterium tuberculosis strain H37Rv and the progress of chemotherapy was followed by counts of viable bacilli in the lung and spleen. After spleen counts had reached log10 7.0, 12 experimental groups, each containing 10 mice, were treated for 8 weeks with pyrazinamide (PZA) given in mean daily dosages of 100, 200 or 400 mg/kg/day, with the interval between the doses within each dosage group being 1, 2, 4 or 8 days. All mice were also given 25 mg isoniazid/kg daily. An increase in the mean daily dosage from 100 mg PZA/kg to 400 mg PZA/kg resulted in a decrease of spleen viable counts at the end of treatment from log10 4.2 to log10 3.8. The organ counts, averaged over the full dosage range, were little altered by spacing out the interval between doses from 1-4 days, while increasing dose size proportionately: the counts with low mean dosages tended, however, to decrease (indicating improved efficacy) while those with high mean dosages increased (P less than 0.001). Counts increased when the interval was 8 days. Spacing out the doses while keeping the dose size constant resulted in progressive loss of efficacy. These findings suggest that, if PZA is given intermittently, the size of the dose should be increased, though not quite proportionately, to maintain full efficacy. Even with such an increase in dose, however, once weekly treatment would be less effective.

Animals↗
PubMed1990

In vitro activities against mycobacteria of two long-acting rifamycins, FCE22807 and CGP40/469A (SPA-S-565).

The in vitro activities of two new long-acting rifamycins, FCE22807 a derivative of FCE22250, and CGP40/469A (SPA-S-565) were studied. When compared with rifampicin, the minimal inhibitory concentrations (MIC) against Mycobacterium tuberculosis of both were 4 times lower but neither was particularly active against rifampicin-resistant strains of M. tuberculosis nor against M. avium-intracellulare-scrofulaceum complex strains. A drug is likely to be particularly effective in widely spaced intermittent dosage if it has a long half-life and high bactericidal activity. When tested against M. tuberculosis in the logarithmic and in the stationary phase of growth, FCE22807 was amongst the most bactericidal of the rifamycins while CGP40/469A had little bactericidal activity.

Anti-Bacterial Agents↗
PubMed1990

Serodiagnosis of tuberculosis using an ELISA with antigen 5 and a hemagglutination assay with glycolipid antigens. Results in patients with newly diagnosed pulmonary tuberculosis ranging in extent of disease from minimal to extensive.

Hemagglutination tests with three glycolipid antigens, A1, B1, and C, and ELISA with antigen 5 were done on serum from Chinese patients with pulmonary tuberculosis and from normal subjects in Hong Kong. Tests with all four antigens were of similar efficiency, giving positive results in 30 to 52% of 88 smear-positive patients, in 16 to 22% of 37 smear-negative, culture-positive patients, in 5 to 13% of 76 culture-negative patients with radiologically active disease, in 5 to 11% of 217 culture-negative patients with inactive disease, and in 1 to 4% of 140 normal subjects. If tests were combined so that an overall positive was scored when all tests were positive, there was worse discrimination between patients and normal subjects; however, as suggested by the poor correlation between the results with pairs of the tests, better discrimination was obtained if an overall positive was scored when any of the tests was positive. A positive result in any of the four tests was found in 22% of all cases, including 58% of smear-positive patients, 32% of smear-negative, culture-positive patients, and 0.7% of normal subjects.

Antigens, Bacterial↗
PubMed1989

Slide culture sensitivity tests.

A new method for slide culture sensitivity tests of Mycobacterium tuberculosis is described in which smear-positive sputum spread on slides is incubated without prior decontamination in a selective lysed human blood medium. Results are available 7 days after setting up the tests and are particularly useful for guiding the treatment of smear-positive patients with a long history of unsuccessful chemotherapy. Drug concentrations and definitions of resistance are suggested for tests against isoniazid, streptomycin, PAS, rifampicin ethambutol and ethionamide. A good correlation was seen between the results of these tests and those of standard indirect sensitivity tests.

Antitubercular Agents↗
PubMed1989

Activity and penetration of antituberculosis drugs in mouse peritoneal macrophages infected with Mycobacterium microti OV254.

The activities of some commonly used antituberculosis drugs were investigated within unstimulated peritoneal macrophages and in 7H-9 medium without Tween 80 using Mycobacterium microti OV254 as the target organism. In macrophage cultures, serial concentrations of isoniazid, rifampin, pyrazinamide, or streptomycin were added after a 2.5-h phagocytosis period. Viable counts were carried out at daily intervals for 5 or 6 days. The patterns of susceptibility to the four drugs were similar for M. microti and Mycobacterium tuberculosis. To ensure comparability with daily drug replacements in the macrophage experiments, the period of exposure to drugs in 7H-9 medium was kept to only 3 days. With in vitro culture at pH 6.4, drug penetration, measured as the ratio of MICs in macrophages to MICs in 7H-9 medium, was approximately 5 for isoniazid, 5 for rifampin, and 10 for streptomycin. With in vitro culture at pH 7.4, drug penetration was 100 for streptomycin, and at pH 5.6 it was 1 for pyrazinamide. Pyrazinamide was only bacteriostatic in macrophages but weakly bactericidal during the first day of exposure in vitro.

Animals↗
PubMed1989

Influence of BCG-induced immunity on the bactericidal activity of isoniazid and rifampicin in experimental tuberculosis of the mouse and guinea-pig.

The influence of previous BCG vaccination on the bactericidal activity of isoniazid and rifampicin has been studied using serial counts of viable tubercle bacilli in the spleens and lungs of mice and guinea-pigs infected intravenously with M. tuberculosis, strain H37Rv. In mice, BCG vaccination decreased the bactericidal activity of isoniazid in the spleen, but did not affect its activity in the lungs, where immunity is less strongly expressed. BCG did not influence the bactericidal activity of rifampicin in either organ. In contrast, previous BCG vaccination in the guinea-pig increased the bactericidal activity of isoniazid and rifampicin in the spleen and lungs. The differences between the animal species might result from the immune response being mainly bacteriostatic in the mouse but bactericidal in the guinea-pig.

Animals↗
PubMed1989

The 45 kilodalton molecule of Mycobacterium tuberculosis identified by immunoblotting and monoclonal antibodies as antigenic in patients with tuberculosis.

The object of this study was to discover new M. tuberculosis antigens which are recognized by patients with tuberculosis, because effective serodiagnostic tests are likely to require combinations of different antigens. In our early experiments using immunoblotting, the findings suggested that human sera from smear-negative tuberculosis patients bound to an antigen in the 45 kDa region. Subsequently, estimates of molecular weight in the immunoblots confirmed that the murine monoclonal antibody (MAB) HGT-6 and sera from patients both recognized the same 45 kDa molecule. An antibody-antibody competition assay between MAB HGT-6 and sera from smear-positive tuberculosis patients yielded a positive result in 23 out of 43 sera from patients, but in only four out of 23 from controls. This is further evidence that the 45 kDa antigen is recognized by tuberculous patients. We analysed whether a combination of the 45 kDa antigen results and those of known antigens might better discriminate between minimal smear-negative disease and healthy controls than could test with single antigens. There is no clinically useful laboratory test for smear-negative tuberculosis. In immunoblotting, combining the results with the 65, 45, 38 and 10 kDa antigens gave the best discrimination. This suggests that future serodiagnostic tests for minimal disease, such as the antibody-antibody competition assay, should contain a MAB against the 45 kDa antigen and possibly also against the 10 kDa antigen.

Antibodies, Monoclonal↗
PubMed1988

Controlled clinical trial of complete open surgical drainage and of prednisolone in treatment of tuberculous pericardial effusion in Transkei.

240 patients with active tuberculous pericardial effusion received a 4-drug daily antituberculosis regimen for 6 months and have been studied for 24 months or longer. Those willing were randomly allocated to open pericardial biopsy and complete drainage of pericardial fluid on admission or percutaneous pericardiocentesis as required. All patients were randomly allocated to prednisolone or matching placebo for the first 11 weeks, on a double-blind basis. Complete open drainage on admission abolished the need for pericardiocentesis (p less than 0.01) but did not influence the need for pericardiectomy for subsequent constriction or the risk of death. Among patients who did not have open drainage on admission, 2 (3%) of 76 given prednisolone compared with 10 (14%) of 74 given placebo died of pericarditis (p less than 0.05), 6 (8%) and 9 (12%) respectively required pericardiectomy, 7 (9%) and 17 (23%) repeat pericardiocentesis (p less than 0.05), and 3 (4%) and 7 (9%) open surgical drainage. By 24 months, apart from the 16 who died from pericarditis, all but 3 patients (2%) had a favourable status.

Adolescent↗
PubMed1988

HLA typing in the Hong Kong Chest Service/British Medical Research Council study of factors associated with the breakdown to active tuberculosis of inactive pulmonary lesions.

As part of a multifactorial study of the causes of breakdown to active tuberculosis of inactive pulmonary lesions, HLA-A, -B, and -DR typing was performed on 256 Hong Kong Chinese patients and 100 healthy control subjects. Patients were classified into those with smear-positive, active pulmonary tuberculosis (n = 103), those with inactive disease (n = 113), and those with breakdown to active disease after 6 months or more of inactivity (n = 40). Separately, 21 multiple-case families comprising 38 available parents and 93 offspring were examined for HLA haplotype segregation in relation to infection. Results of both studies indicate that among Hong Kong Chinese there is no statistically significant association between HLA and susceptibility to pulmonary tuberculosis.

Adolescent↗
PubMed1988

Demonstration of increased anti-mycobacterial activity in peripheral blood monocytes after BCG vaccination in British school children.

A blood sample was taken from children aged 13-15 years immediately before BCG vaccination and 8 weeks after. The children were tuberculin skin-test negative to PPD-S before vaccination and positive after. Mononuclear cells were separated from the blood, infected with Mycobacterium microti at a low bacterium/monocyte ratio and allowed to form monolayers in microtitre wells. The infected monolayers were rinsed daily and the change in number of live bacteria in monolayers and supernatants was monitored by colony counts on agar. The cells were bacteriostatic during the first day, thereafter growth accelerated in pre-vaccination monolayers. When monolayers received pulsed exposures to autologous lymphocytes that had been incubated with whole dead tubercle bacilli the growth rates of M. microti were increased. However, growth rates in lymphocyte-pulsed monolayers were significantly lower after vaccination than before. It is proposed that this difference reflects the protective effect of vaccination.

Adolescent↗
PubMed1987

In vitro properties of rifapentine (MDL473) relevant to its use in intermittent chemotherapy of tuberculosis.

In a comparison of in vitro properties of rifapentine (RIF) and rifampicin (RMP), the minimal inhibitory concentration of RIF against Mycobacterium tuberculosis in Tween-albumin liquid medium was usually 0.02 micrograms/ml, 2-3 times lower than for RMP; the bactericidal activity against a log phase culture was slightly less than that of RMP and the recovery after pulsed exposures to 1 microgram/ml of RIF or RMP lasting 6, 24 and 96 h was identical for the two rifamycins. These findings are used to interpret published data from the chronic experimental murine tuberculosis model and support the view that in the mouse, the efficacy of RIF in widely spaced intermittent chemotherapy is the result of its long half-life.

Animals↗
PubMed1987

In vitro activity of new rifamycins against rifampicin-resistant M. tuberculosis and MAIS-complex mycobacteria.

Comparisons were made of the in vitro activity of rifampicin, and the rifamycin derivatives, rifapentine, rifabutin, CGP 29861, CGP 7040 and CGP 27557, against rifampicin-sensitive and rifampicin-resistant strains of Mycobacterium tuberculosis and against the Mycobacterium avium/intracellulare/scrofulaceum (MAIS) complex. The new rifamycins had MICs four to eight times lower than those of rifampicin against sensitive M. tuberculosis strains. Of the 35 rifampicin-resistant strains of M. tuberculosis, 31% were sensitive to rifabutin but only 3-11% to the other rifamycins. The proportions of the MAIS strains found to be sensitive were 35% for rifampicin, 50-60% for CGP 27557, rifapentine and rifabutin and 85-92% for CGP 29861 and CGP 7040.

Antitubercular Agents↗