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Biomedical subjects

D A Mitchison

Publications and source records attributed to D A Mitchison.

At least 37 records · Page 2Linked to original sources
PubMed1998

Protein synthesis is shutdown in dormant Mycobacterium tuberculosis and is reversed by oxygen or heat shock.

Oxygen-limiting conditions are critical to the survival of the bacteria in tuberculosis. Mycobacterium tuberculosis can survive anaerobiosis in vitro for long periods of time only after a gradual transition to a microaerophilic stationary phase. The underlying mechanism behind stationary phase adaption needs to be elucidated. The protein profiles of Mycobacterium tuberculosis during long-term stationary phase growth and under strict anaerobic incubation were monitored by [35S]methionine labelling, SDS-PAGE and fluorography. These experiments have established that protein synthesis gradually decreased over 50 days in the long-term stationary phase cultures which were considered to be microaerophilic. There was an 80% linear decrease in the level of total protein synthesis during the first 40 days of microaerophilic growth and then the rate of protein synthesis faded quickly. For the first time we have shown that total protein synthesis shutdown occurred when bacilli were incubated under further anaerobic conditions. Viability, estimated by cfu counts, remained constant during stationary phase growth and under anaerobic incubation. Furthermore, when oxygen was introduced into the anaerobic culture, protein synthesis restarted. Also heat shock at 45 degrees C, 48 degrees C and 50 degrees C rapidly induced protein synthesis in stationary and anaerobic cultures. These data indicate that dormant bacteria shut down protein synthesis but remain responsive to specific stimuli which restore protein synthesis. In addition the dormant bacilli induced by anaerobiosis developed more heat resistance than nondormant organisms.

Anaerobiosis↗
PubMed1998

Rifapentine and isoniazid in the continuation phase of treating pulmonary tuberculosis. Initial report.

A randomized comparison has been made of three times weekly rifampin plus isoniazid (HR3) with rifapentine plus isoniazid given once weekly (HRp1) or on 2 of 3 wk (HRp1.2/3) in the continuation phase of 6-mo regimens (each starting with an initial 2 mo of 4-drug therapy) for the treatment of pulmonary tuberculosis in 672 Chinese patients in Hong Kong. Because of poor bioavailability of the rifapentine used (produced in China), its dose size was increased from 600 mg initially to about 750 mg in the last third of patients to obtain serum concentrations similar to those with rifapentine of Western origin; all doses were given after a meal promoting absorption. After initial exclusions, an intent to treat analysis, done on the remaining 592 patients, showed 45 adverse treatment events in 7 of 190 HR3 patients, in 17 of 199 HRp1 patients, and in 21 of 203 HRp1.2/3 patients; of these, 42 were bacteriological or radiographic relapses after the end of treatment (HR3 versus HRp1, p = 0.04; HR3 versus HRp1.2/3, p = 0.01). Patients with organisms initially sensitive or resistant to isoniazid or streptomycin had similar relapse rates. The high relapse rate in the HRp1 regimen suggests that the rifapentine dose should be increased. Similarity of relapse rates, 8.9% and 10.4%, after the HRp1 and HRp1.2/3 regimens, respectively, indicates that irregularity in taking rifapentine/isoniazid could be tolerated. The few adverse side effects in the continuation phase in the rifapentine regimens were less frequent than in the HR3 regimen.

Adolescent↗
PubMed1998

How drug resistance emerges as a result of poor compliance during short course chemotherapy for tuberculosis.

OBJECTIVE: To explore mechanisms by which drug resistance might arise as a result of poor compliance during short course chemotherapy. DESIGN: Four theoretical mechanisms are first described. RESULTS: Examples of the way the mechanisms probably operate are taken from: 1) a study of once-weekly chemotherapy with streptomycin and isoniazid, and 2) the pattern of drug susceptibility in cultures from patients who relapsed after the end of treatment. CONCLUSION: Good compliance is vitally important. The value of a fourth drug in the initial phase of chemotherapy in preventing resistance is questioned. An explanation for mono-resistance to rifampicin in patients with the acquired immune deficiency syndrome (AIDS) is suggested.

AIDS-Related Opportunistic Infections↗
PubMed1998

Metronidazole has no antibacterial effect in Cornell model murine tuberculosis.

SETTING: Experiments in vitro on the bactericidal activity of metronidazole and in the Cornell model of murine tuberculosis. OBJECTIVE: To assess the sterilising activity of maximal metronidazole dosage and its activity against bacilli held dormant by immunity in the mouse. DESIGN: In vitro experiments showed that metronidazole was only bactericidal at attainable concentrations (50-100 microg/ml) under anaerobic conditions. In the Cornell model, isoniazid 25 mg/kg and high dosage pyrazinamide 1000 mg/kg was given in the diet with and without 1500 mg/kg metronidazole for the initial 14 weeks of sterilising chemotherapy. In the subsequent sterile state, metronidazole at 0, 100 and 250 mg/kg was given by daily gavage for 6 weeks. Finally, the mice were given 3 weeks of high dosage steroids and their organs were cultured in selective liquid medium. RESULTS: Metronidazole had no activity either in the initial sterilising phase or in the subsequent sterile state. CONCLUSION: The O2 tension in the cellular lesions of murine tuberculosis is unlikely to be sufficiently low to allow metronidazole to act. Its activity should be assessed in caseous lesions.

Animals↗
PubMed1998

The origins of DOT.

Explore the source record for details and available documents.

Antitubercular Agents↗
PubMed1997

An effective method of RNA extraction from bacteria refractory to disruption, including mycobacteria.

A high yield, rapid and simple procedure is described for extracting RNA from mycobacteria and other micro-organisms refractory to disruption. The method yielded 20 microg RNA/109 Mycobacterium bovis BCG, more than 10 times greater than our previous method. Intact full length hsp 70 (dnaK) mRNA was detected by northern blotting and quantitated after heat shock by slot blot hybridisation.

Base Sequence↗
PubMed1997

The early bactericidal activity of isoniazid related to its dose size in pulmonary tuberculosis.

Collections of sputum from 105 patients with newly diagnosed pulmonary tuberculosis were made before and at 1 and 2 d after the start of chemotherapy with isoniazid (INH) alone given to groups of patients in doses of 600 mg, 300 mg, 150 mg, 75 mg, 37.5 mg, 18.75 mg, and 9 mg daily, as well as from an untreated group. Counts of colony forming units (cfu) of Mycobacterium tuberculosis in the collections were set up on plates of selective 7H10 medium. The early bactericidal activity (EBA) of INH was defined as the decrease in log10 cfu/ml sputum/day during the first 2 d of treatment. A smooth curve relating EBA to log dose was obtained, with 600 mg INH yielding the highest mean EBA of 0.539, and 18.75 mg INH yielding the lowest EBA (0.111) that could be distinguished from the bactericidal activity of the untreated group. The ratio of the usual dose of 300 mg INH to the lowest dose, of 18.75 mg, that produced a detectable EBA, termed the therapeutic margin, was therefore 16, in contrast to the lower therapeutic margin of 4 for rifampin. The EBA was related to the INH acetylator genotype of patients treated with 600 mg or 9 mg INH.

Acetylation↗
PubMed1997

The early bactericidal activity of ciprofloxacin in patients with pulmonary tuberculosis.

The early bactericidal activity (EBA) of ciprofloxacin (CIP) was measured in 80 patients with previously untreated, smear-positive pulmonary tuberculosis by counting viable bacilli in sputum collections during the first 2 d of treatment. Groups of about 10 patients were treated daily with graded doses of CIP or with 300 mg isoniazid or with no drug. The mean EBA, defined as the fall in log CFU/ ml sputum/d, increased from -0.011 in the no drug group to 0.046, 0.092, 0.121, and 0.205 in the groups receiving 250, 500, 1,000, or 1,500 mg CIP, respectively, a highly significant trend. These results demonstrate the antimycobacterial activity of CIP in high dosage, though the mean EBAs of 0.55 and 0.66 in two groups receiving isoniazid were much higher.

Adult↗
PubMed1997

Bioavailability of Chinese rifapentine during a clinical trial in Hong Kong.

SETTING: A clinical trial of rifapentine in Hong Kong. OBJECTIVE: Assessment of the bioavailability of the Chinese rifapentine used in the trial. DESIGN: The content of rifapentine in serum samples taken from 287 patients during the administration of four batches of the drug was measured by microbiological assay. RESULTS: An initial comparison of areas under curve obtained in a random allocation to 40 patients of rifapentine either of Western or Chinese origin indicated that the bioavailability of the Chinese drug was 74% of the Western drug. The bioavailability of the second batch was found to be about 66% of the Western drug. The dose of the last two batches of rifapentine was therefore increased from the planned 600 mg to 750 mg, or briefly to 900 mg; serum concentrations were then similar to those obtained with the Western drug. Bioavailability did not change during the use of each drug batch. CONCLUSION: A comparison of the results obtained in the trial with the initial two batches and the final batches will estimate the effects of rifapentine dose size on its efficacy and toxicity.

Adult↗
PubMed1996

Bactericidal action of ofloxacin, sulbactam-ampicillin, rifampin, and isoniazid on logarithmic- and stationary-phase cultures of Mycobacterium tuberculosis.

The bactericidal actions of ofloxacin and sulbactam-ampicillin, alone and in combination with rifampin and isoniazid, on exponential-phase and stationary-phase cultures of a drug-susceptible isolate of Mycobacterium tuberculosis were studied in vitro. In exponential-phase cultures, all drugs were bactericidal, with the higher concentrations of ofloxacin (5 micrograms/ml) and sulbactam-ampicillin (15 micrograms of ampicillin per ml) being as bactericidal as 1 microgram of isoniazid per ml or 1 microgram of rifampin per ml. In two-drug combinations, both drugs increased the levels of activity of isoniazid and rifampin and were almost as bactericidal as isoniazid-rifampin; they also appeared to increase the level of activity of isoniazid-rifampin in three-drug combinations. In contrast, ofloxacin and sulbactam-ampicillin had little bactericidal activity against stationary-phase cultures and were less active than isoniazid or rifampin alone. Furthermore, in two-drug or three-drug combinations, they did not increase the level of activity of isoniazid, rifampin, or isoniazid-rifampin. These findings suggest that ofloxacin and sulbactam-ampicillin are likely to be most useful in the early stages of treatment and in preventing the emergence of resistance to other drugs but are unlikely to be effective as sterilizing drugs helping to kill persisting lesional bacilli.

Ampicillin↗
PubMed1996

Preventive chemotherapy of tuberculosis in Cornell model mice with combinations of rifampin, isoniazid, and pyrazinamide.

The efficacies of rifampin-containing preventive regimens were measured in Cornell model mice in which an initially severe infection with Mycobacterium tuberculosis H37Rv was first treated for 7 weeks with 25 mg of isoniazid and 1,000 mg of pyrazinamide per kg of body weight in the diet and then with one of four test regimens given by daily oral gavage for 6 weeks. These regimens were 15 mg of rifampin per kg alone (R), rifampin plus 25 mg of isoniazid per kg (RH), rifampin plus 150 mg of pyrazinamide per kg (RZ), or rifampin plus isoniazid and pyrazinamide (RHZ). The interval between the rifampin gavage and the gavage with the other drugs ranged from 10 to 45 min, so that interference with rifampin absorption did not occur. Mice were sacrificed at 11 and 20 weeks after the termination of chemotherapy, with each killing being preceded by 3 weeks of high-dose dihydrocortisone treatment. Entire spleens and lungs were cultured. The proportions of mice with positive spleens at either killing time were 74% of 43 mice treated with R, 63% of 41 mice treated with RH, 65% of 43 mice treated with RZ, and 53% of 45 mice treated with RHZ, a just significant (P = 0.04) trend for fewer positive spleens with increasing numbers of drugs in the regimen. However, no trend was found in the corresponding proportions of mice with positive spleens or lungs, which were 81, 63, 65, and 71% for mice treated with R, RH, RZ, and RHZ, respectively. Thus, in the Cornell model, R alone, RH, RZ, and RHZ all had similar efficacies.

Animals↗
PubMed1996

Early bactericidal activity of ethambutol, pyrazinamide and the fixed combination of isoniazid, rifampicin and pyrazinamide (Rifater) in patients with pulmonary tuberculosis.

The early bactericidal activity (EBA) of ethambutol, pyrazinamide and the fixed combination of isoniazid, rifampicin and pyrazinamide (Rifater: Mer National) was evaluated in patients with pulmonary tuberculosis who were sputum-positive on microscopy for acid-fast bacilli. Twenty-eight patients (mean age 33 years and weight 51 kg on average; range 40-59 kg) were studied. The fall in viable counts of Mycobacterium tuberculosis in sputum collections during the 2 days following the start of treatment was estimated from counts of colony-forming units (CFUs) of M. tuberculosis per ml of sputum cultured on selective 7H10 agar medium. The EBA for ethambutol determined in 9 patients was 0.245 +/- 0.046, log10 CFU/ml sputum/day, that for pyrazinamide was 0.003 +/- 0.014 log10 CFU/ml sputum/day and that for Rifater 0.558 +/- 0.054 log10 CFU/ml sputum/day. The results obtained are similar to those reported in a previous study of the first 2 days of treatment, but in smaller numbers of patients, and confirm the moderate EBA of ethambutol while pyrazinamide is again shown to have very little EBA. Rifater has a marked EBA which may be due mainly to the action of isoniazid. This methodology may be valuable in the rapid evaluation of the bactericidal activity of new antituberculosis agents and the comparison of different dose sizes of agents of the same class.

Adolescent↗
PubMed1995

The bacterial DNA content of mouse organs in the Cornell model of dormant tuberculosis.

SETTING: The Cornell model of murine tuberculosis has proved useful for demonstrating and studying dormancy. However, it has not previously been used to investigate the molecular aspects of dormancy. OBJECTIVE: To obtain a profile of the amount of Mycobacterium tuberculosis DNA at various stages of the Cornell model. DESIGN: BALB/C mice were infected intravenously with 2.7 x 10(6) cfu M tuberculosis strain H37Rv; they were left for two weeks, treated for 14 weeks with isoniazid and pyrazinamide and left untreated for a further 14 weeks. Spleens and lungs at start of treatment and at 8, 12, 14, 18, 24 and 28 weeks thereafter were examined by culture, and DNA in tissue homogenates was quantitated by polymerase chain reaction (PCR) and dot blot hybridisation. RESULTS: Culture and quantitative PCR estimated initial bacillary content at about 10(7) per organ. Thereafter, organ cultures rapidly declined and were usually negative between 14 and 28 weeks. However, during this period quantitative PCR consistently estimated about 5.5 log10 bacilli equivalents in spleens and lungs. Dot blot hybridisation sensitive to about 10 ng bacillary DNA was usually positive pretreatment and occasionally during and after treatment, hence confirming the PCR results. CONCLUSIONS: There is persistence of significant quantities of M. tuberculosis DNA throughout the various stages of the model. This may represent dead bacilli, free DNA or dormant forms.

Animals↗