Use this URL to cite or link to this record in EThOS:
Title: Investigation into mycobacterial persistence and early markers of outcome in the treatment of pulmonary tuberculosis
Author: Sloan, Derek
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2013
Availability of Full Text:
Access from EThOS:
Access from Institution:
Background: Development of ultra-short chemotherapy for tuberculosis (TB) is thwarted by drug-tolerant bacillary persistence and a lack of surrogate endpoints to predict outcome from early clinical studies. Characterising bacillary elimination amongst TB patients may provide important new information. Bacilli harbouring intra-cytoplasmic lipid bodies (LBs) may represent a drug-tolerant phenotype, responsible for delayed bacterial clearance. Methods: Malawian adults with pulmonary TB were treated with standard 6 month therapy. Two quantitative sputum culture methods were used to model bacillary elimination during the first 2 months; serial sputum colony counting (SSCC) and time to positivity (TTP) in BACTEC MGIT broth. Fluorescence microscopy was used to assess the proportion of LB positive bacilli on sputum smears. Plasma concentrations of anti-TB drugs were assayed at day 14 or 21. Patients were followed until one year post-treatment. Outcomes were defined as favourable (stable cure) or unfavourable (failure/relapse). The effect of microbiological and pharmacological factors on outcome was assessed. Results: 169 patients (59% with HIV co-infection) were recruited. Of 133 final outcomes, 15 (11%) were unfavourable. Partial likelihood non-linear mixed effects (NLME) modelling of SSCC data from 86 (64%) patients showed biphasic bacillary elimination; slow late-phase eradication of persisters was associated with unfavourable outcome (p=0.001). Linear mixed effects (LME) modelling of TTP data from 124 (93%) patients showed that a slower MGIT Bacillary Elimination Rate (MBER) was associated with unfavourable outcome (p=0.007). 28% (range 0-79%) of acid-fast bacilli in baseline sputum samples were LB positive. During the first month there was a trend towards higher LB counts in patients who went on to have unfavourable vs. favourable outcomes (p=0.085). Low plasma rifampicin and isoniazid concentrations were reported in 87% and 50% patients respectively. A lower isoniazid AUC(0-6hr) exposure was associated with unfavourable outcome (p=0.035). Conclusions: The two main findings were: 1. Modelling of bacillary elimination during the first 2 months of TB therapy predicted long-term outcome. The MBER, in particular, could be calculated for 93% of patients and should be considered as a surrogate marker for early clinical trials. 2. The observation of a higher proportion of LB positive bacilli in later sputum samples from patients with unfavourable outcomes suggests that these may be drug-tolerant persister cells, with negative implications for treatment efficacy.
Supervisor: Davies, Geraint R.; Mwandumba, Henry C.; Khoo, Saye H. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: RB Pathology