Comparison of the characteristics of Mycobacterium tuberculosis isolates from sputum and lung lesions in chronic tuberculosis patients.

Mycobacterium tuberculosis (Mtb) in sputum originates from lung cavities in tuberculosis (TB) patients. But drug susceptibility testing (DST) of sputum Mtb can not be conducted the same as in the lung because mutagenesis of bacilli may be happening in the lung during treatment and result in the possibility of the presence of heterogeneous drug-resistant subpopulations in the different lung lesions. This could be one of the reasons for low cure rates for multi-drug resistant (MDR)-TB. We studied the resected lungs of nine surgery patients with chronic TB. The isolates isolated from the sputum and different lung lesions of each patient were tested for phenotypic DST and genotyped using restriction fragment length polymorphism (RFLP) typing method. Genetic analysis to resistance to first and second line drugs was also performed. Five of nine patients were MDR-TB and three XDR-TB. DST results for ten anti-TB drugs were in accordance among different lung lesions in eight patients. However, only three of these eight patients showed the concordance of DST with sputum. Even though the isolates were heteroresistant, genotyping them by RFLP showed the clonal population in each individual patient. Six of eight followed-up patients achieved successful cure. In conclusion, the heteroresistance between sputum and lung lesions and a clonal population without mixed infection might provide useful information in establishing treatment regimen and surgery decision for MDR- and XDR-TB.

Patterns of pncA mutations in drug-resistant Mycobacterium tuberculosis isolated from patients in South Korea.

BACKGROUND: Pyrazinamide (PZA), one of the most effective anti-tuberculosis drugs, becomes toxic to Mycobacterium tuberculosis when converted to pyrazinoic acid by pyrazinamidase (PZase). PZA resistance is caused mainly by the loss of enzyme activity by mutation. OBJECTIVE: To investigate the patterns of pncA mutations in PZA-resistant mycobacteria isolated from South Korean patients. METHODS: Mycobacterial isolates with clinically proven drug resistance were cultured to determine susceptibility to anti-tuberculosis agents. pncA mutations were recognised by sequencing and compared with the relevant wild-type DNA sequence. RESULTS: Among 108 isolates, 102 were successfully cultured and underwent drug susceptibility testing; all were multidrug-resistant (MDR). pncA mutations were found in 86 cultured isolates (85.1%): 55 (84.6%) in MDR and 31 (86.1%) in extensively drug-resistant isolates. Substitution of a single nucleotide was most common. The most frequent mutations were a deletion that caused a frameshift at nucleotide (nt) 71, a substitution at nt 403 and a substitution at nt 11. Combined, these accounted for ≈ 40% of all mutations. However, 15 samples (14.9%) with defective PZase activity showed no mutation. CONCLUSION: pncA mutation in M. tuberculosis is a major mechanism of PZA resistance in MDR isolates from patients in South Korea. The patterns of mutation might be more scattered and diverse. DNA-based diagnosis of PZA resistance has potential for the rapid detection of drug resistance.

Assessment of vitamin B-6 status in young women consuming a controlled diet containing four levels of vitamin B-6 provides an estimated average requirement and recommended dietary allowance.

The Recommended Dietary Allowance (RDA) of vitamin B-6 for young women was recently reduced from 1.6 to 1.3 mg/d based on an adequate plasma pyridoxal phosphate (PLP) concentration of 20 nmol/L. To assess vitamin B-6 requirements and suggest recommendations for intake, seven healthy young women consumed a controlled diet providing 1.2 g protein/kg body weight for a 7-d adjustment period (1.0 mg vitamin B-6/d) and three successive 14-d experimental periods (1.5, 2.1 and 2.7 mg/d, respectively). Direct and indirect vitamin B-6 status indicators were measured in plasma, erythrocytes and urine. Indicators most strongly correlated with vitamin B-6 intake [i.e., plasma and erythrocyte PLP, urinary 4-pyridoxic acid (4-PA) and total vitamin B-6] were regressed on vitamin B-6 intake and the dietary vitamin B-6 to protein ratio. Inverse prediction using adequate and baseline values estimated vitamin B-6 requirement. Adequate values were determined for plasma PLP and urinary 4-PA from baseline values of 60 previous subjects, using the statistical method suggested by Sauberlich. The current study suggests a vitamin B-6 Estimated Average Requirement (EAR) for young women of 1.1 mg/d or 0.016 mg/g protein, and a RDA of 1.5 mg/d or 0.020 mg/g protein. When results from this study are combined with data from four other recent studies, the combined data predict an EAR of 1.2 mg/d or 0.015 mg/g protein, and a RDA of 1.7 mg/d or 0.018 mg/g protein. This study suggests that the current vitamin B-6 RDA may not be adequate.