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 similar to 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.