Characterisation of the pncA gene in Mycobacterium tuberculosis isolates from Gauteng, South Africa.
METHODS
The use of pyrazinamide (PZA) is important for the treatment of Mycobacterium tuberculosis as it is bactericidal to semi-dormant mycobacteria that are not affected by other drugs. The incidence of resistance to PZA and other drugs used in the treatment of M. tuberculosis is increasing in South Africa.


OBJECTIVE
To characterise the pncA gene of M. tuberculosis isolates from Gauteng, South Africa, and to develop a rapid diagnostic method.


METHODS
The pncA gene and the putative regulatory gene were characterised by sequence analysis in a total of six PZA susceptible and 15 resistant isolates. The association with classical PZA susceptibility testing and PZase activity was determined.


RESULTS
All PZA-resistant isolates were PZase negative as well as resistant to at least one other anti-tuberculosis drugs. Mutations were identified throughout the length of the pncA gene in 10/15 PZA-resistant isolates. Five lacked PZase activity, but the wild type pncA sequence was present. In all six PZase-positive strains, a PZA-susceptible pattern was obtained on BACTEC and the wild type pncA sequence was present.


CONCLUSIONS
Sequencing is an effective means to identify mutations in the pncA gene in M. tuberculosis and therefore resistance to PZA. The fact that some PZA-resistant M. tuberculosis isolates lack mutations in the pncA gene suggests that alternative mechanisms for drug resistance exist. In PZase negative strains with no genetic changes which are resistant to 100 microg/ml and susceptible to 300 microg/ml, 300 microg/ml may be a more reliable breakpoint.
Bishop
K S
KS
Department of Virology, Faculty of Medicine, University of Natal, Durban, KwaZulu-Natal, South Africa.
Blumberg
L
L
Trollip
A P
AP
Smith
A N
AN
Roux
L
L
York
D F
DF
Kiepiela
P
P
D000353:Africa, Southern / Q000453:epidemiology; D000581:Amidohydrolases / Q000235:genetics / Q000302:isolation & purification*; D000995:Antitubercular Agents / Q000627:therapeutic use; D005798:Genes, Bacterial / Q000235:genetics; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000737:chemistry* / Q000235:genetics*; D011718:Pyrazinamide / Q000627:therapeutic use; D018088:Tuberculosis, Multidrug-Resistant / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics
D000995:Antitubercular Agents; D011718:Pyrazinamide; D000581:Amidohydrolases; C022490:pyrazinamide deamidase