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Antimicrobial Agents and Chemotherapy, March 1999, p. 537-542, Vol. 43, No. 3
Department of Molecular Microbiology and
Immunology, School of Hygiene and Public Health, Johns Hopkins
University, Baltimore, Maryland 21205
Received 9 February 1998/Returned for modification 9 April
1998/Accepted 14 December 1998
Pyrazinamide (PZA), an analog of nicotinamide, is a prodrug that
requires conversion to the bactericidal compound pyrazinoic acid (POA)
by the bacterial pyrazinamidase (PZase) activity of nicotinamidase to
show activity against Mycobacterium tuberculosis. Mutations
leading to a loss of PZase activity cause PZA resistance in M. tuberculosis. M. kansasii is naturally resistant to PZA and has
reduced PZase activity along with an apparently
detectable nicotinamidase activity. The role of the reduction in PZase
activity in the natural PZA resistance of M. kansasii
is unknown. The MICs of PZA and POA for M. kansasii
were determined to be 500 and 125 µg/ml, respectively. Using
[14C]PZA and [14C]nicotinamide, we
found that M. kansasii had about 5-fold-less PZase activity and about 25-fold-less nicotinamidase activity than
M. tuberculosis. The M. kansasii
pncA gene was cloned on a 1.8-kb
BamHI DNA fragment, using M. avium pncA
probe. Sequence analysis showed that the M. kansasii pncA gene encoded a protein with homology to
its counterparts from M. tuberculosis (69.9%), M. avium (65.6%), and Escherichia coli
(28.5%). Transformation of naturally PZA-resistant M. bovis BCG with M. kansasii pncA conferred
partial PZA susceptibility. Transformation of M. kansasii with M. avium pncA caused functional
expression of PZase and high-level susceptibility to PZA, indicating
that the natural PZA resistance in M. kansasii results
from a reduced PZase activity. Like M. tuberculosis,
M. kansasii accumulated POA in the cells at an acidic pH; however, due to its highly active POA efflux pump, the naturally PZA-resistant species M. smegmatis did not. These
findings suggest the existence of a weak POA efflux mechanism in
M. kansasii.
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Reduced Pyrazinamidase Activity and the Natural
Resistance of Mycobacterium kansasii to the
Antituberculosis Drug Pyrazinamide
*
Corresponding author. Mailing address: Department of
Molecular Microbiology and Immunology, School of Hygiene and Public
Health, Johns Hopkins University, 615 N. Wolfe St., Baltimore, MD
21205. Phone: (410) 614-2975. Fax: (410) 955-0105. E-mail:
yzhang{at}jhsph.edu.
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