Affiliation:
1. Department of Molecular Microbiology and Immunology, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland 21205
Abstract
ABSTRACT
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 [
14
C]PZA and [
14
C]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
Bam
HI 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
.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
46 articles.
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