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J. Bacteriol., Aug 1996, 4822-4829, Vol 178, No. 16
PS Hoffman, A Goodwin, J Johnsen, K Magee and SJ Veldhuyzen van Zanten
In this study, we compared metronidazole (Mtz)-sensitive and -resistant
strains of Helicobacter pylori for metabolic differences that might
correlate with drug resistance. Included in this study was an isogenic
Mtz(r) strain, HP1107, that was constructed by transforming genomic DNA
from Mtz(r) strain HP439 into Mtz(s) strain HP500. Enzyme activities were
also measured for Mtz(r) strains grown in the presence or absence of 18
micrograms of metronidazole per ml (ca. one-half of the MIC). These studies
confirmed the presence of the Embden-Meyerhof-Parnas, Entner-Doudoroff, and
pentose pathways. H. pylori strains expressed enzymatic activities
indicative of a complete and active Krebs cycle. All strains expressed
pyruvate oxidoreductase (POR) and alpha- ketoglutarate oxidoreductase (KOR)
as measured with the redox-active dye benzyl viologen (30 to 96 nmol/min/mg
of protein for POR and 30 nmol/min/mg of protein for KOR). When grown in
the presence of Mtz at > or = 3.5 micrograms/ml, Mtz(r) strains
expressed no detectable POR or KOR activity. The apparent repression of POR
and KOR activities by Mtz affected bacterial growth as manifest by extended
lag periods and growth yield reductions of > 30%. A dose-dependent
relationship was demonstrated between the metronidazole concentration in
the growth medium and the specific activity of POR measured in bacterial
cell extracts. The observed repression was not due to inactivation of POR
by Mtz. In addition to repression of POR and KOR activities, growth in the
presence of Mtz also led to decreases in the activities of various Krebs
cycle enzymes, including aconitase, isocitrate dehydrogenase and succinate
dehydrogenase. All of the Mtz(r) strains examined expressed isocitrate
lyase and malate synthase activities indicative of the glyoxylate bypass.
No isocitrate lyase activity was detected in Mtz(s) strain HP500.
Isocitrate lyase activity was expressed by HP500 following transformation
to Mtz resistance (Mtz(r) strain HP1107) with DNA from an Mtz(r) strain.
The results of this study suggest that Mtz resistance may be a recessive
trait, possibly involving inactivation of a regulatory gene, that results
in constitutive expression of isocitrate lyase. Repression of POR and KOR
activities in response to low levels of Mtz may be a general response of H.
pylori strains to Mtz, but only resistant strains manage to survive via
activation of compensatory metabolic pathways.
Copyright © 1996, American Society for Microbiology
Metabolic activities of metronidazole-sensitive and -resistant strains of Helicobacter pylori: repression of pyruvate oxidoreductase and expression of isocitrate lyase activity correlate with resistance
Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada. PHOFFMAN@S.DAL.CA
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