Identification of differentially regulated proteins in metronidozole resistant Helicobacter pylori by proteome techniques.

Resistance to metronidazole (MTZ) is common among Helicobacter pylori strains in many societies, and results from loss of function mutations in genes for one or more cellular nitroreductases. When functional, these enzymes convert MTZ from a harmless prodrug to mutagenic and bacteriocidal products (probably hydroxylamine-type compounds), and in the process may generate active reactive oxygen metabolites. Here we examine the protein profiles of a derivative of strain 26695 that is resistant to moderate levels of MTZ because of mutation in rdxA (HP0954), the gene for the most important of these nitroreductases. The strain was grown with and without 18 micrograms/mL of MTZ to assess whether sublethal exposure triggers an adaptive response. Bacterial lysates were subjected to two-dimensional (2-D) electrophoresis and protein bands were identified by mass spectrometry and sequence analysis. Several proteins were decreased at least two-fold during growth with MTZ, yet the levels of various isoforms of alkylhydroperoxide reductase (AHP) (encoded by ahpC HP1563) were increased. AHP is an essential enzyme, and had been linked to resistance to oxygen toxicity in various prokaryotic and eukaryotic systems; we propose that the ability of an rdxA mutant strain to increase AHP abundance during exposure to MTZ is critically important in the realization of the resistance phenotype. More generally, these results highlight the potential of proteome analysis to tracing out how pathogenic bacteria cope with the challenges imposed on them by therapy or host responses to infection.