130 Trend of First-Line and Second-Line Eradication Therapy for Helicobacter pylori Infection in Korea

Abstract

G A A b st ra ct s to yield these reduction products that are directly toxic to the bacterium. Although mutational inactivation of the rdxA gene is strongly associated with the development of resistance to MNZ, a number of MNZ-resistant strains have also been reported that show no evident change in the rdxA gene (Aliment. Pharmacol. Ther. 24:81-87, 2006), suggesting the potential existence of other mechanisms of resistance. We assumed that these resistant strains exhibit enhanced ability to defend themselves against superoxide radicals by overexpressing bacterial superoxide dismutase (SodB). The present study was designed to examine the expression of sodB and the function of the ferric uptake regulator (Fur) that acts as a transcriptional repressor protein exhibiting iron-dependent binding to the sodB promoter. Methods. H. pylori strain ATCC 700392 was used as the MNZ-susceptible strain and the MNZ-resistant strains used for the study (KS0033, KS0048 and KS0145) were isolated from patients at Keio University Hospital. The expression of sodB under exposure to MNZ was measured by quantitative RT-PCR, and the levels in the susceptible strain and resistant strains were compared. The complete fur of resistant strains was amplified by PCR, cloned into the pCR2.1-TOPO vector, and then sequenced. The Fur proteins were aligned using Genetyx and the protein structures were modeled using Swiss-Model and DeepView-SwisspdbViewer. Results.While sodB expression was scarcely induced by MNZ in ATCC 700392, overexpression of sodB by about 1.7, 2.6 and 2.1-fold was observed in KS0033, KS0048 and KS0145, respectively, under MNZ exposure. Thus, these MNZ-resistant strains showed enhanced sodB expression, as compared with that in ATCC 700392, under exposure to MNZ. The MNZ-resistant strains had a mutant-type of Fur protein, in which Asn 118 was replaced by His (N118H). From the results of the homologymodeling, Asn 118 was predicted to be located in the 5th alpha-helix region that projected outward. It is conceivable that the N118H of Fur affected the affinity of Fur for iron or the sodB promoter region, resulting in sodB overexpression. Conclusion. Fur mutation in H. pylori, resulting in substitution of Asn 118 by His, is associated with the development of resistance to MNZ.