Frame-shift mutations in NAD(P)H flavin oxidoreductase encoding gene (frxA) from metronidazole resistant Helicobacter pylori ATCC43504 and its involvement in metronidazole resistance

Metronidazole is a critical ingredient for combination therapies of Helicobacter pylori infection, the major cause of peptic ulcer and gastric cancer. It has been recently reported that metronidazole resistance from H. pylori ATCC43504 is caused by the insertion of a mini-IS605 sequence and deletion of sequences in an oxygen insensitive NAD(P)H nitroreductase encoding gene (rdxA). We also found that an additional gene (frxA) encoding NAD(P)H flavin oxidoreductase in the same strain was truncated by frame-shift mutations. To assess whether the frxA truncation is also involved in metronidazole resistance, metronidazole sensitive H. pylori strains ATCC43629 and SS1 were transformed by the truncated frxA gene cloned from strain ATCC43504. All transformed cells grew on agar plates containing 16 microg ml(-1) of metronidazole. The involvement of the frxA gene in metronidazole resistance was also confirmed by insertion inactivation of frxA and/or rdxA genes from strain ATCC43629 and one metronidazole sensitive clinical isolate H. pylori 2600. In addition, the frxA gene cloned from the H. pylori 2600 showed metronidazole nitroreductase activity in Escherichia coli and rendered ordinary metronidazole resistant E. coli to metronidazole sensitive cell. These results indicate that the frxA gene may also be involved in metronidazole resistance among clinical H. pylori isolates.     

Roles of FrxA and RdxA nitroreductases of Helicobacter pylori in susceptibility and resistance to metronidazole

The relative importance of the frxA and rdxA nitroreductase genes of Helicobacter pylori in metronidazole (MTZ) susceptibility and resistance has been controversial. Jeong et al. (J. Bacteriol. 182:5082--5090, 2000) had interpreted that Mtz(s) H. pylori were of two types: type I, requiring only inactivation of rdxA to became resistant, and type II, requiring inactivation of both rdxA and frxA to become resistant; frxA inactivation by itself was not sufficient to confer resistance. In contrast, Kwon et al. (Antimicrob. Agents Chemother. 44:2133--2142, 2000) had interpreted that resistance resulted from inactivation either of frxA or rdxA. These two interpretations were tested here. Resistance was defined as efficient colony formation by single cells from diluted cultures rather than as growth responses of more dense inocula on MTZ-containing medium. Tests of three of Kwon's Mtz(s) strains showed that each was type II, requiring inactivation of both rdxA and frxA to become resistant. In additional tests, derivatives of frxA mutant strains recovered from MTZ-containing medium were found to contain new mutations in rdxA, and frxA inactivation slowed MTZ-induced killing of Mtz(s) strains. Northern blot analyses indicated that frxA mRNA, and perhaps also rdxA mRNA, were more abundant in type II than in type I strains. We conclude that development of MTZ resistance in H. pylori requires inactivation of rdxA alone or of both rdxA and frxA, depending on bacterial genotype, but rarely, if ever, inactivation of frxA alone, and that H. pylori strains differ in regulation of nitroreductase gene expression. We suggest that such regulatory differences may be significant functionally during human infection.     

Sequential inactivation of rdxA (HP0954) and frxA (HP0642) nitroreductase genes causes moderate and high-level metronidazole resistance in Helicobacter pylori

Helicobacter pylori is a human-pathogenic bacterial species that is subdivided geographically, with different genotypes predominating in different parts of the world. Here we test and extend an earlier conclusion that metronidazole (Mtz) resistance is due to mutation in rdxA (HP0954), which encodes a nitroreductase that converts Mtz from prodrug to bactericidal agent. We found that (i) rdxA genes PCR amplified from 50 representative Mtz(r) strains from previously unstudied populations in Asia, South Africa, Europe, and the Americas could, in each case, transform Mtz(s) H. pylori to Mtz(r); (ii) Mtz(r) mutant derivatives of a cultured Mtz(s) strain resulted from mutation in rdxA; and (iii) transformation of Mtz(s) strains with rdxA-null alleles usually resulted in moderate level Mtz resistance (16 microg/ml). However, resistance to higher Mtz levels was common among clinical isolates, a result that implicates at least one additional gene. Expression in Escherichia coli of frxA (HP0642; flavin oxidoreductase), an rdxA paralog, made this normally resistant species Mtz(s), and frxA inactivation enhanced Mtz resistance in rdxA-deficient cells but had little effect on the Mtz susceptibility of rdxA(+) cells. Strains carrying frxA-null and rdxA-null alleles could mutate to even higher resistance, a result implicating one or more additional genes in residual Mtz susceptibility and hyperresistance. We conclude that most Mtz resistance in H. pylori depends on rdxA inactivation, that mutations in frxA can enhance resistance, and that genes that confer Mtz resistance without rdxA inactivation are rare or nonexistent in H. pylori populations.     

Intracellular redox status and antibiotic resistance in enterogastric micro-aerophilic bacteria: evidence for the 'scavenging of oxygen' hypothesis

Metronidazole and glutathione reduction activities were measured in situ in the micro-aerophilic bacteria Campylobacter coli and Helicobacter pylori employing 14N- and 1H-nuclear magnetic resonance spectroscopy. The properties of these enzyme activities were investigated in matched pairs of strains with sensitive and resistant phenotypes to the antimicrobial metronidazole. The results indicated that the ability of each type of strain to reduce metronidazole corresponded to its sensitive or resistance phenotype. Higher levels of glutathione reduction and a significantly lower Ki for metronidazole were observed in sensitive strains compared to resistant strains. These findings suggested a relationship between the cellular machinery regulating intracellular redox status in C. coli and H. pylori, and the effects of metronidazole on these bacteria, which supported the 'scavenging of oxygen' hypothesis.     

The rdxA gene plays a more major role than frxA gene mutation in high-level metronidazole resistance of Helicobacter pylori in Taiwan

BACKGROUND: Metronidazole-resistant H. pylori associating with mutations of rdxA or frxA is still a debated topic. This study investigates whether rdxA and frxA mutations of H. pylori accounted for the high MIC value (>/= 64 micro g/ml) of metronidazole (Mtz). MATERIAL AND METHODS: From 126 clinical H. pylori isolates, we examined 14 Mtz-sensitive, 18 Mtz-resistant H. pylori, and eight pairs of Mtz-sensitive and Mtz-resistant colonies simultaneously present within a single gastric biopsy. The paired strains from one single biopsy were proven identical by PCR-RFLP. MICs of Mtz were checked by the E-test and agar dilution method. The mutations of rdxA and frxA sequencing were matched with the Mtz-susceptible ATCC 26695 and J99. RESULTS: There were 89% (16/18) of Mtz-resistant isolates with mutation of RdxA. Half of the 14 Mtz-sensitive strains, all without mutation of RdxA, still contained truncation of FrxA. Within the paired isolates from a single biopsy, rdxA mutation (86%) was more common than frxA mutation (43%) in those isolates with high-level Mtz-resistant H. pylori. RdxA truncation was more prevalent in Mtz-resistant strains with high MICs than in those with low to moderate MICs (75% vs. 20%, p =.01, OR: 12, 95% CI: 1.8-81.7). CONCLUSION: Mutations in the rdxA gene rather than the frxA gene generally determine a high MIC level of Mtz-resistant H. pylori in Taiwan.     

Analysis of the rdxA gene in high-level metronidazole-resistant clinical isolates confirms a limited use of rdxA mutations as a marker for prediction of metronidazole resistance in Helicobacter pylori

Metronidazole (Mtz) resistance in the gastric pathogen Helicobacter pylori is closely associated with inactivation of the nitroreductase gene rdxA. In order to identify respective mutations for diagnostic purposes we analyzed the rdxA gene in a collection of high-level Mtz-resistant clinical H. pylori isolates. Size alterations in the rdxA gene region were found in only two out of 45 and one out of 40 isolates showing lower-level (minimal inhibitory concentrations (MICs) 32-192 microg ml(-1)) and high-level (MIC>/=256 microg ml(-1)) Mtz resistance, respectively. Point mutations that interrupt the rdxA reading frame were detected in two out of eight high-level resistant isolates (MICs>/=256 microg ml(-1)). Most remarkably, the rdxA gene sequence was found to be identical in four out of five high-level Mtz-resistant and -susceptible paired H. pylori isolates from the same patients each. Taken together, these results demonstrate that although some isolates carry classical resistance-associated rdxA mutations, as described earlier, the use of rdxA mutations as a marker for prediction of Mtz resistance is limited.     

Metronidazole activation is mutagenic and causes DNA fragmentation in Helicobacter pylori and in Escherichia coli containing a cloned H. pylori RdxA(+) (Nitroreductase) gene

Much of the normal high sensitivity of wild-type Helicobacter pylori to metronidazole (Mtz) depends on rdxA (HP0954), a gene encoding a novel nitroreductase that catalyzes the conversion of Mtz from a harmless prodrug to a bactericidal agent. Here we report that levels of Mtz that partially inhibit growth stimulate forward mutation to rifampin resistance in rdxA(+) (Mtz(s)) and also in rdxA (Mtz(r)) H. pylori strains, and that expression of rdxA in Escherichia coli results in equivalent Mtz-induced mutation. A reversion test using defined lac tester strains of E. coli carrying rdxA(+) indicated that CG-to-GC transversions and AT-to-GC transitions are induced more frequently than other base substitutions. Alkaline gel electrophoretic tests showed that Mtz concentrations near or higher than the MIC for growth also caused DNA breakage in H. pylori and in E. coli carrying rdxA(+), suggesting that this damage may account for most of the bactericidal action of Mtz. Coculture of Mtz(s) H. pylori with E. coli (highly resistant to Mtz) in the presence of Mtz did not stimulate forward mutation in E. coli, indicating that the mutagenic and bactericidal products of Mtz metabolism do not diffuse significantly to neighboring (bystander) cells. Our results suggest that the widespread use of Mtz against other pathogens in people chronically infected with H. pylori may stimulate mutation and recombination in H. pylori, thereby speeding host-specific adaptation, the evolution of virulence, and the emergence of resistance against Mtz and other clinically useful antimicrobials.     

Oxidases and reductases are involved in metronidazole sensitivity in Helicobacter pylori

Helicobacter pylori is a contributing factor to the development of gastric and duodenal ulcers and some gastric cancers. Some therapeutic regimes comprise of a number of components, one of which is the antimicrobial metronidazole. A problem with these therapies is the increasing prevalence of metronidazole-resistant (MtrR) H. pylori strains. Several resistance mechanisms have been proposed, and this study addresses the 'scavenging of oxygen' hypothesis. Spectrophotometric assays of cytosolic fractions indicated that metronidazole-sensitive (MtrS) H. pylori isolates had 2.6-fold greater nicotinamide adenine dinucleotide (NADH) oxidase activity, 34-fold greater NADH nitroreductase activity, and eightfold greater nicotinamide adenine dinucleotide phosphate (NADPH) nitroreductase activity than cytosolic fractions from matched MtrR strains. Electrophoresis of cytosolic fractions in non-denaturing gels showed up to 10 protein bands when stained with Coomassie blue. Activity staining of non-denaturing, non-reducing polyacrylamide gels detected NAD(P)H oxidase, disulphide reductase, tetrazolium reductase and nitroreductase activities in the protein bands. Oxidase and reductase activities observed in a band from MtrS strains were absent in the corresponding band from MtrR strains. This band comprised at least 13 proteins, and the major constituent was identified as an alkyl hydroperoxide reductase AhpC subunit. The absence of oxidase and reductase activities in the band from MtrR strains indicated a correlation between the activity of the proteins in this band and the metronidazole-sensitive phenotype.     

Primary resistance of Helicobacter pylori to antimicrobial agents in Polish children

Helicobacter pylori resistance to antimicrobial agents is an important factor compromising the efficacy of treatment. Therefore the aims of our study were: to determine the prevalence of H. pylori resistance to clarithromycin, metronidazole, amoxycillin and tetracycline in children prior to eradication therapy, to compare different methods of susceptibility testing and to detect mutations responsible for clarithromycin resistance. During 1996-2000, 259 H. pylori strains were isolated from antral gastric biopsies. Susceptibility to antimicrobials was determined by the agar dilution method and the Etest. Mutations in the 23S rRNA gene associated with clarithromycin resistance were analysed by PCR-RFLP and direct sequencing. Overall, ninety-six strains (37%) were resistant to metronidazole, 50 strains (19.3%) were resistant to clarithromycin, and 20 strains (7.7%) were simultaneously resistant to both drugs. All cultured isolates were sensitive to amoxycillin and only one isolate (0.4%) was resistant to tetracycline. The agar dilution method and the Etest showed a perfect category correlation for clarithromycin and 4% discrepancies for metronidazole. Primary resistance to clarithromycin was mainly associated with an A2143G mutation in the 23S rRNA gene of H. pylori. The study highlights the high prevalence of H. pylori primary resistance to clarithromycin in Polish children, which implies a need for pretreatment susceptibility testing.     

Helicobacter pylori disulphide reductases: role in metronidazole reduction

Disulphide reductases play an important role in maintaining intracellular redox potential. Three disulphide reductase activities were identified in Helicobacter pylori, which used dithiobis-2-nitrobenzoic acid, glutathione or l-cystine and ferredoxin as substrates. The kinetic parameters of these activities were determined and it was demonstrated that the reductase activities were inhibited by the presence of metronidazole. Substrate competition experiments served to show inhibition of metronidazole reduction by dithiobis-2-nitrobenzoic acid, glutathione and ferredoxin in lysates from metronidazole susceptible and resistant matched pairs of strains. The study demonstrated that the activities of three disulphide reductases were modulated by the presence of metronidazole, and that metronidazole reduction was inhibited by the presence of disulphide reductase substrates.     

An Increase in Helicobacter pylori Strains Resistant to Metronidazole: A Five-Year Study

Background. Metronidazole is one of the most commonly used antimicrobial agents for the treatment of Helicobacter pylori infection. Resistance to metronidazole has been reported worldwide but with a wide range of prevalence. We started using the classical triple therapy (bismuth, tetracycline, and metronidazole) for H. pylori infection in 1991 but recently have experienced a decline in its efficacy in curing the infection. Thus our aim was to investigate in a single center the prevalence of metronidazole-resistant H. pylori over a period of 5 years.
Materials and Methods. A total of 1,015 different H. pylori strains collected over a period of 5 years were tested for sensitivity against metronidazole, ampicillin, tetracycline, and imipenem. Antibiotic sensitivity was tested by the disk diffusion and agar dilution methods. To elucidate further the possible relationship between these metronidazole-resistant strains, genomic DNA digestion by the Hae III endonuclease and ribotyping were undertaken in a selected group of isolates.
Results. In 1991, 29 of 132 (22.0%) tested strains of H. pylori were found to be resistant to metronidazole. Since our initiation at that time of a triple therapy of bismuth, metronidazole, and tetracycline, the prevalence of metronidazole-resistant strains rose rapidly to 73.2% in 1995. All H. pylori isolates were sensitive to ampicillin, tetracycline, and imipenem. A high degree of genomic heterogeneity was found among these isolates. Thus it is unlikely that the resistant strains of H. pylori were originated from a single clone.
Conclusions. This study shows a rapid increase in metronidazole-resistant H. pylori with the use of an anti- Helicobacter regimen that contains metronidazole. We anticipate that the efficacy of metronidazole-containing anti- Helicobacter regimens will decline with the rapid rise in resistant strains of H. pylori.     

The fdxA ferredoxin gene can down-regulate frxA nitroreductase gene expression and is essential in many strains of Helicobacter pylori

Very few examples of metabolic regulation are known in the gastric pathogen Helicobacter pylori. An unanticipated case was suggested, however, upon finding two types of metronidazole (Mtz)-susceptible strains: type I, in which frxA (which encodes a nitroreductase that contributes to Mtz susceptibility) is quiescent, and type II, in which frxA is well expressed. Here we report that inactivation of the fdxA ferredoxin gene (hp277) in type I strains resulted in high-level frxA expression (in effect, making them type II). However, fdxA null derivatives were obtained from only 6 of 32 type I strains tested that were readily transformed with an frxA::aphA marker. This suggested that fdxA is often essential. This essentiality was overcome in 4 of 20 strains by inactivating frxA, which suggested both that frxA overexpression is potentially deleterious and also that fdxA has additional, often vital roles. With type II strains, in contrast, fdxA null derivatives were obtained in 20 of 23 cases tested. Thus, fdxA is dispensable in most strains that normally exhibit (and tolerate) strong frxA expression. We propose that restraint of frxA expression helps maintain balanced metabolic networks in most type I strains, that other homeostatic mechanisms predominate in type II strains, and that these complex results constitute a phenotypic manifestation of H. pylori's great genetic diversity.     

Mutations in the 16S rRNA genes of Helicobacter pylori mediate resistance to tetracycline

Low-cost and rescue treatments for Helicobacter pylori infections involve combinations of several drugs including tetracycline. Resistance to tetracycline has recently emerged in H. pylori. The 16S rRNA gene sequences of two tetracycline-resistant clinical isolates (MIC = 64 microg/ml) were determined and compared to the consensus H. pylori 16S rRNA sequence. One isolate had four nucleotide substitutions, and the other had four substitutions and two deletions. Natural transformation with the 16S rRNA genes from the resistant organisms conferred tetracycline resistance on susceptible strains. 16S rRNA genes containing the individual mutations were constructed and tested for the ability to confer resistance. Only the 16S rRNA gene containing the triple mutation, AGA965-967TTC, was able to confer tetracycline resistance on H. pylori 26695. The MICs of tetracycline for the transformed strains were equivalent to those for the original clinical isolates. The two original isolates were also metronidazole resistant, but this trait was not linked to the tetracycline resistance phenotype. Serial passage of several H. pylori strains on increasing concentrations of tetracycline yielded mutants with only a very modest increase in tetracycline resistance to a MIC of 4 to 8 microg/ml. These mutants all had a deletion of G942 in the 16S rRNA genes. The mutations in the 16S rRNA are clearly responsible for tetracycline resistance in H. pylori.     

幽门螺杆菌耐甲硝唑基因分型与耐药性关系研究

目的：了解幽门螺杆菌（Hp）对甲硝唑的耐药株状况,探讨耐甲硝唑基因分型与耐药性的关系。方法：分离培养Hp,以纸片扩散法检测Hp对甲硝唑的耐药性,再用PCR方法扩增甲硝唑耐药基因,用RFLP方法进行基因分型,最后比较基因型与耐药性的关系。结果：武汉地区人群Hp对甲硝唑耐药率为67％,耐药株基因型与耐药性有相关性。结论：可以以基因型鉴定Hp对甲硝唑的耐药性,此方法,稳定可靠。     

Mechanism of metronidazole-resistance by isolates of nitroreductase-producing Enterococcus gallinarum and Enterococcus casseliflavus from the human intestinal tract

Enterococcus casseliflavus and Enterococcus gallinarum strains resistant to metronidazole, nitrofurantoin and nitrofurazone were isolated from fecal samples of a patient with recurrent ulcerative colitis treated with metronidazole. Unlike other metronidazole-resistant bacteria, these strains produced nitroreductase but metabolized metronidazole to compounds that could not be detected by liquid chromatography with UV or mass spectral analysis. Metronidazole-susceptible Clostridium perfringens grew equally well in spent cultures of Enterococcus spp. incubated with or without metronidazole. These data indicate that the nitroreductases produced by these Enterococcus strains did not activate metronidazole to bactericidal metabolites and these bacteria may reduce the effectiveness of metronidazole. We have indirect evidence for an alternative pathway that results in metronidazole resistance. These strains of enterococcus had nitroreductase so resistance should not have occurred.     

Pretreatment antimicrobial susceptibilities of paired gastric Helicobacter pylori isolates: antrum versus corpus

Background. Antimicrobial susceptibility testing of Helicobacter pylori isolates is the most useful tool for guiding specific therapy, especially when primary resistance is suspected. However, the most informative gastric biopsy site for detection of resistant H. pylori isolates is uncertain. We sought to determine whether susceptibilities to commonly used antimicrobials (amoxicillin, clarithromycin, minocycline, and metronidazole) were related to biopsy site.
Methods. H. pylori isolates were obtained from patients who had duodenal ulcer and had not received any therapy directed against H. pylori. Agar-dilution minimum inhibitory concentrations of each antimicrobial were compared between paired H. pylori isolates from the antrum and the proximal corpus.
Results. Differences in minimum inhibitory concentrations exceeding twofold were observed within the pairs of H. pylori isolates in 5 of the 40 patients tested. In three patients with clarithromycin-resistant isolates and two with metronidazole-resistant isolates, both antral and corporeal specimens revealed resistance. However, no patient had pairs of isolates categorized as resistant at one site and sensitive at the other.
Conclusions. While we found that an individual may have a mixed H. pylori infection with respect to differing antimicrobial susceptibility in different parts of the stomach, a single biopsy specimen from either the antrum or the corpus should provide reliable detection of H. pylori isolates with primary resistance.     

Synthesis and in vitro selective anti-Helicobacter pylori activity of pyrazoline derivatives

In order to develop new anti-Helicobacter pylori agents, a series of N1-substituted 3,5-diphenyl pyrazolines P1-P13 was prepared and evaluated for their antibacterial activity. All synthesized compounds showed little or no activity against different species of Gram-positive and Gram-negative bacteria of clinical relevance and against various strains of pathogenic fungi. The same derivatives exhibited a significant degree of activity against a range of H. pylori strains, including those resistant to the reference compound metronidazole. Among the prepared compounds those with an N1-acetyl group and a 4-methoxy substituent in the 5-phenyl ring showed the best activity against H. pylori metronidazole resistant strains in the 1-4 microg/mL MIC range.     

Anti-Helicobacter pylori agents endowed with H2-antagonist properties

New anti-Helicobacter pylori (H. pylori) agents endowed with H2-antagonists properties were obtained by combining the lamtidine derived pharmacophoric group with the antibiotic calvatic acid. All the compounds were tested for their irreversible H2-antagonist properties and for their ability to inhibit 20 H. pylori strains, two of them metronidazole resistant. The most active derivative (compound 4) displayed antimicrobial activity similar to metronidazole.     

Prevalence of Primary Fluoroquinolone Resistance Among Clinical Isolates of Helicobacter pylori at a University Hospital in Southern Taiwan

Background:  Fluoroquinolone-containing therapy is effective in eradicating Helicobacter pylori . However, the resistance rate of H. pylori to fluoroquinolones in Taiwan has not yet been reported. In this study, we aimed to investigate the susceptibility to antibiotics commonly used in eradication schedules and fluoroquinolones in H. pylori .
Methods:  A total of 210 clinical isolates of H. pylori were collected from April 1998 to September 2007 from patients in southern Taiwan. The in vitro activities of six antimicrobial agents were determined by the agar dilution method and Etest. The mutations in quinolone resistance-determining regions of gyrA and gyrB were investigated by direct sequencing.
Results:  Overall, 5.7% of the isolates were resistant to ciprofloxacin and levofloxacin. The resistance rate to amoxicillin, clarithromycin, metronidazole, and tetracycline was 1.0% (two of 210), 9.5% (20 of 210), 27.6% (58 of 210), and 0.5% (one of 210), respectively. The resistance rate to either ciprofloxacin or to levofloxacin increased from 2.8% (1998–2003) to 11.8% (2004–2007). The mutations in gyrA at N87 or D91 had an impact on primary fluoroquinolone resistance in H. pylori . Garenoxacin, but not moxifloxacin, had a good in vitro inhibitory effect against ciprofloxacin/levofloxacin-resistant strains compared with objective minimal inhibitory concentration values.
Conclusions:  Drug resistance to ciprofloxacin and levofloxacin in H. pylori collected from 2004 to 2007 increased significantly compared with resistance level observed during 1998–2003. The continuous surveillance of quinolone resistance among H. pylori is important in this area.     

Isogenic variation of Helicobacter pylori strain resulting in heteroresistant antibacterial phenotypes in a single host in vivo

BACKGROUND: Antibiotic-susceptible and -resistant Helicobacter pylori can be present simultaneously in the same host. The aim of this study was to evaluate the genomic diversity of H. pylori strains resulting in heteroresistant antibacterial phenotypes. MATERIALS AND METHODS: Twenty-one pairs of H. pylori strains isolated from the antrum and body displaying heteroresistant antibacterial phenotypes were included. We compared the genotypes of paired-isolates by random arbitrarily primed polymerase chain reaction (PCR), flagella gene PCR-based restriction fragment length polymorphism, and flaA gene sequencing. In metronidazole-heteroresistant isolates, the sequence variation of rdxA and frxA genes was analyzed using phylogenetic analysis. RESULTS: The DNA fingerprinting patterns of the paired isolates revealed that 12 pairs (57.1%) were identical, whereas one pair (3.8%) was different. The remaining eight pairs (38.1%) of isolates showed minor heterogenecity in fingerprinting patterns. In flaA gene sequencing, these identical and similar isolates showed close sequence similarity between the antrum and body, whereas different isolate showed 31 points of different nucleotide sequences. Phylogenetic analysis of the metronidazole-heteroresistant pairs showed consistent genetic relatedness of each paired isolates despite the sequence variation of the rdxA or frxA genes in five pairs (71.4%). CONCLUSIONS: These results suggest that continuing genomic diversities in the same strain may play an important role in modulating the antibiotic-heteroresistant H. pylori in vivo.