Insertion of mini-IS605 and deletion of adjacent sequences in the nitroreductase (rdxA) gene cause metronidazole resistance in Helicobacter pylori NCTC11637

Investigation of metronidazole resistance-associated mutations and virulence genotypes in helicobacter pylori isolates from the Egyptian population: A cross-sectional study

INTRODUCTION

This cross-sectional study assesses the prevalence of metronidazole resistance-associated mutations and virulence genotypes in Helicobacter pylori (H. pylori) strains isolated from the Egyptian population. H. pylori infection is a significant public health concern, with antibiotic resistance challenging its eradication.

METHODS

Gastric biopsy samples were collected from symptomatic patients referred for upper gastrointestinal endoscopy at selected healthcare facilities. The study included 250 participants with symptoms suggestive of H. pylori infection and aged 18 years or older. Biopsy samples were obtained using standard endoscopic techniques, and H. pylori strains were isolated and identified in the laboratory. Antimicrobial susceptibility testing was conducted using standard methods. Molecular analysis, including polymerase chain reaction (PCR) and sequencing, was performed to identify metronidazole resistance-associated mutations (rdxA and frxA) and virulence genotypes (cagA and vacA).

RESULTS

Antimicrobial susceptibility testing revealed that 43.6 % of the isolates were resistant to metronidazole, while 11.8 %, 4.5 %, and 55.4 % were resistant to clarithromycin, amoxicillin, and levofloxacin. Molecular analysis identified rdxA and frxA mutations in 36.3 % and 31.8 % of the isolates, respectively, indicating metronidazole resistance-associated mutations. Additionally, 60.0 % of the isolates were positive for the cagA gene, and 80.0 % had the vacA s1 type, both associated with increased virulence. A significant association was found between metronidazole resistance and the presence of cagA gene, vacA s1 type, rdxA mutation, and frxA mutation. Statistical analysis revealed associations between specific mutations and virulence genotypes with respective odds ratios, indicating higher likelihoods of metronidazole resistance in isolates exhibiting these genetic characteristics.

CONCLUSIONS

This study highlights the prevalence of metronidazole resistance and the association between specific mutations and virulence genotypes in H. pylori strains isolated from the Egyptian population. The findings underscore the importance of monitoring antibiotic resistance patterns and understanding the genetic determinants of virulence in H. pylori for effective management and treatment strategies.

Prevalence of metronidazole resistance and Helicobacter pylori infection in Moroccan children: a cross-sectional study

Introduction

the prevalence of Helicobacter pylori (H. pylori) infection in children is very high in Morocco. Eradication rates of H. pylori infection decrease due to the emergence of resistance to antibiotics. Data on the antimicrobial susceptibility of H. pylori in Moroccan children are not available. This study aims to assess the prevalence of H. pylori infection and the metronidazole resistance rate of H. pylori in Moroccan pediatric patients, and their association with epidemiologic factors.

Methods

a cross-sectional study was conducted on 132 pediatric patients who had an indication for upper gastrointestinal endoscopy and attended pediatric hospital Abderrahim Harouchi of the University Hospital Ibn Rochd, Casablanca, Morocco. Detection of H. pylori infection and the susceptibility to metronidazole was performed by classic PCR. Statistical analysis was performed using R Studio software.

Results

the overall prevalence of H. pylori infection was 80.3%. vomiting was significantly associated with H. pylori infection (p-value=0.01). Regarding the resistance rate of metronidazole, we found that the prevalence of H. pylori resistance to metronidazole was high (70.8%) and it significantly increased, especially in pediatric patients living in urban areas (p-value=0.01).

Conclusion

the prevalence of H. pylori infection and resistance rate of metronidazole were very high in Moroccan children. Therefore, triple therapy with metronidazole must be preceded by a study of the bacterium's susceptibility to the prescribed antibiotics, in particular to metronidazole.

Metagenomic profiling of antibiotic resistance genes in Red Sea brine pools

Antibiotic resistance (AR) is an alarming global health concern, causing an annual death rate of more than 35,000 deaths in the US. AR is a natural phenomenon, reported in several pristine environments. In this study, we report AR in pristine Red Sea deep brine pools. Antimicrobial resistance genes (ARGs) were detected for several drug classes with tetracycline and macrolide resistance being the most abundant. As expected, ARGs abundance increased in accordance with the level of human impact with pristine Red Sea samples having the lowest mean ARG level followed by estuary samples, while activated sludge samples showed a significantly higher ARG level. ARG hierarchical clustering grouped drug classes for which resistance was detected in Atlantis II Deep brine pool independent of the rest of the samples. ARG abundance was significantly lower in the Discovery Deep brine pool. A correlation between integrons and ARGs abundance in brine pristine samples could be detected, while insertion sequences and plasmids showed a correlation with ARGs abundance in human-impacted samples not seen in brine pristine samples. This suggests different roles of distinct mobile genetic elements (MGEs) in ARG distribution in pristine versus human-impacted sites. Additionally, we showed the presence of mobile antibiotic resistance genes in the Atlantis II brine pool as evidenced by the co-existence of integrases and plasmid replication proteins on the same contigs harboring predicted multidrug-resistant efflux pumps. This study addresses the role of non-pathogenic environmental bacteria as a silent reservoir for ARGs, and the possible horizontal gene transfer mechanism mediating ARG acquisition.

Automated extraction of genes associated with antibiotic resistance from the biomedical literature

The detection of bacterial antibiotic resistance phenotypes is important when carrying out clinical decisions for patient treatment. Conventional phenotypic testing involves culturing bacteria which requires a significant amount of time and work. Whole-genome sequencing is emerging as a fast alternative to resistance prediction, by considering the presence/absence of certain genes. A lot of research has focused on determining which bacterial genes cause antibiotic resistance and efforts are being made to consolidate these facts in knowledge bases (KBs). KBs are usually manually curated by domain experts to be of the highest quality. However, this limits the pace at which new facts are added. Automated relation extraction of gene-antibiotic resistance relations from the biomedical literature is one solution that can simplify the curation process. This paper reports on the development of a text mining pipeline that takes in English biomedical abstracts and outputs genes that are predicted to cause resistance to antibiotics. To test the generalisability of this pipeline it was then applied to predict genes associated with Helicobacter pylori antibiotic resistance, that are not present in common antibiotic resistance KBs or publications studying H. pylori. These genes would be candidates for further lab-based antibiotic research and inclusion in these KBs. For relation extraction, state-of-the-art deep learning models were used. These models were trained on a newly developed silver corpus which was generated by distant supervision of abstracts using the facts obtained from KBs. The top performing model was superior to a co-occurrence model, achieving a recall of 95%, a precision of 60% and F1-score of 74% on a manually annotated holdout dataset. To our knowledge, this project was the first attempt at developing a complete text mining pipeline that incorporates deep learning models to extract gene-antibiotic resistance relations from the literature. Additional related data can be found at https://github.com/AndreBrincat/Gene-Antibiotic-Resistance-Relation-Extraction

Mutations associated with Helicobacter pylori antimicrobial resistance in the Ecuadorian population

AIMS

We described the presence of Helicobacter pylori (HP) and estimated the prevalence of primary and secondary resistance using molecular detection in gastric biopsies of Ecuadorian patients.

METHODS AND RESULTS

66.7% (238/357) of the patients demonstrated the presence of HP using CerTest qPCR. Of these, 69.79% (104/149) were without previous HP eradication treatment and 64.42% (134/208) with prior HP eradication treatment. The mutation-associated resistance rate for clarithromycin was 33.64% (primary resistance) and 32.82% (secondary resistance), whereas that in levofloxacin the primary and secondary resistance was 37.38% and 42%, respectively. For tetracycline and rifabutin, primary and secondary resistance was 0%. Primary and secondary resistance for metronidazole and amoxicillin could not be evaluated by genotypic methods (PCR and sequencing).

CONCLUSIONS

The analysis of mutations in gyrA, 23S rRNA and 16S rRNA is useful to detect bacterial resistance as a guide for eradication therapy following failure of the first-line regimen.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study carried out in an Ecuadorian population indicates that the resistance of HP to first-line antibiotics is high, which may contribute to the high rates of treatment failure, and other treatment alternatives should be considered.

Antimicrobial resistance and virulence in Helicobacter pylori: Genomic insights

Microbes evolve rapidly by modifying their genome through mutations or acquisition of genetic elements. Antimicrobial resistance in Helicobacter pylori is increasingly prevalent in India. However, limited information is available about the genome of resistant H. pylori isolated from India. Our pan- and core-genome based analyses of 54 Indian H. pylori strains revealed plasticity of its genome. H. pylori is highly heterogenous both in terms of the genomic content and DNA sequence homology of ARGs and virulence factors. We observed that the H. pylori strains are clustered according to their geographical locations. The presence of point mutations in the ARGs and absence of acquired genetic elements linked with ARGs suggest target modifications are the primary mechanism of its antibiotic resistance. The findings of the present study would help in better understanding the emergence of drug-resistant H. pylori and controlling gastric disorders by advancing clinical guidance on selected treatment regimens.

2D Strategy for the Construction of an Enzyme-Activated NIR Fluorophore Suitable for the Visual Sensing and Profiling of Homologous Nitroreductases from Various Bacterial Species

Nitroreductases (NTRs) mediate the reduction of nitroaromatic compounds to the corresponding nitrite, hydroxylamine, or amino derivatives. The activity of NTRs in bacteria facilitates the metabolic activation and antibacterial activity of 5-nitroimidazoles. Therefore, NTR activity correlates with the drug susceptibility and resistance of pathogenic bacteria. As such, it is important to develop a rapid and visual assay for the real-time sensing of bacterial NTRs for the evaluation and development of antibiotics. Herein, an activatable near-infrared fluorescent probe (HC-NO2) derived from a hemicyanine fluorophore was designed and developed based on two evaluation factors, including the calculated partition coefficient (Clog P) and fluorescence wavelength. Using HC-NO2 as the special substrate of NTRs, NTR activity can be assayed efficiently, and then, bacteria can be imaged based on the detection of NTRs. More importantly, a sensitive in-gel assay using HC-NO2 has been developed to selectively identify NTRs and sensitively determine NTR activity. Using the in-gel assay, NTRs from various bacterial species have been profiled visually from the "fluorescence fingerprints", which facilitates the rapid identification of NTRs from bacterial lysates. Thus, various homologous NTRs were identified from three metronidazole-susceptible bacterial species as well as seven unsusceptible species, which were confirmed by the whole-genome sequence. As such, the evaluation of NTRs from different bacterial species should help improve the rational usage of 5-nitroimidazole drugs as antibiotics.

Effect of Temperature on Metronidazole Resistance in Helicobacter pylori

Efficacy of Helicobacter pylori (H. pylori) eradication therapy has declined due to rapid rises in antibiotic resistance. We investigated how increased temperature affected H. pylori (NCTC 11637) growth and its sensitivity to metronidazole in vitro. We performed transcriptomic profiling using RNA-sequencing to identify differentially expressed genes (DEGs) associated with increased temperature. Transcriptional pathways involved in temperature-driven metronidazole resistance changes were analyzed through bioinformatic and literature curation approaches. We showed that H. pylori growth was inhibited at 41°C and inhibition was more apparent with prolonged incubation. Resistance to metronidazole was also reduced—minimum inhibitory concentration for metronidazole decreased from > 256 μg/ml at 37°C to 8 μg/ml at 41°C after culturing for 3 days. RNA-sequencing results, which were highly concordant within treatment conditions, revealed more than one third of genes (583/1,552) to be differentially expressed at increased temperatures with similar proportions up and down-regulated. Quantitative real-time PCR validation for 8 out of 10 DEGs tested gave consistent direction in gene expression changes. We found enrichment for redox and oxygen radical pathways, highlighting a mechanistic pathway driving temperature-related metronidazole resistance. Independent literature review of published genes associated with metronidazole resistance revealed 46 gene candidates, 21 of which showed differential expression and 7 out of 9 DEGs associated with “redox” resistance pathways. Sanger sequencing did not detect any changes in genetic sequences for known resistance genes rdxA, frxA nor fdxB. Our findings suggest that temperature increase can inhibit the growth and reduce H. pylori resistance to metronidazole. Redox pathways are possible potential drivers in metronidazole resistance change induced by temperature. Our study provides insight into potential novel approaches in treating antibiotic resistant H. pylori.

Efficacy of quadruple regimen with polaprezinc for gastric Helicobacter pylori infection eradication: protocol for a single-centre, single-blind, non-inferiority, randomised clinical trial

INTRODUCTION

Helicobacter pylori (H. pylori) is the most well-known risk factor for gastric cancer. At present, H. pylori shows varying levels of resistance to different treatments, leading to a lower rate of H. pylori eradication. The aim of this study is to evaluate the efficacy of polaprezinc-containing quadruple therapy (PQT) for the eradication of H. pylori infection and, thus, to provide more evidence to inform the clinical treatment of H. pylori infection in China.

METHODS AND ANALYSIS

This is a single-centre, single-blind, non-inferiority, randomised controlled trial, enrolling 158 patients with H. pylori infection. Patients are randomised (1:1) to the two groups for a 14-day therapy. Treatment group: PQT (esomeprazole 20 mg, amoxicillin 1 g, clarithromycin 500 mg, polaprezinc 75 mg) two times per day; control group: bismuth-containing quadruple therapy (esomeprazole 20 mg, amoxicillin 1 g, clarithromycin 500 mg, bismuth potassium citrate 220 mg) two times per day. The primary outcome is the rate of H. pylori eradication. Secondary outcomes are the incidence of adverse events and the gastrointestinal microbiota distribution. The 16S ribosomal RNA (16S rRNA) next-generation sequencing (NGS) is used to evaluate the effect of two different therapies on the distribution of the gastrointestinal microbiota.

ETHICS AND DISSEMINATION

This study was approved by the Ethics Committee of Sichuan Cancer Center & Hospital (No. SCCHEC-02-2019-015). Any amendment to the research protocol will be submitted for ethical approval. All participants must provide informed consent. On completion, the results of the study will be published in the appropriate peer-reviewed journal.

TRIAL REGISTRATION NUMBER

ChiCTR1900025800; preresults.

Antibiotic resistance in Helicobacter pylori: A mutational analysis from a tertiary care hospital in Kashmir, India

Background

Helicobacter pylori infection is recognised as type 1 carcinogen by the International Agency of Research on Cancer. Previous studies in our hospital have revealed high prevalence of H. pylori in our population with a high recurrence rate after completion of treatment. This prompted us to undertake this study.

Aim

This study aimed to determine common gene mutations leading to resistance to clarithromycin, metronidazole, tetracycline and quinolones in H. pylori in patients attending our hospital.

Settings and Design

This is a cross-sectional hospital-based study. The study was approved by the Institutional Ethics Committee.

Materials and Methods

This study was conducted on 196 adult dyspeptic patients with an indication for upper gastrointestinal endoscopy. Gastric biopsies collected from them were subjected to histopathological examination, rapid urease test (RUT) and culture. Of the 196 patients, 95 met the inclusion criteria. Drug susceptibility testing (DST) by various polymerase chain reaction-based methods was done for 47 RUT-positive biopsies and 13 H. pylori isolates.

Results

Maximum resistance was seen to metronidazole (81.66%) followed by clarithromycin (45%) and quinolones (3.33%). No high-level resistance was seen to tetracycline. In clarithromycin-resistant cases, A2142G mutation was more prevalent than A2143G mutation. Multidrug resistance (resistance to metronidazole and clarithromycin) was seen in 41.66% of patients.

Conclusions

Tetracycline and quinolones could be the antibiotics of choice in the eradication of H. pylori in this region, while recurrence of the infection with H. pylori could be expected among patients receiving either metronidazole or clarithromycin, for eradication therapy. DST should be done on a routine basis utilising both phenotypic and genotypic methods to prevent further emergence of resistance in this region.

A review on metronidazole: an old warhorse in antimicrobial chemotherapy

The 5-nitroimidazole drug metronidazole has remained the drug of choice in the treatment of anaerobic infections, parasitic as well as bacterial, ever since its development in 1959. In contrast to most other antimicrobials, it has a pleiotropic mode of action and reacts with a large number of molecules. Importantly, metronidazole, which is strictly speaking a prodrug, needs to be reduced at its nitro group in order to become toxic. Reduction of metronidazole, however, only takes place under very low concentrations of oxygen, explaining why metronidazole is exclusively toxic to microaerophilic and anaerobic microorganisms. In general, resistance rates amongst the pathogens treated with metronidazole have remained low until the present day. Nevertheless, metronidazole resistance does occur, and for the treatment of some pathogens, especially Helicobacter pylori, metronidazole has become almost useless in some parts of the world. This review will give an account on the current status of research on metronidazole's mode of action, metronidazole resistance in eukaryotes and prokaryotes, and on other 5-nitroimidazoles in use.

Helicobacter pylori-Clarithromycin Resistance in Symptomatic Pediatric Patients in a High Prevalence Country

INTRODUCTION

Failure to eradicate Helicobacter pylori despite antibiotic treatment is generally attributed to increasing clarithromycin resistance conferred by point mutations in the 23S-rRNA gene or metronidazole resistance attributed to rdxA gene (HP0954) deletion in patients. Scarce data for pediatric population are available from developing countries.

OBJECTIVES

The aim of the present study was to determine the presence of A2142G/C and A2143G mutations in the 23S-rRNA gene and/or rdxA gene (HP0954) deletion in a group of symptomatic H pylori-infected children recruited from an area with high infection rate and risk of gastric cancer.

PATIENTS AND METHODS

We recruited 118 patients referred for upper endoscopy for gastrointestinal symptoms. The presence of H pylori was determined by urease test and histological staining. The rdxA gene (HP0954) deletion, and 2142G/C and A2143G mutations were determined by polymerase chain reaction-restriction fragment length polymorphism. A subgroup of infected patients received a 14-day regimen of omeprazole, amoxicillin, and clarithromycin. The effectiveness of this regime was determined by stool antigen determination 8 weeks after treatment.

RESULTS

About 21% of the analyzed infected patients showed mutation in the 23S-rRNA gene, with the A2143G transition as the more frequent mutation, and 2% of the patients showed rdxA gene (HP0954) deletion. After treatment, 25% of the patients continued to harbor the bacteria; of these, 67% carried the A2143G mutation.

CONCLUSIONS

H pylori-infected pediatric patients from Chile show high prevalence of the mutation responsible for clarithromycin resistance. The failure to eradicate H pylori can be attributed to the presence of the A2143G mutation.

GENETIC MUTATIONS AFFECTING THE FIRST LINE ERADICATION THERAPY OF Helicobacter pylori-INFECTED EGYPTIAN PATIENTS

Introduction:

Several genetic mutations affect the first-line triple therapy for Helicobacter pylori. We aimed to study the most common genetic mutations affecting the metronidazole and clarithromycin therapy for H. pylori-infected Egyptian patients.

Patients and Methods:

In our study, we included 100 successive dyspeptic patients scheduled for diagnosis through upper gastroscopy at Cairo's University Hospital, Egypt. Gastric biopsies were tested for the presence of H. pylori by detection of the 16S rRNA gene. Positive biopsies were further studied for the presence of the rdxA gene deletion by Polymerase Chain Reaction (PCR), while clarithromycin resistance was investigated by the presence of nucleotide substitutions within H. pylori 23S rRNA V domain using MboII and BsaI to carry out a Restricted Fragment Length Polymorphism (RFLP) assay.

Results:

Among 70 H. pylori positive biopsies, the rdxA gene deletion was detected in 44/70 (62.9%) samples, while predominance of the A2142G mutations within the H. pylori 23S rRNA V domain was evidenced in 39/70 (55.7%) of the positive H. pylori cases. No statistically significant difference was found between the presence of gene mutations and different factors such as patients 'age, gender, geographic distribution, symptoms and endoscopic findings.

Conclusion:

Infection with mutated H. pylori strains is considerably high, a finding that imposes care in the use of the triple therapy to treat H. pylori in Egypt, since the guidelines recommend to abandon the standard triple therapy when the primary clarithromycin resistance rate is over 20%¹.

Search for novel candidate mutations for metronidazole resistance in Helicobacter pylori using next-generation sequencing

Metronidazole resistance is a key factor associated with Helicobacter pylori treatment failure. Although this resistance is mainly associated with mutations in the rdxA and frxA genes, the question of whether metronidazole resistance is caused by the inactivation of frxA alone is still debated. Furthermore, it is unclear whether there are other mutations involved in addition to the two genes that are associated with resistance. A metronidazole-resistant strain was cultured from the metronidazole-susceptible H. pylori strain 26695-1 by exposure to low concentrations of metronidazole. The genome sequences of both susceptible and resistant H. pylori strains were determined by Illumina next-generation sequencing, from which putative candidate resistance mutations were identified. Natural transformation was used to introduce PCR products containing candidate mutations into the susceptible parent strain 26695-1, and the metronidazole MIC was determined for each strain. Mutations in frxA (hp0642), rdxA (hp0954), and rpsU (hp0562) were confirmed by the Sanger method. The mutated sequence in rdxA was successfully transformed into strain 26695-1, and the transformants showed resistance to metronidazole. The transformants containing a single mutation in rdxA showed a low MIC (16 mg/liter), while those containing mutations in both rdxA and frxA showed a higher MIC (48 mg/liter). No transformants containing a single mutation in frxA or rpsU were obtained. Next-generation sequencing was used to identify mutations related to drug resistance. We confirmed that the mutations in rdxA are mainly associated with metronidazole resistance, and mutations in frxA are able to enhance H. pylori resistance only in the presence of rdxA mutations. Moreover, mutations in rpsU may play a role in metronidazole resistance.

Lon protease affects the RdxA nitroreductase activity and metronidazole susceptibility in Helicobacter pylori

BACKGROUND

The lon gene of Helicobacter pylori strains is constitutively expressed during growth. However, virtually nothing is understood concerning the role of Lon in H. pylori. This study examined the function and physiological role of Lon in H. pylori (HpLon) using a trapping approach to identify putative Lon binding partners in the bacterium.

MATERIALS AND METHODS

Protease-deficient Lon was expressed and served as the bait in trapping approach to capture the interacting partners in H. pylori. The antibiotic susceptibility of wild-type and lon derivative mutants was determined by the E test trips and the disc diffusion assay. The effect of HpLon on RdxA activity was detected the change in NADPH oxidation and metronidazole reduction by spectrophotometer.

RESULTS

Lon in Helicobacter pylori (HpLon) interacting partners are mostly associated with metronidazole activation. lon mutant presents more susceptible to metronidazole than that of the wild type, and this phenotype is recovered by complementation of the wild-type Lon. We found that the ATPases associated with a variety of cellular activities (AAA(+) ) module of HpLon causes a decrease in both NADPH oxidase and Mtz reductase activity in RdxA, a major Mtz-activating enzyme in H. pylori.

CONCLUSION

Metronidazole resistance of H. pylori causes the serious medical problem worldwide. In this study, HpLon is involved in metronidazole susceptibility among H. pylori strains. We provide the evidence that HpLon alters RdxA activity in vitro. The decrease in metronidazole activation caused by HpLon is possibly prior to accumulate mutation in rdxA gene before the metronidazole-resistant strains to be occurred.

The mutation of the rdxA gene in metronidazole-resistant Helicobacter pylori clinical isolates

Backgrounds:

Antibiotic resistance is an increasing problem throughout the developed world, and knowledge about different resistance mechanisms is consequential for efficient treatment of bacterial infections. Although metronidazole has been frequently used in treatment regimens for H. pylori infection, but antibiotic resistance is now a major contributing factor in treatment failure. Nevertheless metronidazole has been greatly used as a critical component of combination therapies for H. pylori infection.

Objective:

This study is trying to describe the mutational mechanisms of metronidazole resistance in H. pylori in our clinical isolates in Isfahanian patients, Iran and compare with the findings of previous studies in world.

Materials and Methods:

MIC values of metronidazole for H. pylori strains were determined by E- test. Both rdxA and glmM genes used for confirmation of isolates as H. pylori and then amplification of another rdxA oligonucleotide pair was done. Finally, the six resistant strains were sent to sequencing for other processing and further analysis was done by software.

Results:

The result of six clinical isolates in comparison with 26695, J99 and 69A as a sensitive and resistant reference strains showed plenty of mutations. No frame shift and nonsense mutation was seen in our clinical isolates.

Conclusion:

An interesting finding in metronidazole-resistant strains in our study was the detection of one mutation not previously described in the literature in the rdxA gene and this W(209)R substitution presumably plays a role in inducing metronidazole resistance.

The rOmp22-HpaA fusion protein confers protective immunity against helicobacter pylori in mice

Helicobacter pylori (H. pylori) plays an essential role in the development of various gastroduodenal diseases; however, no vaccines preventing H. pylori infection have been available now. This study was to evaluate the protective effect of rOmp22-HpaA fusion protein against H. pylori infection in mouse model and to screen the candidate to be used in the development of an oral vaccine against H. pylori. rOmp22, rHpaA, rOmp22+rHpaA, and rOmp22-HpaA groups were used to immunize mice with mLT63 as adjuvant by intragastric route, respectively, four times at 1-week intervals. Two weeks after last immunization, all of the animals were orally challenged with H. pylori NCTC11637 and then were killed after another 2 weeks. The mice gastric tissue of all groups was separated to detect the presence of infection by urease tests, to culture H. pylori, and to observe the histological characteristics. The protective effect against H. pylori challenge in mice immunized with rOmp22-HpaA fusion protein and mLT63 adjuvant was significantly higher than PBS and mLT63 control groups (P < 0.05), but no significant difference was detected among rOmp22, rHpaA, rOmp22+rHpaA, and rOmp22-HpaA groups (P > 0.05). rOmp22-HpaA fusion protein retained immunogenicity and could be used as an antigen candidate in the development of an oral vaccine against H. pylori infection.

FecA1, a bacterial iron transporter, determines the survival of Helicobacter pylori in the stomach

Helicobacter pylori encodes a single iron-cofactored superoxide dismutase (SodB), which is regulated by the ferric uptake regulator (Fur). Ferrous ion (Fe(2+)) is necessary for the activation of SodB. The activity of SodB is an important determinant of the capability of H. pylori for long-term colonization of the stomach and of the development of metronidazole (Mtz) resistance of the bacterium. This study is conducted to characterize the Fe(2+)-supply mechanisms for the activation of SodB in H. pylori, which, as mentioned above, is associated with the host-colonization ability and Mtz resistance of H. pylori. In this study, we demonstrate that fecA1, a Fe(3+)-dicitrate transporter homolog, is an essential gene for SodB activation, but not for the biogenic activity of H. pylori. H. pylori with SodB inactivation by fecA1 deletion showed reduced resistance to H(2)O(2), reduced gastric mucosal-colonization ability in Mongolian gerbils, and also reduced resistance to Mtz. Our experiment demonstrated that FecA1 is an important determinant of the host-colonization ability and Mtz resistance of H. pylori through Fe(2+) supply to SodB, suggesting that FecA1 may be a possible target for the development of a novel bactericidal drug.

Comparative genomics of Helicobacter pylori and the human-derived Helicobacter bizzozeronii CIII-1 strain reveal the molecular basis of the zoonotic nature of non-pylori gastric Helicobacter infections in humans

BACKGROUND

The canine Gram-negative Helicobacter bizzozeronii is one of seven species in Helicobacter heilmannii sensu lato that are detected in 0.17-2.3% of the gastric biopsies of human patients with gastric symptoms. At the present, H. bizzozeronii is the only non-pylori gastric Helicobacter sp. cultivated from human patients and is therefore a good alternative model of human gastric Helicobacter disease. We recently sequenced the genome of the H. bizzozeronii human strain CIII-1, isolated in 2008 from a 47-year old Finnish woman suffering from severe dyspeptic symptoms. In this study, we performed a detailed comparative genome analysis with H. pylori, providing new insights into non-pylori Helicobacter infections and the mechanisms of transmission between the primary animal host and humans.

RESULTS

H. bizzozeronii possesses all the genes necessary for its specialised life in the stomach. However, H. bizzozeronii differs from H. pylori by having a wider metabolic flexibility in terms of its energy sources and electron transport chain. Moreover, H. bizzozeronii harbours a higher number of methyl-accepting chemotaxis proteins, allowing it to respond to a wider spectrum of environmental signals. In this study, H. bizzozeronii has been shown to have high level of genome plasticity. We were able to identify a total of 43 contingency genes, 5 insertion sequences (ISs), 22 mini-IS elements, 1 genomic island and a putative prophage. Although H. bizzozeronii lacks homologues of some of the major H. pylori virulence genes, other candidate virulence factors are present. In particular, we identified a polysaccharide lyase (HBZC1_15820) as a potential new virulence factor of H. bizzozeronii.

CONCLUSIONS

The comparative genome analysis performed in this study increased the knowledge of the biology of gastric Helicobacter species. In particular, we propose the hypothesis that the high metabolic versatility and the ability to react to a range of environmental signals, factors which differentiate H. bizzozeronii as well as H. felis and H. suis from H. pylori, are the molecular basis of the of the zoonotic nature of H. heilmannii sensu lato infection in humans.

Mechanisms of Helicobacter pylori antibiotic resistance: An updated appraisal

Helicobacter pylori (H. pylori) antibiotic resistance is the main factor affecting the efficacy of the current eradicating therapies. The aim of this editorial is to report on the recent information about the mechanisms accounting for the resistance to the different antibiotics currently utilized in H. pylori eradicating treatments. Different mechanisms of resistance to clarithromycin, metronidazole, quinolones, amoxicillin and tetracycline are accurately detailed (point mutations, redox intracellular potential, pump efflux systems, membrane permeability) on the basis of the most recent data available from the literature. The next hope for the future is that by improving the knowledge of resistance mechanisms, the elaboration of rational and efficacious associations for the treatment of the infection will be possible. Another auspicious progress might be the possibility of a cheap, feasible and reliable laboratory test to predict the outcome of a therapeutic scheme.

An African perspective on Helicobacter pylori: prevalence of human infection, drug resistance, and alternative approaches to treatment

Helicobacter pylori is a Gram-negative, micro-aerophilic, motile, curved rod that inhabits the gastric mucosa of the human stomach. It chronically infects thousands of millions of people world-wide, and is one of the most genetically diverse of bacterial species. Infection with the bacterium leads to chronic gastritis, peptic ulceration, gastric cancers and gastric mucosa-associated lymphoid-tissue (MALT) lymphoma. The prevalence of infection appears to be partly determined by geographical and socio-demographic factors, being higher in Africa than elsewhere. Current treatment, based on potent combinations that each consist of a proton-pump inhibitor and two antibiotics, is successful in 80%-90% of patients. Some undesirable side-effects, poor patient compliance and drug resistance are, however, associated with significant levels of treatment failure and with contra-indications for some patients. Antibiotic resistance in H. pylori is a growing global concern that merits the urgent attention of public-health authorities. Numerous pieces of clinical evidence have revealed that eradication of the organism from a patient results in improvement of gastritis and drastically decreases the frequency of relapse of gastric and duodenal ulcers. Natural products, including medicinal plants and honey, may offer useful alternatives in the treatment of H. pylori-related infections.

Role of NADPH-insensitive nitroreductase gene to metronidazole resistance of Helicobacter pylori strains

BACKGROUND AND THE PURPOSE OF THE STUDY

Current anti-H. pylori therapies are based on the use of two antibiotics with a proton pump inhibitor and/or a bismuth component. Metronidazole is a key component of such combination therapies in Iran. The aim of this study was to determine the role of rdxA gene in resistant strains of H. pylori isolated from Shahrekord Hajar hospital to metronidazole.

METHODS

This study was a cross-sectional method, which was carried out on 263 patients who referred to endoscopy department of Hajar hospital, in 2007. Biopsy samples were cultured on selective Brucella agar containing 10% blood and incubated under microerophilic condition at 370C for 3-7 days. Suspected colonies were tested by Gram staining, urease, oxidase and catalase activities. Organisms were confirmed to be H. pylori on the basis of the presence of ureC(glmM) gene by PCR.Specific primers were used for detection of rdxA gene mutation.

RESULTS

Eighty and four strains of H. pylori determined by PCR method. Of the isolated strains, 49 (58.33%) were resistant, 7 (8.33%) were semi-sensitive to metronidazole and 200bp deletion in rdxA gene was observed in 2 strains.

CONCLUSION

Because of the high metronidazole resistance in patients under study it was necessary to replace it by other antibiotics in therapeutic regimens. On the basis of low frequency of resistance mutation in rdxA gene, sequence analysis for identification of other mechanisms is suggested.

Insertion sequence content reflects genome plasticity in strains of the root nodule actinobacterium Frankia

Background

Genome analysis of three Frankia sp. strains has revealed a high number of transposable elements in two of the strains. Twelve out of the 20 major families of bacterial Insertion Sequence (IS) elements are represented in the 148 annotated transposases of Frankia strain HFPCcI3 (CcI3) comprising 3% of its total coding sequences (CDS). EAN1pec (EAN) has 183 transposase ORFs from 13 IS families comprising 2.2% of its CDS. Strain ACN14a (ACN) differs significantly from the other strains with only 33 transposase ORFs (0.5% of the total CDS) from 9 IS families.

Results

Insertion sequences in the Frankia genomes were analyzed using BLAST searches, PHYML phylogenies and the IRF (Inverted Repeat Finder) algorithms. To identify putative or decaying IS elements, a PSI-TBLASTN search was performed on all three genomes, identifying 36%, 39% and 12% additional putative transposase ORFs than originally annotated in strains CcI3, EAN and ACN, respectively. The distribution of transposase ORFs in each strain was then analysed using a sliding window, revealing significant clustering of elements in regions of the EAN and CcI3 genomes. Lastly the three genomes were aligned with the MAUVE multiple genome alignment tool, revealing several Large Chromosome Rearrangement (LCR) events; many of which correlate to transposase clusters.

Conclusion

Analysis of transposase ORFs in Frankia sp. revealed low inter-strain diversity of transposases, suggesting that the majority of transposase proliferation occurred without recent horizontal transfer of novel mobile elements from outside the genus. Exceptions to this include representatives from the IS3 family in strain EAN and seven IS4 transposases in all three strains that have a lower G+C content, suggesting recent horizontal transfer. The clustering of transposase ORFs near LCRs revealed a tendency for IS elements to be associated with regions of chromosome instability in the three strains. The results of this study suggest that IS elements may help drive chromosome differences in different Frankia sp. strains as they have adapted to a variety of hosts and environments.

Trichomonas vaginalis: metronidazole and other nitroimidazole drugs are reduced by the flavin enzyme thioredoxin reductase and disrupt the cellular redox system. Implications for nitroimidazole toxicity and resistance

Infections with the microaerophilic parasite Trichomonas vaginalis are treated with the 5-nitroimidazole drug metronidazole, which is also in use against Entamoeba histolytica, Giardia intestinalis and microaerophilic/anaerobic bacteria. Here we report that in T. vaginalis the flavin enzyme thioredoxin reductase displays nitroreductase activity with nitroimidazoles, including metronidazole, and with the nitrofuran drug furazolidone. Reactive metabolites of metronidazole and other nitroimidazoles form covalent adducts with several proteins that are known or assumed to be associated with thioredoxin-mediated redox regulation, including thioredoxin reductase itself, ribonucleotide reductase, thioredoxin peroxidase and cytosolic malate dehydrogenase. Disulphide reducing activity of thioredoxin reductase was greatly diminished in extracts of metronidazole-treated cells and intracellular non-protein thiol levels were sharply decreased. We generated a highly metronidazole-resistant cell line that displayed only minimal thioredoxin reductase activity, not due to diminished expression of the enzyme but due to the lack of its FAD cofactor. Reduction of free flavins, readily observed in metronidazole-susceptible cells, was also absent in the resistant cells. On the other hand, iron-depleted T. vaginalis cells, expressing only minimal amounts of PFOR and hydrogenosomal malate dehydrogenase, remained fully susceptible to metronidazole. Thus, taken together, our data suggest a flavin-based mechanism of metronidazole activation and thereby challenge the current model of hydrogenosomal activation of nitroimidazole drugs.

Antimicrobial resistance induced by genetic changes

Decoding the mechanisms of resistance to antibiotics is essential in fighting a phenomenon, which is amplifying everyday due to the uncontrolled excessive and many times unjustified use of anti-microbial substances. At present it has become a matter of public health, together with the resistance of Mycobacterium tuberculosis to tuberculostatic or the spreading of the AIDS virus which not only affects the European countries but the entire globe. This paper presents the genic mutations taking place at the level of bacterial chromosome and inducing the resistance to antibiotics.

A redox basis for metronidazole resistance in Helicobacter pylori

Metronidazole resistance in Helicobacter pylori has been attributed to mutations in rdxA or frxA. Insufficient data correlating RdxA and/or FrxA with the resistant phenotype, and the emergence of resistant strains with no mutations in either rdxA or frxA, indicated that the molecular basis of H. pylori resistance to metronidazole required further characterization. The rdxA and frxA genes of four matched pairs of metronidazole-susceptible and -resistant strains were sequenced. The resistant strains had mutations in either rdxA, frxA, neither gene, or both genes. The reduction rates of five substrates suggested that metabolic differences between susceptible and resistant strains cannot be explained only by mutations in rdxA and/or frxA. A more global approach to understanding the resistance phenotype was taken by employing two-dimensional gel electrophoresis combined with tandem mass spectrometry analyses to identify proteins differentially expressed by the matched pair of strains with no mutations in rdxA or frxA. Proteins involved in the oxireduction of ferredoxin were downregulated in the resistant strain. Other redox enzymes, such as thioredoxin reductase, alkyl hydroperoxide reductase, and superoxide dismutase, showed a pI change in the resistant strain. The data suggested that metronidazole resistance involved more complex metabolic changes than specific gene mutations, and they provided evidence of a role for the intracellular redox potential in the development of resistance.

Who's Winning the War? Molecular Mechanisms of Antibiotic Resistance in Helicobacter pylori

The ability of clinicians to wage an effective war against many bacterial infections is increasingly being hampered by skyrocketing rates of antibiotic resistance. Indeed, antibiotic resistance is a significant problem for treatment of diseases caused by virtually all known infectious bacteria. The gastric pathogen Helicobacter pylori is no exception to this rule. With more than 50% of the world's population infected, H. pylori exacts a tremendous medical burden and represents an interesting paradigm for cancer development; it is the only bacterium that is currently recognized as a carcinogen. It is now firmly established that H. pylori infection is associated with diseases such as gastritis, peptic and duodenal ulceration and two forms of gastric cancer, gastric adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma. With such a large percentage of the population infected, increasing rates of antibiotic resistance are particularly vexing for a treatment regime that is already fairly complicated; treatment consists of two antibiotics and a proton pump inhibitor. To date, resistance has been found to all primary and secondary lines of antibiotic treatment as well as to drugs used for rescue therapy.

Helicobacter pylori isolates recovered from gastric biopsies of patients with gastro-duodenal pathologies in Cameroon: current status of antibiogram

OBJECTIVE

To determine the prevalence of Helicobacter pylori in patients with gastro-duodenal pathologies and the susceptibility patterns of isolates to the currently recommended antibiotic treatment regimen used in Cameroon.

METHODS

Consecutive dyspeptic patients referred to Douala General Hospital, Cameroon for endoscopy were recruited in the study. Gastric biopsies were collected from the patients and H. pylori isolated and identified following standard microbiology and biochemical techniques. Antibiotic susceptibility was determined by disk diffusion and agar dilution methods against clarithromycin, tetracycline, amoxicillin and metronidazole. Data were analysed using chi-square test and significance considered at P < 0.05.

RESULTS

Seventy-one (92.2%) of the 77 patients (mean age 44.5 +/- 15.7, range 15-77 years) were positive for H. pylori. The antibiotic susceptibility rates were 56% for tetracycline, 55.3% for clarithromycin, 14.4% for amoxicillin and 6.8% for metronidazole. The prevalence of clarithromycin resistance in males vs. females was 42.1%vs. 46.7%, while for metronidazole it was 89.5%vs. 94.7% (P > 0.05). Antimicrobial susceptibility results also revealed 12 antibiotypes based on resistance to the antimicrobial agents investigated. The resistance pattern, amoxicillin and metronidazole (AMR(R) MET(R)) was the most common (23.7%) amongst the isolates. More than 60% of the isolates exhibited multi-drug resistance to three or four antibiotics.

CONCLUSION

Multi-drug resistance is common against the current treatment regimen in Cameroon and, therefore, calls for urgent studies involving newer and broad spectrum antibiotics to address the problem.

Mechanism of IS200/IS605 family DNA transposases: activation and transposon-directed target site selection

The smallest known DNA transposases are those from the IS200/IS605 family. Here we show how the interplay of protein and DNA activates TnpA, the Helicobacter pylori IS608 transposase, for catalysis. First, transposon end binding causes a conformational change that aligns catalytically important protein residues within the active site. Subsequent precise cleavage at the left and right ends, the steps that liberate the transposon from its donor site, does not involve a site-specific DNA-binding domain. Rather, cleavage site recognition occurs by complementary base pairing with a TnpA-bound subterminal transposon DNA segment. Thus, the enzyme active site is constructed from elements of both protein and DNA, reminiscent of the interdependence of protein and RNA in the ribosome. Our structural results explain why the transposon ends are asymmetric and how the transposon selects a target site for integration, and they allow us to propose a molecular model for the entire transposition reaction.

High prevalence and level of resistance to metronidazole, but lack of resistance to other antimicrobials in Helicobacter pylori, isolated from a multiracial population in Kuwait

BACKGROUND

The primary treatment regimen for Helicobacter pylori infection for Kuwaitis does not contain metronidazole, but that for expatriates does. There is also increasing failure of antimicrobial therapy.

AIM

To determine the susceptibility of H. pylori from upper gastrointestinal biopsies of Kuwaitis and non-Kuwaitis to find out if differences existed in the susceptibilities of the isolates from the two different populations.

METHODS

The susceptibilities of 96 H. pylori isolates were tested against metronidazole, amoxicillin, clarithromycin and tetracycline by the E test. The rdxA gene was analysed from selected metronidazole-susceptible and metronidazole-resistant strains to find out polymorphism and the basis of metronidazole resistance.

RESULTS

Approximately, 70% of isolates from both populations were metronidazole resistant with 65% isolates showing high minimum inhibitory concentration values of >256 mug/mL. No resistance to the other three antimicrobials was found. There were novel nonsense and missense mutations with no deletion in the rdxA gene by insertion of mini-IS605.

CONCLUSIONS

The prevalence and level of metronidazole resistance in H. pylori in the two populations was high with no difference, in spite of different treatment regimens. Metronidazole resistance in this transitional country appeared to be independent of prior metronidazole use for treatment of H. pylori infection.

Alterations in rdxA and frxA genes and their upstream regions in metronidazole-resistant Helicobacter pylori isolates

Metronidazole resistance among Helicobacter pylori strains has been related to alterations in gene products having metronidazole nitroreductase activities. RdxA and FrxA proteins are the two major contributing factors. In this investigation, the rdxA and frxA genes and their upstream regions were analyzed in 19 H. pylori isolates, 8 of which were metronidazole-sensitive (MIC < or = 8 microg/mL) and 11 of which were metronidazole-resistant (MIC > or = 8 microg/mL), as determined by the E-test. Among the metronidazole-resistant isolates, three contained both RdxA and FrxA proteins with premature truncation caused by gene nonsense mutations or frameshift mutations, while three contained only stop mutations in FrxA and two only in RdxA. Substitutions of amino acids occurred in other RdxA (5/6) and FrxA (4/5) proteins from metronidazole resistant isolates as compared with those from metronidazole-sensitive ones. All metronidazole-resistant isolates had alterations in RdxA and/or FrxA proteins. Moreover, the upstream regions (-1 to -35) of rdxA and frxA genes in some metronidazole-resistant isolates varied by nucleotide insertion and/or deletion or substitution. The patterns of variation in both genes and their upstream regions were highly diversified. Alterations in rdxA and frxA genes and their upstream regions may be involved in the development of metronidazole resistance in H. pylori.

Cell elongation and cell death of helicobacter pylori is modulated by the disruption of cdrA (cell division-related gene A)

The cell division-related gene A (cdrA) of Helicobacter pylori is dispensable in vivo and unique in having a repressive role on cell division and long-term survival. To clarify its role, comparisons of the wildtype HPK5 and isogenic cdrA-disrupted mutant HPKT510 were examined by ultrastructural morphology, PBP profiles, and susceptibility to beta-lactam antibiotics during long-term cultivation. Ultrastructural analyses revealed that the shorter rods of HPKT510 had a slightly wider periplasmic space between the inner and the outer membrane than those of HPK5. Cell division of HPKT510 cells was complete even under high-salt conditions in which HPK5 cells became filamentous due to inhibition of division. The filamentous HPK5 cells constructed an inner membrane without a cell wall at the presumed division site. After 4 days of cultivation (the late stationary phase), most of the HPK5 cells turned into ghosts and aggregates, while some of the HPKT510 cells remained as curved rods, which coincided with the results of cell viability. HPKT510 cells became resistant to ampicillin killing compared to HPK5 cells, although their minimum inhibitory concentrations (MICs) and PBP profiles were not significantly different. These results suggest that the cdrA product represses cell division via inhibiting cell wall synthesis at division site. During infection in both mice and humans, inactivation of cdrA eventually gains biological aspects such as increased viability, long-term survival and tolerance to antibiotics and high-salt condition, which might enhance a persistent infection.

Helicobacter pylori antibiotic resistance in Iran

AIM: To examine the frequency of antibiotic resistance in Iranian Helicobacter pylori (H pylori) strains isolated from two major hospitals in Tehran.

METHODS: Examination of antibiotic resistance was performed on 120 strains by modified disc diffusion test and PCR-RFLP methods. In addition, in order to identify the possible causes of the therapeutic failure in Iran, we also determined the resistance of these strains to the most commonly used antibiotics (metronidazole, amoxicillin, and tetracycline) by modified disc diffusion test.

RESULTS: According to modified disc diffusion test, 1.6% of the studied strains were resistant to amoxicillin, 16.7% to clarithromycin, 57.5% to metronidazole, and there was no resistance to tetracycline. Of the clarithromycin resistant strains, 73.68% had the A2143G mutation in the 23S rRNA gene, 21.05% A2142C, and 5.26% A2142G. None of the sensitive strains were positive for any of the three point mutations. Of the metronidazole resistant strains, deletion in rdxA gene was studied and detected in only 6 (5%) of the antibiogram-based resistant strains. None of the metronidazole sensitive strains possessed rdxAgene deletion.

CONCLUSION: These data show that despite the fact that clarithromycin has not yet been introduced to the Iranian drug market as a generic drug, nearly 20% rate of resistance alerts toward the frequency of macrolide resistance strains, which may be due to the widespread prescription of erythromycin in Iran. rdxA gene inactivation, if present in Iranian H pylori strains, may be due to other genetic defects rather than gene deletion.

Restriction of DNA encoding selectable markers decreases the transformation efficiency of Helicobacter pylori

Helicobacter pylori populations recovered from the human stomach display extensive recombination and quasispecies development, and this suggests frequent exchange of DNA between different strains in vivo. In vitro, however, most H. pylori strains display restriction to the uptake of non-self DNA, as measured using selectable markers, regardless of their competency for transformation with self DNA. We have examined the effect of different selectable markers on double-crossover recombination efficiencies in three reference strains (1061, 26695 & SS1) and one clinical isolate (CHP1) of H. pylori. All strains were efficiently transformable to kanamycin or chloramphenicol resistance by using self-genomic DNA from isogenic mutants bearing the aphA3 or cat cassettes, respectively. However, strains 26695 and CHP1 showed a 3-5-log reduction in transformation efficiency by non-self recombinant DNA containing aphA3, when compared to cat. Strain 1061 readily accepted either cassette, and strain SS1 was poorly tolerant of any non-self DNA. Genome-wide random mutagenesis of these strains was only achievable with a selectable marker that allowed high transformation efficiency. Digestion of 32P-labelled cassettes by H. pylori lysates mirrored the transformation results and indicated that in some strains these cassettes are the targets of enzymatic restriction.

Helicobacter pyloridisulphide 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.

Molecular biology methods for the characterization of Helicobacter pylori infections and their diagnosis

Helicobacter pylori infects approximately half of the human population; however, the outcome of infection is affected by many factors, including strain and host genotype characteristics and bacterial density within the stomach. Many molecular methods have been developed to provide information with respect to these characteristics. Methods that provide results within 24 h of endoscopy may be used to develop individualized treatment that is more effective, results in fewer side effects, cuts costs,decreases the number of treatment failures and results in the development of fewer antibiotic-resistant H. pylori strains.

Role of the rdxA and frxA genes in oxygen-dependent metronidazole resistance of Helicobacter pylori

Almost 50 % of all Helicobacter pylori isolates are resistant to metronidazole, which reduces the efficacy of metronidazole-containing regimens, but does not make them completely ineffective. This discrepancy between in vitro metronidazole resistance and treatment outcome may partially be explained by changes in oxygen pressure in the gastric environment, as metronidazole-resistant (MtzR) H. pylori isolates become metronidazole-susceptible (MtzS) under low oxygen conditions in vitro. In H. pylori the rdxA and frxA genes encode reductases which are required for the activation of metronidazole, and inactivation of these genes results in metronidazole resistance. Here the role of inactivating mutations in these genes on the reversibility of metronidazole resistance under low oxygen conditions is established. Clinical H. pylori isolates containing mutations resulting in a truncated RdxA and/or FrxA protein were selected and incubated under anaerobic conditions, and the effect of these conditions on the MICs of metronidazole, amoxycillin, clarithromycin and tetracycline, and cell viability were determined. While anaerobiosis had no effect on amoxycillin, clarithromycin and tetracycline resistance, all isolates lost their metronidazole resistance when cultured under anaerobic conditions. This loss of metronidazole resistance also occurred in the presence of the protein synthesis inhibitor chloramphenicol. Thus, factor(s) that activate metronidazole under low oxygen tension are not specifically induced by low oxygen conditions, but are already present under microaerophilic conditions. As there were no significant differences in cell viability between the clinical isolates, it is likely that neither the rdxA nor the frxA gene participates in the reversibility of metronidazole resistance.

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.

Development of an interleukin-12-deficient mouse model that is permissive for colonization by a motile KE26695 strain of Helicobacter pylori

The identification of genes associated with colonization and persistence of Helicobacter pylori in the gastric mucosa has been limited by the lack of robust animal models that support infection by strains whose genomes have been completely sequenced. Here we report that an interleukin-12 (IL-12)-deficient mouse (IL-12(-/-) p40 subunit knockout in C57BL/6 mouse) is permissive for infection by a motile variant (KE88-3887) of The Institute For Genomic Research-sequenced strain (KE26695) of H. pylori. The IL-12-deficient mouse was also more permissive for colonization by the mouse-colonizing Sydney 1 strain of H. pylori than were wild-type C57BL/6 mice. Differences in colonization efficiency were demonstrated by mouse challenge with SS1 strains containing loss-of-function mutations in two genes (hspR and hrcA), whose products negatively regulate several heat shock genes. At 5 weeks postinfection, double-knockout mutants (SS1 hspR hrcA) efficiently colonized IL-12-deficient mice (5 of 5 animals compared to 4 of 10 for C57BL6 mice) and bacterial counts were higher in stomachs of IL-12-deficient mice (10(6) versus 10(5) CFU/g of stomach, respectively). IL-12-deficient mice were efficiently colonized by KE88-3887 (29 of 30), but not by nonmotile KE26695, and bacterial numbers (10(4) to 10(5) CFU/g of stomach) were unchanged over an 8-week period postinfection. In contrast, C57BL/6 mice were inefficiently colonized by KE88-3887 (8 of 20 animals with bacterial loads at the limit of detection, approximately 10(3) CFU/g), and infection did not persist much beyond 5 weeks. Cytokine responses (tumor necrosis factor alpha and gamma interferon), pathology, and antral-predominant infection were indistinguishable between IL-12-deficient and C57BL/6 mice. The increased permissiveness of the IL-12-deficient mouse for infection with H. pylori should facilitate whole-genome-based strategies to study genes associated with virulence and immune modulation.

Characterization of the genes rdxA and frxA involved in metronidazole resistance in Helicobacter pylori

Metronidazole (Mtz) resistance in Helicobacter pylori has been found to be associated with mutations in rdxA, a gene encoding an oxygen-insensitive NADPH nitroreductase, and enhanced by mutations in frxA, a gene encoding a NAD(P)H-flavin oxidoreductase. The roles of these two genes in Mtz resistance in H. pylori were examined in this study. The rdxA and frxA genes were sequenced in nine pairs of strains isolated from biopsies obtained from patients before and after failed eradication treatments which included Mtz and resulted in the appearance of resistant strains. Metronidazole resistance could be explained in seven of these pairs of strains by mutations in rdxA and frxA. However, in one pair of strains, rdxA was identical in the susceptible and resistant strains, and only changes in frxA were observed; and in another pair, neither rdxA nor frxA were different in the susceptible and resistant strains. Sequencing of the upstream region of frxA and of the recA gene in the latter pair of strains did not reveal any mutations. To establish whether mutations in frxA alone could be involved in Mtz resistance, a resistant Escherichia coli strain transformed with the frxA of a Mtz susceptible H. pylori strain was rendered susceptible, and transformation with a mutated H. pylori frxA gene under the same conditions did not change the resistant E. coli phenotype. The results suggested that a Mtz resistance phenotype may arise in H. pylori without mutations in rdxA or frxA, or with mutations only in frxA.

Mechanism and clinical significance of metronidazole resistance in Helicobacter pylori

Metronidazole was introduced in 1959 for the treatment of Trichomonas vaginalis, but was subsequently shown to be active against anaerobic and some micro-aerophilic bacteria as well. In anaerobic microorganisms with their low redox potential, metronidazole is reduced to its active metabolite by a one-electron transfer step. Metronidazole is often used in treatment regimens for Helicobacter pylori, a microaerophilic bacterium, but resistance to this drug is frequently encountered. The metabolism of metronidazole in H. pylori must differ from that in anaerobic bacteria as metabolites formed by a one-electron transfer are readily re-oxidized in the micro-aerophilic environment of H. pylori. This process is called 'futile cycling' and is accompanied by the formation of toxic oxygen radicals that are neutralized by an active scavenger system. Recently, it has been shown that in H. pylori, in contrast to the situation in anaerobes, an oxygen-insensitive nitroreductase. encoded by the rdxA gene, is responsible for the activation of metronidazole. Activation by this enzyme is by a two-electron transfer step, preventing futile cycling' and thereby enabling the activation of metronidazole in a micro-aerophilic environment. Metronidazole resistance has been shown to be associated with null mutations in the rdxA gene in most clinical isolates. However, there may be some 'background metronidazole susceptibility' in metronidazole-resistant strains caused by other (oxygen-sensitive) nitroreductases. Recently, three meta-analyses of the impact of metronidazole resistance on treatment efficacy have all shown a significant reduction in efficacy of metronidazole containing regimens in patients infected with a resistant strain. The impact of resistance proved to be dependent on the other components of the regimen and on treatment duration.

Antibiotic resistance of Helicobacter pylori strains in Japanese children

The resistance of Helicobacter pylori to the recently available antibiotic treatment regimens has been a growing problem. We investigated the prevalence of H. pylori resistance to clarithromycin, metronidazole, and amoxicillin among 51 H. pylori isolates from Japanese children. In addition, the mutations of the corresponding gene were studied by PCR and restriction fragment length polymorphism analysis. Primary resistance to clarithromycin, metronidazole, and amoxicillin was detected in 29, 24, and 0% of strains, respectively. The eradication rates in clarithromycin-susceptible and -resistant strains were 89 and 56%, respectively (P < 0.05). The prevalence of strains with acquired resistance to clarithromycin (78%) was higher than that of strains with primary resistance (P < 0.01). Among the clarithromycin-resistant strains studied, 92% showed cross-resistance to azithromycin. No acquired resistance to amoxicillin was demonstrated. The A2144G mutation in the 23S rRNA gene was detected in 11 of 12 (92%) clarithromycin-resistant strains tested, whereas the mutation was not detected in any of the 15 susceptible strains. The deletion of the rdxA gene was not demonstrated in any of the strains. The results indicate that a high prevalence of clarithromycin-resistant strains is associated with eradication failure. Testing of susceptibility to clarithromycin is recommended.

Metronidazole resistance in Helicobacter pylori

Modern triple drug regimens are highly effective for treating Helicobacter pylori infection, but bacterial resistance to one of the most effective antibiotics, metronidazole, is a serious and increasing problem. The activity of metronidazole in H. pylori is dependent on reduction of its nitro moiety to highly reactive compounds that cause DNA strand breakage. The acquisition of resistance is highly associated with mutational inactivation of the rdxA gene, which encodes an oxygen-insensitive NADPH nitroreductase. Recent evidence has suggested that inactivation of frxA (NADPH flavin oxidoreductase), fdxB (ferredoxin-like protein) and possibly other reductase-encoding genes may also contribute to the resistant phenotype. Improved understanding of the mechanisms of metronidazole resistance in H. pylori is essential for the development and validation of biopsy-based tests for detection of resistance in clinical practice.

Differentiation of metronidazole-sensitive and -resistant clinical isolates of Helicobacter pylori by immunoblotting with antisera to the RdxA protein

Antimicrobial resistance in Helicobacter pylori is a serious and increasing problem, and the development of rapid, reliable methods for detecting resistance would greatly improve the selection of antibiotics used to treat gastric infection with this organism. We assessed whether detection of the RdxA protein could provide the basis for determining the susceptibility of H. pylori to metronidazole. In order to raise polyclonal antisera to RdxA, we cloned the rdxA gene from H. pylori strain 26695 into the commercial expression vector pMAL-c2, purified the resultant fusion protein by affinity chromatography, and used this recombinant RdxA preparation to immunize rabbits. We then used this specific anti-RdxA antibody to perform immunoblotting on whole bacterial cell lysates of 17 metronidazole-sensitive and 27 metronidazole-resistant clinical isolates of H. pylori. While a 24-kDa immunoreactive band corresponding to the RdxA protein was observed in all metronidazole-sensitive strains, this band was absent in 25 of 27 resistant isolates. Our results indicate that testing for the absence of the RdxA protein would identify the majority of clinical isolates that will respond poorly to metronidazole-containing eradication regimens and have implications for the development of assays capable of detecting metronidazole resistance in H. pylori.

DNA sequence analysis of rdxA and frxA from 12 pairs of metronidazole-sensitive and -resistant clinical Helicobacter pylori isolates

We previously reported that inactivation of rdxA and/or frxA converted Helicobacter pylori from metronidazole sensitive to metronidazole resistant. To examine the individual roles of rdxA and frxA in the development of metronidazole resistance in H. pylori, we examined the status of rdxA and frxA from 12 pairs of metronidazole-sensitive and -resistant H. pylori isolates obtained following unsuccessful therapy containing metronidazole. Arbitrary primed fingerprinting analyses revealed that the genotypes of 11 sensitive and resistant pairs of strains were essentially identical. Amino acid sequence identities of RdxA and FrxA from the 14 metronidazole-sensitive isolates ranged from 92 to 98% and 95 to 98%, respectively, compared to that of H. pylori J99 (MIC, 1 microg/ml). All strains with high-level metronidazole resistance (MICs, 128 microg/ml) contained premature truncation of both RdxA and FrxA caused by nonsense and/or frameshift mutations. Strains with intermediate resistance to metronidazole (MICs, 32 to 64 microg/ml) contained a single premature truncation and/or altered RdxA and FrxA caused by nonsense, frameshift, and unique missense mutations. The low-level metronidazole-resistant strains (MICs, 8 microg/ml) contained unique missense mutations in FrxA but no specific changes in RdxA. The results demonstrate that alterations in both the rdxA and frxA genes are required for moderate and high-level metronidazole resistance and that metronidazole resistance that develops during anti-H. pylori therapy containing metronidazole is most likely to involve a single sensitive strain infection rather than a coinfection with a metronidazole-resistant strain.

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.