Helicobacter pylori isolates from ethnic minority patients in Guangxi:Resistance rates,mechanisms,and genotype

AIM:To investigate the rate of Helicobacter pylori（H.pylori）resistance to clarithromycin among ethnic minority patients in Guangxi,explore the underlyingmechanisms,and analyze factors influencing genotype distribution of H.pylori isolates.METHODS:H.pylori strains were isolated,cultured and subjected to drug sensitivity testing.The 23S rRNA gene of H.pylori isolates was amplified by PCR and analyzed by PCR-RFLP and direct sequencing to detect point mutations.REP-PCR was used for genotyping of H.pylori isolates,and NTsys₂ software was used for clustering analysis based on REP-PCR DNA fingerprints.Factors potentially influencing genotype distribution of H.pylori isolates were analyzed.RESULTS:The rate of clarithromycin resistance was31.3%.A2143G and A2144G mutations were detected in the 23S rRNA gene of all clarithromycin-resistant H.pylori isolates.At a genetic distance of 78%,clarithromycin-resistant H.pylori isolates could be divided into six groups.Significant clustering was noted among H.pylori isolates from patients with peptic ulcer or gastritis.CONCLUSION:The rate of clarithromycin resistance is relatively high in ethnic minority patients in Guangxi.Main mechanisms of clarithromycin resistance are A2143G and A2144G mutations in the 23S rRNA gene.Clarithromycin-resistant H.pylori isolates can be divided into six groups based on REP-PCR DNA fingerprints.Several factors such as disease type may influence the genotype distribution of H.pylori isolates.     

Five-year sequential changes in secondary antibiotic resistance of Helicobacter pylori in Taiwan

AIM: To determine changes in the antibiotic resistance of Helicobacter pylori(H. pylori) in southern Taiwan after failure of first-line standard triple therapy.METHODS: We analyzed 137 H. pylori-infected isolates from patients who experienced eradication failure after standard first-line triple therapy from January2010 to December 2014. The H. pylori strains were tested for susceptibility to amoxicillin, clarithromycin,levofloxacin, metronidazole and tetracycline using the E-test method. The minimal inhibitory concentration(MIC) was determined by the agar dilution test.MIC values of ≥ 0.5, ≥ 1, ≥ 1, ≥ 4 and ≥ 8 mg/L were considered to be the resistance breakpoints for amoxicillin, clarithromycin, levofloxacin, tetracycline and metronidazole, respectively.RESULTS: A high resistance rate was found for clarithromycin(65%-75%) and metronidazole(30%-40%)among patients who failed first-line standard therapy.The resistance levels to amoxicillin and tetracycline remained very low; however, levofloxacin resistance was as high as 37.5% in 2010 but did not increase any further during the past 5 years. The rates of resistance to these antibiotics did not show a statistically significant upward or downward trend.CONCLUSION: Antibiotic resistance of H. pylori remains a problem for the effective eradication of this pathogen and its associated diseases in Taiwan. High clarithromycin resistance indicated that this antibiotic should not be prescribed as a second-line H. pylori eradication therapy. Moreover, levofloxacin-based second-line therapy should be used cautiously, and the local resistance rates should be carefully monitored.     

Attempts to enhance the eradication rate of helicobacter pylori infection

Increasing rates of antimicrobial resistance to clarithromycin and metronidazole present challenges in maintaining optimal eradication rates.Knowledge of local antibiotic resistance and consumption pattern is important in selecting a reliable regimen.In addition,adverse effect profiles of therapeutic regimens are important and must be addressed to enhance compliance rates.Various methods of enhancing the eradication rates of Helicobacter pylori(H.pylori)have been investigated,including changing combinations or durations of established drugs,adding adjuvant drugs,or development of new molecules or agents.Bismuth-containing quadruple,sequential,concomitant,and levofloxacin-based triple therapies are replacing the long-standing standard of the triple regimen.Despite the encouraging results of these regimens,individualized approaches like treatment after antibiotics resistance test or CYP2C19genotyping would be the mainstream of future therapy.Because scientific,economic,and technical problems make these advance therapies unfit for widespread use,future development for H.pylori therapy should be directed to overcome individualized antibiotic resistance.Although various novel regimens and additive agents have indicated favorable outcomes,more studies or validations are needed to become a mainstream H.pylori therapy.     

Characterization of clarithromycin resistance in Malaysian isolates of Helicobacterpylori

AIM： To characterize the types of mutations present in the 23S rRNA genes of Malaysian isolates of clarithromycin-resistant Helicobacter pylori （H pylorl~. METHODS： Clarithromycin susceptibility of H pylori isolates was determined by E test. Analyses for point mutations in the domain V of 23S rRNA genes in clarithromycin-resistant and -sensitive strains were performed by sequence analysis of amplified polymerase chain reaction products. Restriction fragment length polymorphism was performed using Bsa I and MboI enzymes to detect restriction sites that correspond to the mutations in the clarithromycin- resistant strains. RESULTS： Of 187 isolates from 120 patients, four were resistant to clarithromycin, while 183 were sensitive. The MIC of the resistant strains ranged from 1.5 to 24 pg/mL. Two isolates had an A2142G mutation and another two had A2143G mutations. A T2182C mutation was detected in two out of four clarithromycin-resistant isolates and in 13 of 14 clarithromycin-sensitive isolates. Restriction enzyme analyses with Bsa I and Mbo I were able to detect the mutations. CONCLUSION： Clarithromycin resistance is an uncommon occurrence among Malaysian isolates of Hpylori strains and the mutations A2142G and A2143G detected were associated with low-level resistance.     

Antibiotics resistance rate of Helicobacter pylori in Bhutan

AIM:To survey the antibiotic resistance pattern of Helicobacter pylori(H.pylori)strains isolated from Bhutanese population.METHODS:We isolated 111 H.pylori strains from the gastric mucosa of H.pylori-infected patients in Bhutan in 2010.The Epsilometer test was used to determine the minimum inhibitory concentrations(MICs)of amoxicillin(AMX),clarithromycin(CLR),metronidazole(MNZ),levofloxacin(LVX),ciprofloxacin(CIP),and tetracycline(TET).RESULTS:Nineteen of the isolated H.pylori strains were susceptible to all antibiotics tested.The isolated strains showed the highest rate of antibiotic resistance to MNZ(92/111,82.9%).Among the 92 MNZresistant strains,74 strains(80.4%)showed high-level resistance(MIC≥256 g/mL).Three strains were resistance to LVX(2.7%).These strains were also resistance to CIP.None of the strains showed resistance to CLR,AMX and TET.CONCLUSION:CLR-based triple therapy is a more effective treatment approach over MNZ-based triple therapy for H.pylori infection in Bhutan.     

Optimal treatment strategy for Helicobacter pylori:Era of antibiotic resistance

Standard triple therapy,consisting of a proton pump inhibitor,plus amoxicillin and clarithromycin,has been the most commonly used first-line treatment regimen for Helicobacter pylori(H.pylori)eradication for many years worldwide.However,as a result of increased resistance to antibiotics,H.pylori eradication rates with use of standard triple therapy have been declining and recently reached<80%in many countries.Several new strategies to enhance the eradication rate of H.pylori have been studied.Currently,among the alternative first-line eradication regimens,concomitant and hybrid regimens have shown excellent results and could be the optimal treatment option.Although clinical usefulness of rescue therapy for patients in whom eradication of H.pylori with non-bismuth quadruple regimen has failed is unclear,levofloxacin-based quadruple therapy has shown promise as a rescue treatment.The choice of third-line therapy depends on factors such as the local pattern of antibiotic resistance,drug availability,and previous treatment.We hope that a simple method for detection of antibiotic susceptibility using polymerase chain reaction would be a possible alternative to administration of"tailored treatment"in the era of increasing prevalence of antimicrobial resistance.     

Eradication of Helicobacter pylori infection: Which regimen first?

Helicobacter pylori(H.pylori)is a well-known human pathogen that plays an essential role in the pathogenesis of chronic gastritis,peptic ulcer disease,and gastric malignancies.Although H.pylori is susceptible to several antimicrobials,this infection has proven challenging to cure because of the increasing prevalence of bacterial strains that are resistant to the most commonly used antimicrobials,particularly clarithromycin.An effective(i.e.,>90%)first-line therapy is mandatory for avoiding supplementary treatments and testing,and more importantly for preventing the development of secondary resistance.This study reviews the recent literature on first-line therapies forH.pylori.The eradication rates following standard triple therapy(a proton pump inhibitor plus amoxicillin and clarithromycin)for H.pylori infection are declining worldwide.Several first-line strategies have been proposed to increase the eradication rate,including extending the treatment duration to 14 d,the use of a four-drug regimen(bismuth-containing quadruple,sequential,and concomitant treatments),and the use of novel antibiotics,such as fluoroquinolones.However,the ef5ficacy of these regimens is controversial.A first-line eradication regimen should be based on what works best in a defined geographical area and must take into account the prevalence of antimicrobial resistance in that region.     

Punctual mutations in 23S rRNA gene of clarithromycinresistant Helicobacter pylori in Colombian populations

AIM To characterize punctual mutations in 23S rRNA gene of clarithromycin-resistant Helicobacter pylori(H. pylori) and determine their association with therapeutic failure.METHODS PCR products of 23S rRNA gene V domain of 74 H. pylori isolates; 34 resistant to clarithromycin(29 from a low-risk gastric cancer(GC) population: TumacoColombia, and 5 from a high-risk population: TuquerresColombia) and 40 from a susceptible population(28 from Tumaco and 12 from Túquerres) were sequenced using capillary electrophoresis. The concordance between mutations of V domain 23S rRNA gene of H. pylori and therapeutic failure was determined using the Kappa coefficient and Mc Nemar's test was performed to determine the relationship between H. pylori mutationsand clarithromycin resistance.RESULTS23S rRNA gene from H. pylori was amplified in 56/74 isolates, of which 25 were resistant to clarithromycin(20 from Tumaco and 5 from Túquerres, respectively). In 17 resistant isolates(13 from Tumaco and 4 from Túquerres) the following mutations were found: A1593 T1, A1653 G2, C1770 T, C1954 T1, and G1827 C in isolates from Tumaco, and A2144 G from Túquerres. The mutations T2183 C, A2144 G and C2196 T in H. pylori isolates resistant to clarithromycin from Colombia are reported for the first time. No association between the H. pylori mutations and in vitro clarithromycin resistance was found. However, therapeutic failure of eradication treatment was associated with mutations of 23S rRNA gene in clarithromycin-resistant H. pylori(κ = 0.71).CONCLUSION The therapeutic failure of eradication treatment in the two populations from Colombia was associated with mutations of the 23S rRNA gene in clarithromycinresistant H. pylori.     

Seven-day triple therapy is a better choice for Helicobacter pylori eradication in regions with low antibiotic resistance

AIM: To investigate whether 7-d triple therapies are still valid in populations with low levels of resistance.METHODS: A total of 1106 Helicobacter pylori(H. pylori)-positive patients were divided into three groups,each of which received one type of 7-d triple therapy. Therapeutic outcomes of the patients were assessed by the 13C-urea breath test at 8 wk after treatment. The susceptibility of H. pylori to antibiotics was determined by an agar-dilution method. Data analysis was performed by χ2 tests.RESULTS: The eradication rates in groups A,B and C were 90.71%(332/366),90.46%(313/346) and 90.87%(189/208),respectively(P = 0.986). The resistance rates were 8.91% for clarithromycin,14.78% for levofloxacin and 0% for amoxicillin. The eradication rate was significantly different between clarithromycin-and levofloxacin-resistant patients(P 0.05) in group A. Patients whose treatment failed in group A also had a higher clarithromycin resistance rate than did successive patients(P = 0.034). However,levofloxacin resistance had no obvious influence on the eradication rate. Furthermore,three main antibiotics(clarithromycin,levofloxacin and amoxicillin) had lower DID(defined daily dose per 1000 inhabitants per day) in this city.CONCLUSION: Clarithromycin resistance is the main reason for the failure of 7-d triple therapy. In populations with low levels of resistance,a 7-d triple therapy is a viable choice. The choice of therapy should not be influenced by conditions in high antibiotic resistance regions.     

Antimicrobial susceptibility of Helicobacter pylori strains isolated from patients in Shiraz, Southern Iran

AIM: To improve our understanding of Iranian regional variation in Helicobacter pylori (H. pylori ) antibiotic resistance rates to find the best antibiotic therapy for eradication of H. pylori infections.METHODS: A total of 266 patients undergoing endoscopy in Shiraz, Southern Iran, were included in this study. H. pylori strains were isolated from antral biopsies by culture and confirmed by the rapid urease-test and gram staining. Antibiotic susceptibility of H. pylori isolates was determined by E-test.RESULTS: A total of 121 H. pylori strains were isolated, 50 from male and 71 from female patients. Data showed that 44% (n = 53), 20% (n = 24), 5% (n = 6), and 3% (n = 4) of all strains were resistant to the antibiotics metronidazole, amoxicillin, clarithromycin, and tetracycline, respectively. When the antibiotics were considered together we found 11 sensitivity patterns for the strains. Resistance to metronidazole was significantly higher in female than in male patients (P < 0.05). In about 71% of the metronidazole-resistant isolates, the minimum inhibitory concentrations (MICs) exceeded 256 μg/mL.CONCLUSION: We found a moderate rate of primary resistance to metronidazole. However, a high MIC (> 256 mg/L) which was found in 71% of the isolates is considerable. In the case of amoxicillin, an increased resistance rate of 20% is worrying. Resistance to clarithromycin and tetracycline is also emerging among the H. pylori strains in our region.     

Clinical role and importance of fluorescence in situ hybridization method in diagnosis of H pylori infection and determination of clarithromycin resistance in H pylori eradication therapy

H pylori is etiologically associated with gastritis, gastric and duodenal ulcers, gastric adenocarcinoma and mucosa-associated lymphoid tissue （MALT） lymphoma. Eradicating H pylori may convert rapidly the outcome of related diseases with the use of more accurate diagnostic molecular tests. Indeed some of the tests cannot give the evidence of current infection; H pylori can be detected by noninvasive and invasive methods, the latter requiring an endoscopy. Eradication failure is a big problem in Hpylori infection. Recently, clarithromycin resistance in H pylori strains is increasing and eradication therapy of this bacterium is becoming more difficult. Molecular methods have frequently been applied besides phenotypic methods for susceptibility testing to detect clarithromycin resistance due to mutations in the 2143 and 2144 positions of 23S rRNA gene. Fluorescence in situ hybridization （FISH） method on paraffin embedded tissue is a rapid, accurate and cost-effective method for the detection of H pylori infection and to determine clarithromycin resistance within three hours according to the gold standards as a non-culture method. This method can also be applied to fresh biopsy samples and the isolated colonies from a culture of Hpylori, detecting both the culturable bacillary forms and the coccoid forms of Hpylori, besides the paraffin embedded tissue sections. This technique is helpful for determining the bacterial density and the results of treatment where clarithromycin has been widely used in populations to increase the efficacy of the treatment and to clarify the treatment failure in vitro.     

Treatment of Helicobacter pylori infection:Meeting the challenge of antimicrobial resistance

Treatment of Helicobacter pylori(H.pylori)infection is paramount for the management of prevalent gastrointestinal disorders including peptic ulcer disease and gastric cancer.Due to the wide increase in prevalence of H.pylori resistance to antibiotics,clarithromycin-based triple therapies are not any more suitable for unconditional empiric use,and should not be recommended,unless local resistance to this antibiotic is low(<20%).Alternative strategies have been proposed to overcome the issue of increasing clarithromycin resistance,and some of them are already implemented in clinical practice.These comprise:(1)adoption of novel,more effective,empirical treatments:bismuth quadruple,sequential,non-bismuth quadruple(concomitant),dual-concomitant(hybrid),and levofloxacin-based regimens,the latter mainly designated as second-line/rescue options;(2)perspectives for a susceptibility-guided(tailored)therapeutic approach based on culture-free molecular testing methods;and(3)adjunct use of probiotics to improve eradication rates.The present article is aimed to provide a comprehensive overview of current and emerging strategies in the treatment of H.pylori infection,focusing on the challenge of antimicrobial resistance.     

Helicobacter pylori:Management in 2013

Helicobacter pylori(H.pylori)is a prevalent,worldwide,chronic infection.Choice of treatment can be modified according to antibiotic-resistance rates of H.pylori.The ideal therapeutic regimen for H.pylori infection should achieve an eradication rate of≥80%.In some countries,triple therapy with a proton-pump inhibitor(PPI),clarithromycin,and amoxicillin or metronidazole is still the best option.Bismuth-containing quadruple therapy consisting of bismuth salts,tetracycline,metronidazole and PPI,may be the preferred option in countries with clarithromycin resistance>20%.Sequential therapy including a PPI and amoxicillin given for the first 5 d,followed by triple therapy including a PPI,clarithromycin,and nitroimidazole antimicrobial(all twice daily)for the remaining 5 d,can be another option for the first-line treatment of H.pylori.Recent data suggest that treatment with PPI,levofloxacin,and amoxicillin for 10 d is a good choice for second-line therapy.Concomitant therapy consisting of PPI,amoxicillin,clarithromycin and metronidazole is another option for second-line treatment.If second-line treatment also fails,it is recommended to culture H.pylori from biopsy specimens and perform antimicrobial susceptibility testing.Rescue treatment should be based on antimicrobial susceptibility.     

Treatment of Helicobacter pylori infection:Current status and future concepts

Helicobacter pylori(H.pylori)infection is highly associated with the occurrence of gastrointestinal diseases,including gastric inflammation,peptic ulcer,gastric cancer,and gastric mucosa-associated lymphoid-tissue lymphoma.Although alternative therapies,including phytomedicines and probiotics,have been used to improve eradication,current treatment still relies on a combination of antimicrobial agents,such as amoxicillin,clarithromycin,metronidazole,and levofloxacin,and antisecretory agents,such as proton pump inhibitors(PPIs).A standard triple therapy consisting of a PPI and two antibiotics(clarithromycin and amoxicillin/metronidazole)is widely used as the first-line regimen for treatment of infection,but the increased resistance of H.pylori to clarithromycin and metronidazole has significantly reduced the eradication rate using this therapy and bismuth-containing therapy or 10-d sequential therapy has therefore been proposed to replace standard triple therapy.Alternatively,levofloxacin-based triple therapy can be used as rescue therapy for H.pylori infection after failure of first-line therapy.The increase in resistance to antibiotics,including levofloxacin,may limit the applicability of such regimens.However,since resistance of H.pylori to amoxicillin is generally low,an optimized high dose dual therapy consisting of a PPI and amoxicillin can be an effective first-line or rescue therapy.In addition,the concomitant use of alternative medicine has the potential to provide additive or synergistic effects against H.pylori infection,though its efficacy needs to be verified in clinical studies.     

Development of Helicobacter pylori treatment: How do we manage antimicrobial resistance?

Helicobacter pylori(H. pylori) antimicrobial resistance is an urgent, global issue. In2017, the World Health Organization designated clarithromycin-resistant H.pylori as a high priority bacterium for antibiotic research and development. In addition to clarithromycin, resistance to metronidazole and fluoroquinolones has also increased worldwide. Recent international guidelines for management of H.pylori infection recommend bismuth or non-bismuth quadruple therapy for 14 d as a first-line treatment for H. pylori in areas of high clarithromycin and/or metronidazole resistance. Although these treatment regimens provide acceptable H. pylori eradication rates, the regimens used should not contribute to future resistance of H. pylori to antimicrobials. Moreover, these regimens can promote resistance, due to prolonged therapy with multiple antibiotics. A new strategy that can eradicate H. pylori as well as reduce the antibiotics used is required to prevent future antimicrobial resistance in H. pylori. Dual-therapy with vonoprazan and amoxicillin could be a breakthrough for H. pylori eradication in an era of growing antimicrobial resistance. This regimen may provide a satisfactory eradication rate of H. pylori and also minimize antimicrobial resistance due to single antibiotic use and the strong inhibitory effect of vonoprazan on gastric acid secretion.     

Current progress toward eradicating Helicobacter pylori in East Asian countries: Differences in the 2013 revised guidelines between China,Japan, and South Korea

New 2013 guidelines on Helicobacter pylori(H. pylori) infection have been published in China, Japan, and South Korea. Like the previous ones, these new guidelines differ between the three countries with regard to the indications for H. pylori eradication, diagnostic methods, and treatment regimens. The most profound change among all of the guidelines is that the Japanese national health insurance system now covers the expenses for all infected subjects up to second-line treatment. This makes the Japanese indications for eradication much wider than those in China and South Korea. With regard to the diagnosis, a serum H. pylori antibody test is not recommended in China, whereas it is considered to be the most reliable method in Japan. A decrease relative to the initial antibody titer of more than 50% after 6-12 mo is considered to be the most accurate method for determining successful eradication in Japan. In contrast, only the urea breath test is recommended after eradication in China, while either noninvasive or invasive methods(except the bacterial culture) are recommended in South Korea. Due to the increased rate of antibiotics resistance, first-line treatment is omitted in China and South Korea in cases of clarithromycin resistance. Notably, the Japanese regimen consists of a lower dose of antibiotics for a shorter duration(7 d) than in the other countries. There is neither 14 d nor bismuth-based regimen in the first-line and second-line treatment in Japan. Such differences among countries might be due to differences in the approvals granted by the governments and national health insurance system in each country. Further studies are required to achieve the best results in the diagnosis and treatment of H. pylori infection based on cost-effectiveness in East Asian countries.     

Different antibiotic susceptibility between antrum and corpus of the stomach,a possible reason for treatment failure of Helicobacter pylori infection

AIM:To assess whether antibiotic resistance varies between the antrum and corpus of the stomach of patients that are either Helicobacter pylori(H.pylori)therapy-naive or pre-treated.METHODS:H.pylori strains were isolated from antrum and corpus biopsies from 66 patients that received a diagnostic gastroduodenoscopy for variant clinical indications.Antimicrobial susceptibility to amoxicillin,clarithromycin,tetracycline,metronidazole,levofloxacin and rifabutin was tested with the E-test method on IsoSensitest agar with 10 vol%defibrinated horse blood.In patients with a different antibiotic susceptibility pattern between the isolates from the antrum and corpus,DNA fingerprinting via random amplified polymorphic DNA analysis was performed to detect differences among DNA patterns of H.pylori isolates.RESULTS:Primary,secondary and tertiary resistance to clarithromycin was 6.9%,53.8%and 83.3%,retrospectively.Metronidazole and levofloxacin resistance also increased according to the number of previous treatments(17.2%,69.2%,83.3%;13.8%,23.1%,33.3%).Tertiary resistance to rifabutin was detected in12.5%of patients.In none of the 66 patients a resistance against amoxicillin or tetracycline was detectable.Discordant antibiotic susceptibility between antrum and corpus isolates for different antibiotics was seen in 15.2%(10/66)of the patients.Two out of those ten patients were naive to any H.pylori antibiotic treatment.The remaining eight patients previously received at least one eradication therapy.DNA fingerprinting analysis revealed no substantial differences among DNA patterns between antrum and corpus isolates in the majority of patients suggesting an infection with a single H.pylori strain.CONCLUSION:Different antibiotic susceptibility between antrum and corpus biopsies is a common phenomenon and a possible explanation for treatment failure.Resistant H.pylori strains may be missed if just one biopsy from one anatomic site of the stomach is taken for H.pylori susceptibility testing.     

Pseudomembranous colitis associated with a triple therapy for Helicobacter pylori eradication

Helicobacter pylori(H.pylori)is one of the most common chronic bacterial infections in humans,affecting half of world’s population.Therapy for H.pylori infection has proven to be both effective and safe.The oneweek triple therapy including proton pump inhibitor,clarithromycin,and amoxicillin or metronidazole is still recommended as a first-line treatment to eradicate H.pylori infection in countries with low clarithromycin resistance.Generally,this therapy is well-tolerated,with only a few and usually minor side effects.However,rare but severe adverse effects such as pseudomembranous colitis have been reported,Clostridium difficile(C.difficile)infection being the main causative factor in all cases.We report the cases of two women who developed pseudomembranous colitis after a 1-wk triple therapy consisting of pantoprazole 20 mg bid,clarithromycin 500 mg bid,and amoxicillin 1 g bid to eradicate H.pylori infection.A limited colonoscopy showed typical appearance of pseudomembranous colitis,and the stool test for C.difficile toxins was positive.Rapid resolution of symptoms and negative C.difficile toxins were obtained in both patients with oral vancomycin.No relapse occurred during a four and eleven-month,respectively,follow up.These cases suggest that physicians should have a high index of suspicion for pseudomembranous colitis when evaluate patients with diarrhea following H.pylori eradication therapy.     

Detection of genotypic clarithromycin-resistant Helicobacter pylori by string tests

AIM:To evaluate the utility of the string test to detect genotypic clarithromycin-resistant Helicobacter pylori (H.pylori)by polymerase chain reaction(PCR)-restriction fragment length polymorphism.METHODS:Patients undergoing endoscopic examinations were enrolled in the present study.String tests were done on the next day of endoscopy.Segments of 23S rRNA were amplified from DNA obtained from string tests.PCR-restriction fragment length polymorphism was accomplished by restriction enzymes BbsI and BsaI recognizing the mutation site A to G at 2143or at 2142 of 23S rRNA domain V,respectively.RESULTS:One hundred and thirty-four patients with H.pylori infection underwent string tests.To compare phenotypic resistance,43 isolates were successfully cultured in 79 patients in whom 23S rRNA was successfully amplified.Of five patients with clarithromycinresistant H.pylori,23S rRNA of H.pylori isolates from four patients could be digested by BsaI.In 38 susceptible isolates,23S rRNA of H.pylori isolates from 36 patients could not be digested by either BsaI or BbsI.The sensitivity and specificity of the string test to detect genotypic clarithromycin resistance were 66.7%and97.3%,respectively.Positive and negative predictive values were 80%and 94.7%,respectively.CONCLUSION:String test with molecular analysis is a less invasive method to detect genotypic resistance before treatment.Further large-scale investigations are necessary to confirm our results.