| Background and ObjectiveHelicobacter pylori (Hp) is the pathogenic factor for chronic gastritis and peptic ulcers, and it is also related to the development of gastric carcinoma and the gastric mucosa-associated lymphoid tissue (MALT) lymphomas. In 1994, World Health Organization (WHO) classified Hp as a definite (class I ) carcinogen. American Center for Disease Control and Prevention (CDC) has classified Hp infectious disease as one of the new emerging infectious diseases.With the extensive application of antibiotics for the eradication of Hp treatment, the prevalences of Hp strains resistant to antibiotics raised sustainedly. Antibiotics resistance of Hp strains is the major reason for the defeated treatment. Since antibiotic is used differently in the different countries and regions, the resistance rate of Hp strains to antibiotic is also diverse. Therefore it is necessary to investigate the prevalences of antibiotic resistant Hp strains in order to provide information for the treatment of Hp infection.In the present study we attempted to investigate the rates of Hp strains resistant to amoxiclillin, clarithromycin, metronidazole and furaltadone in our hospital, and to explore the potential mechanism of Hp resistant to clarithromycin.Materials and methods (1). Isolation and identification of Hp strains: gastric mucosal biopsy specimens were obtained with routine gastroscopy, and then daubed on the culture plate. After incubation at 37℃under the micro-aerophilic conditions for 3 to 6 days, suspicious colonies were distinguished by typical colonial morphology and biochemical reactions. The positive colonies were subcultured and kept at -80℃.(2). Antibiotic resistance test :Hp strains was dissolved 6×10~7CFU/ml in distilled water, and then daubed on the medium, antibiotic susput the diffused plate on the medium. After incubation at 37℃under micro-aerophilic conditions for 5 days, the size of inhibition was measured.(3). DNA extraction: DNAs of the Hp strains collected from pure culture were extracted with the phenol-chloroform method and were kept in -20℃.(4): PCR-RFLP: the region of 23SrRNA containing A2142G and A2143G point was amplified by PCR method. PCR products of 300bp were obtained, and the products were digested with restriction endonuclease BbsI (A2142G)和BsaI (A2143G ) . The bands of PCR-RFLP patterns were analyzed.Results(1). The rates of 43 Hp strains resistant to amoxiclillin, clarithromycin, metronidazole and furaltadone were 9.3% (4/43), 18.6% (18/43), 53.5% (23/43) and 0%(0/43) respectively. The sums of Hp strains resistant to both clarithromycin and metronidazole were 5, to both amoxiclillin and metronidazole were 1, respectively.(2). DNAs from 7 of 8 Hp strains resistant to clarithromycin were digested with restriction endonuclease BsaI (A2143G) , and two bands with 200bp and 100bp were obtained respectively. The another DNA of Hp strains resistant to clarithromycin was digested with restriction endonuclease BsaI, a band with 300bp was obtained. DNAs from all eight clarithromycin-resistant Hp strains were digested with restriction endonuclease BbsI(A2142G), a band with 300bp was obtained; DNAs from 29 of 35 the clarithromycin- susceptive Hp strains were digested with restriction endonuclease BsaI and BbsI, and a band with 300bp was obtained in all these 29 strains. Conclusion(1). The resistant rate of Hp isolated in region to clarithromycin and amoxiclillin is high and to metronidazole is extremely high. No resistant strains are resistant to furazolidone in the present study. But there are Hp strains resistant to two sorts of antibiotic. These suggest that antibiotic should be selected rationally in the eradication of Hp strains treatment.(2). Clarithromycin resistance in Hp strains is associated with A2143G point mutation in 23SrRNA.
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