title: [Preliminary study on in-vitro induction of antibiotic resistance in Helicobacter pylori strains isolated from children].
abstract: OBJECTIVE
  Many clinical studies indicated that Helicobacter pylori (Hp) strains rarely acquired resistance to amoxicillin but easily to clarithromycin and metronidazole. However, it was unclear whether the antibiotic resistance of Hp strains was induced or passively selected during long-term or frequent treatment with metronidazole, clarithromycin and amoxicillin. To compare the propensity of acquired resistance to antibiotics, Hp strains were exposed to amoxicillin, clarithromycin and metronidazole in vitro in this study.
  
  
  METHODS
  All Hp strains were clinical isolates, derived from biopsy specimens of patients taken during endoscopy in the Affiliated Children's Hospital, Zhejiang University School of Medicine from December 2004 to July 2005. To seek susceptible strains, the minimum inhibitory concentrations (MICs) of the three antibiotics were determined by using Epsilometer test (E-test) method. In vitro induction was carried out on serially doubling concentrations of antibiotics incorporated into agar. Isolates were also transferred at least three times on antimicrobial agent-free medium, followed by a redetermination of the final MICs to assess the stability of the selected resistance.
  
  
  RESULTS
  7 strains were exposed to antibiotics in vitro. After 6 - 17 passages on antibiotic plates, 7 and 3 strains respectively acquired resistance to metronidazole and clarithromycin, while none of the strains were resistant to amoxicillin. The inductive folds were different among three groups: 8 - 128 folds in metronidazole group; 1 - 256 folds in clarithromycin group; 2 - 16 folds in amoxicillin group. After three transfers on antimicrobial agent-free medium, the MICs decreased significantly in amoxicillin group (P < 0.05) but had no change in metronidazole group and clarithromycin group (P > 0.05).
  
  
  CONCLUSIONS
  The metronidazole resistance in Hp was easily selected. Strains resistant to clarithromycin could be selected, but the amoxicillin resistance could not be selected after in vitro induction for Hp isolated from children. The correlation between in vitro and in vivo outcomes suggests that acquired resistance was the main cause for the resistance in Hp strains. The laboratory results of in vitro antibiotic induction could help predict the actual rate of resistance and select appropriate antibiotics for treatment.
authors.affiliation: Department of Gastroenterology, Children's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310003, China.
authors.forename: Wei-hui
authors.initials: WH
authors.lastname: Yan
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Hua-jian
authors.initials: HJ
authors.lastname: Hu
authors.forename: Jin-dan
authors.initials: JD
authors.lastname: Yu
authors.forename: Xiao-lei
authors.initials: XL
authors.lastname: Huang
authors.forename: Zhong-yue
authors.initials: ZY
authors.lastname: Li
mesh_terms: D000658:Amoxicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D000890:Anti-Infective Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001706:Biopsy; D002648:Child; D017291:Clarithromycin / Q000494:pharmacology; D004352:Drug Resistance, Microbial / Q000187:drug effects; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects*; D016481:Helicobacter Infections / Q000188:drug therapy / Q000382:microbiology; D016480:Helicobacter pylori / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D008795:Metronidazole / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests / Q000379:methods; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D008795:Metronidazole; D000658:Amoxicillin; D013752:Tetracycline; D017291:Clarithromycin