title: An increase in Helicobacter pylori strains resistant to metronidazole: a five-year study.
abstract: BACKGROUND
  Metronidazole is one of the most commonly used antimicrobial agents for the treatment of Helicobacter pylori infection. Resistance to metronidazole has been reported worldwide but with a wide range of prevalence. We started using the classical triple therapy (bismuth, tetracycline, and metronidazole) for H. pylori infection in 1991 but recently have experienced a decline in its efficacy in curing the infection. Thus our aim was to investigate in a single center the prevalence of metronidazole-resistant H. pylori over a period of 5 years.
  
  
  METHODS
  A total of 1,015 different H. pylori strains collected over a period of 5 years were tested for sensitivity against metronidazole, ampicillin, tetracycline, and imipenem. Antibiotic sensitivity was tested by the disk diffusion and agar dilution methods. To elucidate further the possible relationship between these metronidazole-resistant strains, genomic DNA digestion by the Hae III endonuclease and ribotyping were undertaken in a selected group of isolates.
  
  
  RESULTS
  In 1991, 29 of 132 (22.0%) tested strains of H. pylori were found to be resistant to metronidazole. Since our initiation at that time of a triple therapy of bismuth, metronidazole, and tetracycline, the prevalence of metronidazole-resistant strains rose rapidly to 73.2% in 1995. All H. pylori isolates were sensitive to ampicillin, tetracycline, and imipenem. A high degree of genomic heterogeneity was found among these isolates. Thus it is unlikely that the resistant strains of H. pylori were originated from a single clone.
  
  
  CONCLUSIONS
  This study shows a rapid increase in metronidazole-resistant H. pylori with the use of an anti-Helicobacter regimen that contains metronidazole. We anticipate that the efficacy of metronidazole-containing anti-Helicobacter regimens will decline with the rapid rise in resistant strains of H. pylori.
authors.affiliation: Department of Microbiology, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, Hong Kong.
authors.forename: T K
authors.initials: TK
authors.lastname: Ling
authors.forename: A F
authors.initials: AF
authors.lastname: Cheng
authors.forename: J J
authors.initials: JJ
authors.lastname: Sung
authors.forename: P Y
authors.initials: PY
authors.lastname: Yiu
authors.forename: S S
authors.initials: SS
authors.lastname: Chung
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000667:Ampicillin / Q000494:pharmacology; D000863:Antacids / Q000008:administration & dosage / Q000627:therapeutic use; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D001729:Bismuth / Q000008:administration & dosage / Q000627:therapeutic use; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D004352:Drug Resistance, Microbial; D018432:Drug Resistance, Multiple; D004359:Drug Therapy, Combination; D005260:Female; D005756:Gastritis / Q000188:drug therapy / Q000382:microbiology*; D016481:Helicobacter Infections / Q000188:drug therapy / Q000382:microbiology*; D016480:Helicobacter pylori / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D015378:Imipenem / Q000494:pharmacology; D008297:Male; D008795:Metronidazole / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D012189:Retrospective Studies; D013752:Tetracycline / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: D000863:Antacids; D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D008795:Metronidazole; D015378:Imipenem; D000667:Ampicillin; D013752:Tetracycline; D001729:Bismuth