title: Morphological and Bactericidal Effects of Different Antibiotics on Helicobacter pylori.
abstract: BACKGROUND
  Helicobacter pylori (H. pylori) is a spiral Gram negative bacteria that can transform to the coccoid form in adverse conditions.
  
  
  OBJECTIVE
  The aim of this study was to determine the in vitro morphological and bactericidal effects of metronidazole, amoxicillin and clarithromycin on H. pylori.
  
  
  METHODS
  The standard strain 26695 of H. pylori was cultured on Brucella agar (BA) and the minimum inhibitory concentrations (MICs) of three antibiotics were determined by E-test method. The bacteria were exposed to antibiotics at 1/2 MIC, MIC and 2X MIC concentrations in Brucella broth (BB). Induced coccoid forms were confirmed by Gram staining and light microscopy. The viability of cells as well as the susceptibility of viable coccoids to antibiotics were examined using the flow cytometry method.
  
  
  RESULTS
  All of the three antibiotics at sub-MIC induced coccoid forms. The highest rates of coccoids (> 90%) were induced at 0.008 μg/mL concentration (1/2 MIC) of amoxicillin, 72 hours postexposure. Metronidazole and clarithromycin with 1/2 MIC (0.5 and 0.125 µg/mL respectively) induced lower rates of coccoid forms (60% and 40% respectively). Potent bactericidal effects on coccoids were observed with Metronidazole at 2X MIC and clarithromycin at MIC (0.25 µg/mL) (80 - 90%). Amoxicillin with MIC and 2X MIC had no bactericidal effect on coccoid forms.
  
  
  CONCLUSIONS
  Despite the good in vitro bactericidal effect of amoxicillin on spiral forms of H. pylori, this antibiotic has little effect on induced coccoids that may develop after the inappropriate in vivo antibacterial treatment. Hence, for successful therapy, it is essential not only to eradicate the spiral forms, but to eliminate the viable coccoids.
authors.affiliation: Department of Microbiology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, IR Iran.
authors.forename: Jamshid
authors.initials: J
authors.lastname: Faghri
authors.affiliation: Department of Microbiology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, IR Iran.
authors.forename: Farkhondeh
authors.initials: F
authors.lastname: Poursina
authors.affiliation: Department of Microbiology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, IR Iran.
authors.forename: Sharareh
authors.initials: S
authors.lastname: Moghim
authors.affiliation: Department of Immunology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, IR Iran.
authors.forename: Hamid
authors.initials: H
authors.lastname: Zarkesh Esfahani
authors.affiliation: Department of Microbiology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, IR Iran.
authors.forename: Bahram
authors.initials: B
authors.lastname: Nasr Esfahani
authors.affiliation: Department of Microbiology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, IR Iran.
authors.forename: Hossein
authors.initials: H
authors.lastname: Fazeli
authors.affiliation: Department of Biology, Islamic Azad University, Tonekabon branch, Tonekabon, IR Iran.
authors.forename: Nasrin
authors.initials: N
authors.lastname: Mirzaei
authors.affiliation: Department of Immunology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, IR Iran.
authors.forename: Azam
authors.initials: A
authors.lastname: Jamshidian
authors.affiliation: Department of Microbiology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, IR Iran.
authors.forename: Hajieh
authors.initials: H
authors.lastname: Ghasemian Safaei
keywords: Antibiotics; Coccoid Bacteria; Helicobacter pylori; Susceptibility