Morphological and bactericidal effects of amoxicillin and clarithromycin on Helicobacter pylori

Abstract number: o302

Can  F., Demirbilek  M., Karabay  G., Arslan  H.

Background: 

Coccoid forms of Helicobacter pylori are suspected to play an important role on transmission and relapsing of infection. Amoxicillin and clarithromycin are used for H. pylori eradication therapy. This study focused on the growth kinetics of H. pylori after being exposed to amoxicillin, clarithromycin and different amoxicillin-clarithromycin combinations with the conjunction of cell morphology.

Methods: 

H. pylori NCTC 11637 inoculated into Brucella Broth with 2.5% fetal calf serum was exposed to -10xMIC, -1xMIC, 1xMIC, 10xMIC concentrations of antibiotics either alone or in combination. Growth characteristics were determined by the time kill assay. TEM was used for ultra structural morphology.

Results: 

Amoxicillin and clarithromycin alone decreased the viable counts of H. pylori, depending on the antibiotic concentrations. Exposure to these antimicrobials resulted in morphological changes of cell shape, cell-wall disintegration and cell lyses. Amoxycillin showed the most potent effect on viability and morphology of H. pylori, which was accompanied with the increase of coccoid forms at a concentration 10 fold higher than the MIC, as rapidly as 6 hours inoculation. The effects of clarithromycin were observed after 12 hours of inoculation. Amoxicillin plus clarithromycin combinations showed additive effect on viable counts and caused a decrease in morphological changes.

Conclusion: 

Our results showed that amoxicillin-clarithromycin combination caused a decreased frequency in transformation to coccoid forms and higher growth inhibition than amoxicillin exposure alone. Although the clinical importance of coccoid forms is unknown; these forms should be take in to consideration when anti-Helicobacter pylori agents are tested in vitro.