Bactericidal and morphological effects of amoxicillin on Helicobacter pylori.

The growth kinetics of Helicobacter pylori after it has been exposed to amoxicillin have been investigated in conjunction with studies of cell morphology. A potent bactericidal effect was observed at concentrations 10-fold higher than the MIC, but this was accompanied by an increase in the residual numbers of coccoid forms observed. In the presence of 10 micrograms of amoxicillin per ml, these forms could be detected as rapidly as 6 h after exposure to the antibiotic. Although the clinical relevance of coccoid forms remains unknown, such forms should be considered when potential anti-Helicobacter agents are tested in vitro.