Clarithromycin and amoxicillin susceptibility of Helicobacter pylori strains isolated from adult patients with gastric or duodenal ulcer in Italy.

Helicobacter pylori strains, isolated from 100 gastric biopsies from 49 previously untreated adult patients with endoscopy and histology-confirmed gastric or duodenal ulcer, were tested for in vitro antimicrobial susceptibility. Strains were isolated from biopsies of 75.5% (37 of 49) patients before therapy and of 13.5% after therapy. Clarithromycin and amoxicillin susceptibility testing was performed on pretreatment and posttreatment strains by using the agar disk diffusion method and E-test, a quantitative technique for the minimal inhibitory concentration (MIC) determination. All strains (n = 53) were susceptible to amoxicillin by the two methods. Three strains of 34 (8.8%) patients were resistant to clarithromycin: two by both methods and one by E-test (MIC > 2 microg/ml). E-test, although more expensive than the disk diffusion method, is easy to perform and is a reliable method for testing H. pylori susceptibility to antimicrobial agents in the clinical microbiology laboratory.