Antibiotic susceptibility of attached and free-floating Helicobacter pylori

Helicobacter pylori are found attached to mucous cells of the human stomach or under the mucous layer. Models mimicking the in vivo situation may be m ore suitable for H, pylori MIC determinations than traditional agar dilutio n methods, Megraud et al. (Antimicrobial Agents and Chemotherapy 1991, 35, 869-72) developed a model for measuring the susceptibility of attached and free-floating H. pylori. We have modified this model so that free-floating and attached H. pylori are treated in a more similar manner, before and aft er incubation with antibiotic, and performed additional controls to ensure H. pylori and tissue culture cells are not detrimentally affected and maint ain their viability during the course of the experiment, We found only 10% of plate-grown H. pylori were competent for attachment to HEp-2 cells; howe ver, all progeny of attached bacteria remained adherent. Killing curves wer e performed using 0, 0.001, 0.01, 0.1 and 1 mg/L amoxycillin, and 0, 0.0025 , 0.0075 and 0.01 mg/L clarithromycin, H. pylori divided at concentrations C 0.01 mg/L amoxycillin and less than or equal to 0.0025 mg/L clarithromyci n. Contrary to the previous study, using our modified method we found that HEp-2 adherent and free-floating H. pylori are equally susceptible to amoxy cillin (strains 26695, CCUG18943, CCUG19104 and CCUG19110) and clarithromyc in (strain 26695). Therefore, we find no evidence that attachment of H, pyl ori to eukaryotic cells increases their resistance to antibiotics compared with non-attached bacteria. Nonetheless, these results confirm confidence i n traditional MIC studies when a comparison is made between susceptible and resistant strains.