ANTIMICROBIAL RESISTANCE TESTING OF HELICOBACTER-PYLORI - A COMPARISON OF ETEST AND DISK DIFFUSION METHODS

Routine antimicrobial resistance testing of Helicobacter pylori is mor e commonly performed since the correlation between metronidazole resis tance and failure to eradicate using this drug, has been made. While r esistance testing of H. pylori by Etest is simple to perform, it is ex pensive compared to disk diffusion methods. In this study the Etest wa s compared with a modified Kirby-Bauer disk diffusion (NCCLS) method f or routine resistance screening of H. pylori. Fifty one pre-treatment isolates were tested against amoxycillin, metronidazole, tetracycline and erythromycin by both Etest and disk diffusion using NCCLS guidelin e strength disks. Clarithromycin was tested by Etest only. Nitroimidaz ole and macrolide resistance were detected using the modified Kirby-Ba uer disk diffusion method which correlated with Etest minimum inhibito ry concentration (MIG). Resistance rates were 49% for metronidazole an d 8% for clarithromycin. Cross resistance occurs with macrolides again st H. pylori and allows testing of erythromycin to predict resistance to clarithromycin. The very low MICs obtained with H. pylori against a moxycillin and tetracycline require the use of Etest or lower strength disk methods to be used.