Antimicrobial susceptibility testing for Helicobacter pylori: Sensitivity test results and their clinical relevance

There are multiple test methodologies to determine the antibiogram of an or ganism. Standardized susceptibility test methods are based upon rapidly gro wing, aerobic microorganisms in which overnight incubation results in defin itive endpoints. In vitro susceptibility testing for fastidious organisms t hat require complex media for growth, require incubation in atmospheres oth er than ambient air, or are slow-growing (anaerobes, mycobacteria, filament ous fungi) are problematic and in general are not standardized. H. pylori f alls into this category of troublesome organisms. For the microaerobic orga nism H. pylori, testing is challenging because the organism grows slowly ev en under optimal culture conditions. Recently the National Committee for Cl inical Laboratory Standards (NCCLS) approved the agar dilution method as th e test of choice for testing H. pylori. While not entirely reliable in pred icting the outcome of treatment for metronidazole resistant organisms, the resistance determined for clarithromycin by this method generally predicts treatment failure. Quality control breakpoints for H. pylori ATCC 43504 wer e established and breakpoints for clarithromycin were approved by the NCCLS in 1999. Breakpoints are minimum inhibitory concentrations (MIC) of a drug at which an organism is deemed either susceptible or resistant to the anti biotic using standard dosing regimens containing that drug. Significant pro gress has been made with respect to development of tests to detect antimicr obial resistance, but there still. remains no consensus as to the breakpoin ts for agents used in the treatment of H. pylori infection other than clari thromycin. This article will address the controversies associated with the reporting of antibiotic resistance data and the interpretation of these dat a.