DEMONSTRATION OF UNEXPECTED ANTIBIOTIC-RESISTANCE OF GENOTYPICALLY IDENTICAL HELICOBACTER-PYLORI ISOLATES

With use of multiple- and single-colony expansion procedures, the resu lts of susceptibility testing of Helicobacter pylori isolates from pat ients with duodenal ulcer were assessed by Etest. The H. pylori genoty pe was assessed by repetitive extragenic palindrome-based polymerase c hain reaction (REP-PCR), There was a high degree of genotypic heteroge neity between different patients, but a single REP-PCR pattern was fou nd for 92% of patients. In contrast, a high degree of phenotypic heter ogeneity was shown among the isolated colonies. Antibiogram susceptibi lity patterns differed only with respect to metronidazole but not with respect to clarithromycin or amoxicillin. The 42% rate of resistance to metronidazole determined with use of the conventional multiple-stra ins expansion method was increased to 92% when the single-colony expan sion method was used. Similarly, dual clarithromycin/metronidazole res istance was increased from 8% to 42% with single-colony expansion. Des pite evidence of a single genotype in most patients, single-colony exp ansion shows that routine susceptibility testing may greatly underesti mate the frequency of metronidazole resistance.