Susceptibilities to clarithromycin, amoxycillin and metronidazole of Helicobacter pylori isolates from the antrum and corpus in Tokyo, Japan, 1995-2001.

The aim of this study was to determine the susceptibilities to clarithromycin, amoxycillin and metronidazole of Helicobacter pylori isolates from the antrum and corpus of Japanese patients examined during the period 1995-2001. There was an increase, from 6.2% in 1995 to 22.1% in 2000-2001, in the proportion of patients infected with clarithromycin-resistant H. pylori. Of patients infected with clarithromycin-resistant H. pylori, 39.1% were infected with both clarithromycin-susceptible and -resistant H. pylori. Furthermore, the MIC90 of clarithromycin for H. pylori rose from < 1 mg/L in 1995-1998 to 8 mg/L in 1999. In contrast, the MIC90s of amoxycillin and metronidazole were < or = 0.125 and 4 mg/L, respectively, throughout the study period. The results showed that, while most H. pylori isolates were susceptible to amoxycillin and metronidazole, resistance to clarithromycin among H. pylori isolates increased markedly in Japan during 1995-2001. The results also indicated a need to test the susceptibility of H. pylori isolates from more than two samples obtained from two different sites in the stomach of a single patient in order to diagnose the presence of clarithromycin-resistant H. pylori correctly.