OBJECTIVETo investigate the prevalence of resistance of Helicobacter pylori (H. pylori) to metronidazole (MTZ) and the distribution change of minimal inhibitory concentrations (MICs) in H. pylori from local children, evaluate the applicability of E-test for MIC determination, and display the propensity of acquired-resistance to MTZ after induction of resistance in vitro.

METHODSOne group of 44 H. pylori isolates obtained from Oct. 2002 to Nov. 2003 and another 83 H. pylori isolates obtained from Dec. 2004 to Jul. 2005 from the local children who underwent gastroscopy in the Children's Hospital affiliated to Zhejiang University Medical School and were diagnosed as H. pylori-associated gastritis or peptic ulcer were studied. Susceptibility was tested by agar dilution method or E-test method. In 11 randomly selected metronidazole-sensitive isolates (MTZ(S)), resistance was induced in vitro with MTZ.

RESULTSThe resistance rate was 31.8% (14/44) in the 44-islates obtained from Oct. 2002 to Nov. 2003 and 51.8% (43/83) (chi(2) = 4.64, P < 0.05) in 83-isolates obtained from Dec. 2004 to Jul. 2005, respectively. The distribution of MICs were < 0.125 - 128 mg/L and 0.25- > 256 mg/L, in which, the MIC(50) was 0.5 mg/L and 16 mg/L, the MIC(90) was 128 mg/L, respectively. Comparing to agar dilution method which is recommended by National Committee for Clinical Laboratory Standards (NCCLS) for MIC, E-test was significantly associated with agar dilution method (chi(2) = 32.38, P < 0.001). The sensitivity, specificity, agreement rate of E-test were 73.08%, 100%, 87.27%, respectively, while there were factors of 2(2) to 2(6) difference in MICs between the results obtained by E-test and agar dilution. For all the 11 MTZ(S) isolates inducted resistance in vitro with MTZ, 16 MICs were achieved through 7 - 9 (7.2 +/- 0.6) passages of induction in vitro, and 100% acquired-resistance to MTZ through 8 - 10 generations; as a result, 10 of 11 MTZ(S) isolates achieved stable high-level resistance (256 mg/L for 2 and > 256 mg/L for 8) and 1 stable 64 mg/L resistance to MTZ.

CONCLUSIONSThe prevalence of resistance to MTZ seems to be increasing in H. pylori from local children. To avoid missed diagnosis of H. pylori resistant to MTZ (MTZ(R)), agar dilution method was needed when detecting susceptibility of H. pylori to MTZ. Resistance to MTZ of H. pylori from children is readily induced in vitro.