A SIMPLE METHOD FOR DETERMINING METROINDAZOLE RESISTANCE OF HELICOBACTER-PYLORI

The reliability of methods for determination of Helicobacter pylori re sistance to metronidazole has been found to depend upon the incubation time, Because the disk diffusion method is more vulnerable than other methods to prolonged incubation, this method has not been recommended for H. pylori, However, because media designed for rapid growth of H. pylori have been introduced, the time has come to look at the clinica l usefulness of this inexpensive and simple method again, The correlat ion of readings obtained with the E test (AB Biodisk, Solna, Sweden) a nd Rosco's (Taastrup, Denmark) disk diffusion method for in vitro metr onidazole resistance determination for H. pylori with a short incubati on time (24 to 31 h) was studied, Plates which could not be read after 24 to 31 h were reincubated for another night, Fifty-seven consecutiv e clinical strains were tested, Because the rate of regrowth of H. pyl ori depends upon the age of the colonies inoculated, the reproducibili ty of resistance test results for young colonies versus old colonies w as also studied, Resistance plates could be read after 24 to 31 h of i ncubation for 28 of 29 strains when the inoculum consisted of young co lonies (3 to 4 days old), For these 29 strains, a high correlation (r = -0.937) was found between results obtained with the E test and those obtained with the disk diffusion test, A poorer correlation was found for old colonies (greater than or equal to 5 days old) (r = -0.742), which required a prolonged incubation for 8 of 23 strains, In conclusi on, short incubation was successfully applied with young colonies, Res ults obtained with the simple and inexpensive disk diffusion method co rrelated well with those obtained with the E test.