Role of screening agar plates for in vitro susceptibility testing of Helicobacter pylori in a routine laboratory setting

Background-Resistance of Helicobacter pylori to the more frequently used antibiotics (metronidazole and clarithromycin) reduces eradication rates even with triple treatment. Determining the antibiogram profile of H pylori can take up to 14 days and delays appropriate treatment. Aims-To determine the role of screening agar plates for more rapid in vitro susceptibility of H pylori to metronidazole, amoxicillin, and clarithromycin. Methods-Routine gastric biopsy specimens from 507 dyspeptic patients were inoculated on to 10% lysed blood agar plates containing metronidazole (8 mug/ mi), clarithromycin (2 mug/ml), or amoxicillin (0.5 mug/ml). The minimum inhibitory concentration (MIC) of the 90 isolates was determined using the E test. Results-Metronidazole resistance was detected in 28 of 90 isolates by E test and nine of 98 by screening agar. The screening agar detected none of the four clarithromycin resistant isolates detected by the E test. Conclusions-The screening agar method is not sufficiently sensitive to be used alone.