Short report

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

V J Warburton-Timms and C A M McNulty

Public Health Laboratory, Gloucestershire Royal Hospital, Great Western Road, Gloucester GL1 3NN, UK

Correspondence to:
Dr McNulty jwhiting{at}phls.nhs.uk

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 µg/ml), clarithromycin (2 µg/ml), or amoxicillin (0.5 µg/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.

Key Words: Helicobacter pylori • metronidazole • clarithromycin • susceptibility testing

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