Multilaboratory Comparison of Proficiencies in Susceptibility Testing of Helicobacter pylori and Correlation between Agar Dilution and E Test Methods

Abstract

Susceptibility testing was performed at seven Canadian microbiology laboratories and the Helicobacter Reference Laboratory, Halifax, Nova Scotia, Canada, to assess susceptibility testing proficiency and the reproducibility of the results for clarithromycin and metronidazole and to compare the Epsilometer test (E test) method to the agar dilution reference method. Control strain Helicobacter pylori ATCC 43504 (American Type Culture Collection) and 13 clinical isolates (plus duplicates of four of these strains including ATCC 43504) were tested blindly. The National Committee for Clinical Laboratory Standards (NCCLS) guidelines for agar dilution testing were followed, and the same suspension of organisms was used for agar dilution and E test. Antimicrobials and E test strips were provided to the investigators. Methods were provided on a website (www.Helicobactercanada.org). Each center reported MICs within the stated range for strain ATCC 43504. Compared to the average MICs, interlaboratory agreements within 2 log 2 dilutions were 90% (range, 69 to 100%) for clarithromycin by agar dilution, with seven very major errors [VMEs], and 85% (range, 65 to 100%) by E test, with three VMEs. Interlaboratory agreements within 2 log 2 dilutions were 83% (range, 50 to 100%) for metronidazole by agar dilution, with six VMEs and eight major errors (MEs), and 75% (range, 50 to 94%) by E test, with four VMEs and four MEs. At lower and higher concentrations of antibiotic, E test MICs were slightly different from agar dilution MICs, but these differences did not result in errors. When a standardized protocol based on NCCLS guidelines was used, most participants in this study correctly identified clarithromycin-and metronidazole-susceptible and -resistant strains of H. pylori 93% of the time by either the agar dilution or E test method, and the numbers of errors were relatively equivalent by both methods.

Antimicrobial Susceptibility and Mutations Involved in Clarithromycin Resistance in Helicobacter pylori Isolates from Patients in the Western Central Region of Colombia

“…Both the Etest and PCR-RFLP detected the same four clarithromycin-resistant isolates, as has previously been reported (3,10). Results obtained by PCR-RFLP help to specify the mechanism of H. pylori clarithromycin resistance, and this technique could also be applied directly to stool or biopsy samples (18,22).…”

“…The usual phenotypic methods for susceptibility testing can be applied to H. pylori (3,10). Numerous genotypic methods have been developed to detect clarithromycin resistance (16); the common methods used are PCR-restriction fragment length polymorphism (RFLP) and real-time PCR (17).…”

Prevalence of Resistance of Helicobacter pylori Strains to Selected Antibiotics in Isfahan, Iran

“…These breakpoints were used based on the recommendations of the National Committee for Clinical Laboratory Standards (NCCLS) (11,(18)(19)(20)(21)(22).…”

Validation of a Fluorescence In Situ Hybridization Method Using Peptide Nucleic Acid Probes for Detection of Helicobacter pylori Clarithromycin Resistance in Gastric Biopsy Specimens

“…The agar dilution method is the reference method proposed by the Clinical and Laboratory Standards Institute (CLSI), formerly the National Committee for Clinical Laboratory Standards, to be used for H. pylori antibiotic susceptibility testing (19,20). Alternatively, clinical laboratories use the Etest method as it is considered less technically demanding (21,22).…”