2072. Multicenter Evaluation of the Etest vs. Agar Dilution for Susceptibility Testing of Helicobacter pylori

Abstract

Background Helicobacter pylori is associated with peptic ulcer disease and gastric malignancy. Antimicrobial susceptibility testing (AST) is often requested for patients who fail eradication therapy. The CLSI reference method, agar dilution (AD), is not performed in most laboratories and maintaining organism viability during transit to a reference laboratory is difficult. We assessed the performance of the Etest (bioMerieux) as a method for H. pylori AST in comparison to AD.MethodsFrozen stocks of 82 H. pylori isolates with AD results previously reported by Mayo Clinic were prepared from the same plate for distribution to participating laboratories. Etest was performed at ARUP Laboratories and Cleveland Clinic (CC). For Etest, isolates were incubated for 72 hours in a microaerobic atmosphere. Aged Mueller–Hinton agar with 5% sheep blood plates were inoculated with a three McFarland suspension prepared in brain heart infusion broth. Etest strips were applied and MICs read after 72 hours of microaerobic incubation. Results were interpreted by applying CLSI and EUCAST breakpoints. Categorical agreement (CA), very major, major and minor errors (VME, ME, and mE) were determined for Etest using AD as the reference method. Isolates with errors were repeat tested in duplicate by Etest to determine the final results summarized below.ResultsFor clarithromycin, 65% of isolates were resistant (R) by AD; Etest results at each laboratory showed 97.5% CA (1 mE and 1 ME). For tetracycline, only 2.5% of isolates were R by AD; a single VME occurred at both ARUP and CC (98.8% CA) with the same isolate. The AD dilutions tested for amoxicillin prevented interpretation with EUCAST breakpoints. With one exception, amoxicillin Etest results were susceptible (S, ≤0.125 mg/L) at both laboratories (98.8% of MICs ± one dilution). Applying levofloxacin EUCAST breakpoints (S, ≤1 mg/L) to interpret ciprofloxacin results, 57.8% of isolates were R by AD. ARUP CA was 97.5% (1 ME, 1 VME) and CC CA was 96.3% (1 ME, 2 VMEs).ConclusionClarithromycin, tetracycline, and ciprofloxacin Etest results for H. pylori showed acceptable CA (>95%) at both testing sites compared with the AD reference method. The comparative ease of performance and reproducibility of the Etest may help standardize it as an AST method for H. pylori.Disclosures S. S. Richter, bioMerieux: Grant Investigator, Research grant; BD Diagnostics: Grant Investigator, Research grant; Roche: Grant Investigator, Research grant; Hologic: Grant Investigator, Research grant; Diasorin: Grant Investigator, Research grant; Accelerate: Grant Investigator, Research grant; Biofire: Grant Investigator, Research grant.