Etest to detect drug-resistant Neisseria gonorrhoeae to contemporary treatment; methodological issues concerning accuracy and reproducibility

I was interested to read the paper by Papp and colleagues published in the Journal of Medical Microbiology 2018. Neisseria gonorrhoeae is a sexually transmitted bacterial pathogen that continues to evolve to become resistant to known antibiotics. The authors aimed to examine the intra-laboratory variability of using the Etest method to provide consistent MIC values for N. gonorrhoeae and also compared the results of the Etest to known agar dilution MIC values [1]. Clinical N. gonorrhoeae isolates, 100 paired duplicates, were tested by 8 laboratories for antibiotic susceptibility to ceftriaxone, cefixime and azithromycin using Etest strips. The authors reported that, overall, >80% of the paired Etest MIC values were within one log2 dilution of the replicate. When compared to the agar dilution reference method, the cefixime Etest MIC values were consistently underreported by one dilution (seven laboratories) or two dilutions (one laboratory). The azithromycin Etest MIC values agreed 90.7% with the agar dilution MIC values, while the agreement with ceftriaxone was 90.9%.