KG Hulten, et al. Gastroenterol 2021; 11: 1433-1442. Open Access: Comparison of Culture With Antibiogram to Next-Generation Sequencing Using Bacterial Isolates and Formalin-Fixed, Paraffin-Embedded Gastric Biopsies

Background: “The general unavailability of culture-based susceptibility testing for H pylori has resulted in the almost universal reliance on hopeful (empiric) therapy and a high proportion of treatment failures.” Besides the lack of availability of culture-based susceptibility testing, the global increase in prevalence of antimicrobial resistance contributes to the poor cure rates obtained with empiric use of the currently most popular triple therapies for H pylori infection.

Methods: H pylori isolates (n=170) (clinical isolates and formalin-fixed, paraffin-embedded) were tested for susceptibility to amoxicillin, clarithromycin, metronidazole, levofloxacin, tetracycline, and rifabutin using agar dilution and NGS targeted to 23S rRNA, gyrA, 16S rRNA, pbp1, rpoB and rdxA. Agreement was quantified using κ statistics.

Key findings:

• Agreement between agar dilution and NGS from culture isolates was very good for clarithromycin (κ = 0.90012), good for levofloxacin (κ = 0.78161) and fair for metronidazole (κ = 0.55880), and amoxicillin (κ = 0.21400)
• Comparison of NGS from tissue blocks and agar dilution from isolates from the same stomachs demonstrated good accuracy to predict resistance for clarithromycin (94.1%), amoxicillin (95.9%), metronidazole (77%), levofloxacin (87.7%), and tetracycline (98.2%)

Associated editorial: F Megraud et al. Gastroenterol 2021; 11: 1367-1369. Open Access: Molecular Diagnosis for Helicobacter pylori . . . at Last

Excerpts from editorial:

• “By targeting all of the genes responsible for antibiotic resistance, it is possible to obtain genotypic susceptibility data for all of the antibiotics of potential use, without the need to perform” culture and antibiotic susceptibility testing
• “Hulten et al show not only that they obtained comparable results with the reference method (phenotypic) for most of the antibiotics, but also that NGS can also be performed on both culture isolates and stored histologic preparations. This result is important because it avoids the need for extra biopsies and culture”
• “NGS could also be applied on stools. In this particular environment where H pylori DNA is found in a low amount, excellent DNA extraction methods are mandatory and progress is being made in this field”

My take: NGS can bring H pylori treatment to a new era (like almost all other infections). “Molecular methods can potentially augment or even replace the current in vitro methods for susceptibility testing, which are cumbersome, technically challenging, and time-consuming.”

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