2.5. Antibiotic Susceptibility Test

Antibiotic susceptibility of isolated H. pylori strains was performed by the E-test (BioMérieux) determining the minimum inhibitory concentrations (MICs) against amoxicillin, clarithromycin, levofloxacin, metronidazole, rifampicin, and tetracycline. A bacterial suspension was prepared in BB supplemented with 10% HS and 200 μL of this suspension was transferred onto the surface of the MHB and streaked with a cotton swab. Antibiotic strips were applied onto the surface of inoculated and dried agar plates. The plates were incubated in a microaerophilic incubator (VAIN) at 37 °C for 72 h before examination. MIC was determined by considering the point where ellipse growth cut with the scale number in the E-test strip. The breakpoints were defined as follows: amoxicillin, MIC > 0.125 μg/mL; clarithromycin, MIC > 0.5 μg/mL; levofloxacin, MIC > 1 μg/mL; metronidazole, MIC > 8 μg/mL; rifampicin, MIC > 1 μg/mL; and tetracycline, MIC > 1 μg/mL, following the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines (version 8.0). Strain Hp11637 (NCTC) was used as experimental control.