Delafloxacin and levofloxacin activities on Helicobacter pylori in Bulgaria over four years.

Delafloxacin is a potent 4th-generation fluoroquinolone with enhanced activity in acidic environments. However, recently, delafloxacin resistance in facultative anaerobic species has been reported. Thus, we examined levofloxacin and delafloxacin susceptibility of 98 Helicobacter pylori strains in 2020-2023. Minimum inhibitory concentrations (MICs) were detected with E tests. Levofloxacin resistance was 33.7%, while delafloxacin resistance was 2.0% at 1 mg/l (the levofloxacin resistance breakpoint for H. pylori), and 9.2% at 0.125 mg/l (the recently suggested delafloxacin ECOFF for the species). Overall proportion of the strains exhibiting >0.125 mg/l delafloxacin MICs was similar to that in the previous study in 2018-2019 (8.5%). None of the 65 levofloxacin susceptible strains had delafloxacin MICs of >0.125 mg/l. Among levofloxacin resistant strains, delafloxacin MICs >1 mg/l (6.1%, 2/33 strains) were detected only in 2022 and 2023. Briefly, the results showed the much higher activity of delafloxacin over levofloxacin. The high delafloxacin activity in acidic environments is an additional advantage of the newer fluoroquinolone for treating H. pylori infection. Given that fluoroquinolone-based eradication regimens can be used as a second- or third-line therapy for H. pylori, testing the susceptibility of levofloxacin-resistant strains to delafloxacin could provide a useful option for eradication of the frequent and potentially carcinogenic bacteria. New regimens, such as the combination of vonoprazan with delafloxacin and another antibiotic deserve investigation.