Antimicrobial combinations against Helicobacter pylori including benzoxadiazol-based flavodoxin inhibitors: in vitro characterization

Antimicrobial resistance of Helicobacter pylori (Hp) threatens currently available treatment regimens and prompts the development of antimicrobial drugs against new bacterial targets. One such class of drugs is Hp-flavodoxin (Hp-fld) inhibitors, which target an essential metabolic pathway in Hp. The aim of this study was to characterize the effects of these inhibitors against Hp over time when used alone or combined with conventional antibiotics. Four benzoxadiazol-based fld inhibitors were initially tested for their in vitro potency, with compound IV displaying the highest efficacy. This compound was then combined with clarithromycin, metronidazole, amoxicillin, levofloxacin, and rifampicin in further experiments. Checkerboard assays indicated that compound IV exhibited additive activity when combined with these antibiotics. The study further investigated the time course of antibacterial effects by exposing a high inoculum of Hp to compound IV and each antibiotic, alone or in combination. At just four times the minimum inhibitory concentration, compound IV demonstrated bactericidal effects within 6 h. However, the regrowth of bacteria occurred between 24 and 48 h of exposure. Similar patterns of killing followed by regrowth were observed for conventional antibiotics alone. However, the addition of compound IV to the antibiotics clearly limited regrowth over 72 h. These findings suggest that compound IV can effectively eliminate spontaneous mutants that are resistant to conventional antibiotics or prevent new mutations during drug exposure. Hp-fld inhibitors, such as compound IV, hold promise as new drugs to be integrated into Hp infection treatment, potentially reducing the development of resistance and shortening the duration of treatment. IMPORTANCE The antimicrobial resistance of Helicobacter pylori (Hp) currently poses a threat to available treatment regimens. Developing antimicrobial drugs targeting new bacterial targets is crucial, and one such class of drugs includes Hp-flavodoxin (Hp-fld) inhibitors that target an essential metabolic pathway in Hp. Our study demonstrated that combining these new drugs with conventional antibiotics used for Hp infection treatment prevented the regrowth observed with drugs used alone. Hp-fld inhibitors show promise as new drugs to be incorporated into the treatment of Hp infection, potentially reducing the development of resistance and shortening the treatment duration.