Background: The purpose of this study was to understand the function of rfaF  gene in Helicobacter pylori  antibiotic resistance.
Methods: The gene homologous recombination method was used for knockout and complementation of H. pylori rfaF  gene. Various constructed strains were analysed for drug sensitivity to amoxicillin (AMO), tetracycline (TET), clarithromycin (CLA), metronidazole (MET), levofloxacin (LEV), and chloramphenicol (CHL) by agar plate dilution method. Drug sensitivity was further confirmed using a growth inhibition curve. Ethidium bromide (EB) accumulation experiments were performed to assess cell membrane permeability. PCR and sequence analysis were used to detect the rfaF  gene.
Results: The minimum inhibitory concentrations (MIC) of TET, CHL, AMO, and CLA in 11,637 rfaF  knockout strain (ΔrfaF  strain) were 4, 4, 2, and 2 times higher than those in 11,637 wild type (WT) strain, respectively. A multidrug-resistant (MDR) ΔrfaF  strain also displayed the same trend; however, the degrees of increase were relatively small. Growth inhibition experiments indicated that the growth of the 11,637 ΔrfaF  strain was higher with antibiotics at the MIC of the 11,637 WT strain than that of 11,637 rfaF -complemented strain (ΔrfaF/rfaF  strain), whereas the 11,637 WT strain did not exhibit any growth. The 11,637 ΔrfaF  strain was significantly reduced compared with the cumulative EB fluorescence intensity of the 11,637 WT and of 11,637ΔrfaF/rfaF  strain, and the same trend appeared in the MDR strain. Among the 10 clinical strains, 9 clinical strains were found to have mutations in the conserved sequence of rfaF  amino acids.
Conclusion: We found a new drug resistance gene, rfaF , in H. pylori , which changes the permeability of cell membrane to confer cross-resistance to AMO, TET, CLA, and CHL and is involved in clinical strain drug resistance. It can be used as a drug target.
Keywords: rfaF , amoxicillin, clarithromycin, tetracycline, resistance