Molecular Characterization and Mutational Analysis of Clarithromycin- and Levofloxacin-Resistance Genes in from Gastric Biopsies in Southern Croatia.

Point mutations in the , , and genes can confer resistance to clarithromycin (CAM) and levofloxacin (LVX) by altering target sites or protein structure, thereby reducing the efficacy of standard antibiotics in the treatment of infections. Considering the confirmed primary CAM and LVX resistance in infected patients from southern Croatia, we performed a molecular genetic analysis of three target genes (, and ) by PCR and sequencing, together with computational molecular docking analysis. In the CAM-resistant isolates, the mutation sites in the gene were A2142C, A2142G, and A2143G. In addition, the mutations D91G and D91N in GyrA and N481E and R484K in GyrB were associated with resistance to LVX. Molecular docking analyses revealed that mutant strains with resistance-related mutations exhibited a lower susceptibility to CAM and LVX compared with wild-type strains due to significant differences in non-covalent interactions (e.g., hydrogen bonds, ionic interactions) leading to destabilized antibiotic-protein binding, ultimately resulting in antibiotic resistance. Dual resistance to CAM and LVX was found, indicating the successful evolution of resistance to unrelated antimicrobials and thus an increased risk to human health.