Mechanisms of azithromycin resistance in Salmonella Typhi: molecular insights from dynamics behavior to clinical implications.

The widespread use of azithromycin during the COVID-19 pandemic has likely contributed to the increased resistance of Salmonella Typhi to this antibiotic. This study focuses on the extensive drug resistance (XDR) of Salmonella Typhi in Pakistan, analyzing 11,916 suspected typhoid fever cases, with 424 confirmed as Salmonella Typhi and Paratyphi A. Through antimicrobial susceptibility tests and PCR-based Sanger sequencing, an R717L mutation in the AcrB gene was identified, signalling the emergence of azithromycin resistance. This mutation was notably prevalent among XDR Salmonella Typhi isolates, with a high detection of blaCTX-M gp 1 (93%), followed by blaCTX-M 2 (87%) and blaTEM (81%). Detailed analysis revealed that the R717L mutation significantly alters the AcrB protein's interaction with azithromycin, evidenced by lower docking scores and reduced critical interactions, thus diminishing the antibiotic's affinity. Molecular Dynamics (MD) simulations further demonstrated that this mutation induces considerable structural changes in AcrB, impacting its stability and conformation. Additionally, binding free energy calculations showed decreased binding affinity of azithromycin to the mutated AcrB protein. These findings underscore the critical role of the R717L mutation in conferring drug resistance and highlight the urgent need for developing new antibiotic strategies to combat this growing threat. The evolution of azithromycin resistance in XDR Salmonella Typhi underscores the importance of cautious antibiotic use and the necessity for ongoing surveillance and research to inform effective typhoid fever treatment protocols.