Membrane-Activating Triphenylphosphonium Functionalized Ciprofloxacin for Multidrug Resistant Bacteria

Multidrug resistant (MDR) bacteria have become a severe problem for public health. Developing new antibiotics for MDR bacteria is difficult, from inception to the clinically approved stage. Here, we have used a new approach; we have modified the antibiotic, ciprofloxacin (CFX), with triphenylphosphonium (TPP, PPh3) moiety via ester- (CFX-ester-PPh3) and amide-coupling (CFX-ester-PPh3), to target bacterial membranes. In this study, we have evaluated the antibacterial activities of CFX and its derivatives against 16 species of bacteria, including MDR bacteria, using minimum inhibitory concentration (MIC) assay, morphological monitoring, and expression of resistance-related genes. TPP-conjugated CFX, CFX-ester-PPh3 and CFX-amide-PPh3 showed significantly improved antibacterial activity against Gram-positive bacteria, Staphylococcus aureus, including MDR S. aureus (MRSA) strains. The MRSA ST5 5016 strain showed high antibacterial activity, with an MIC values of 11.12 µg/mL for CFX-ester-PPh3 and 2.78 µg/mL for CFX-amide-PPh3. The CFX derivatives inhibited biofilm formation in MRSA by more than 74.9% of CFX-amide-PPh3. In the sub-MIC, CFX derivates induced significant morphological changes in MRSA, including irregular deformation and membrane disruption, accompanied by a decrease in the level of resistance-related gene expression. With these promising results, this method is very likely to combat MDR bacteria, through a simple TPP moiety modification of known antibiotics, which can be readily prepared at clinical sites.