Silver salts of carboxylic acid terminated generation 1 poly (propyl ether imine) (PETIM) dendron and dendrimers as antimicrobial agents against S. aureus and MRSA

Abstract

Novel therapeutic strategies are essential to address the current global antimicrobial resistance crisis. Branched molecules with multiple peripheral functionalities, known as dendrimers, have gained interest as antimicrobials and have varying levels of toxicity. Silver displays activity against several micro-organisms only in its positively charged form. In this study, silver salts of generation 1 (G1) poly (propyl ether imine) (PETIM) dendron and dendrimers were synthesised and evaluated for their antimicrobial potential against sensitive and resistant bacteria. The purpose was to exploit the multiple peripheral functionalities of G1 PETIM dendron and dendrimers for the formation of silver salts containing multiple silver ions in a single molecule for enhanced antimicrobial activity at the lowest possible concentration. G1 PETIM dendron, dendrimers and their silver salts were synthesised and characterised by FT-IR, ¹H NMR and ¹³C NMR. PETIM silver salts were evaluated against Hep G2, SKBR-3 and HT-29 cell lines for their cytotoxicity using the MTT assay. The G1 PETIM dendron/dendrimers, silver nitrate and silver salts of the G1 dendron (compound 13), G1 dendrimer with an aromatic core (compound 14) and an oxygen core (compound 15) were evaluated for activity against S. aureus and methicillin-resistant S. aureus (MRSA) by the broth dilution method. PETIM silver salts were found to be non-cytotoxic even up to 100 μg ml⁻¹. Minimum inhibitory concentration values of compounds 13, 14 and 15 against S. aureus were 52.1, 41.7 and 20.8 μg ml⁻¹ while against MRSA they were 125.0, 26.0 and 62.5 μg ml⁻¹, respectively. The calculated fractional inhibitory concentration index further indicated that compound 14 specifically displayed additive effects against S. aureus and synergism against MRSA. The enhanced antimicrobial activities of the PETIM dendron/dendrimer-silver salts against both sensitive and resistant bacterial strains widen the pool of available pharmaceutical materials for optimizing treatment of bacterial infections.