A novel bactericidal small molecule, STK-35, and its derivative, STK-66, as antibacterial agents against Gram-negative pathogenic bacteria in vitro and in vivo.

Due to the increasing rate of antibiotic resistance and the emergence of persister cells of Gram-negative pathogenic bacteria, the development of new antibacterial agents is urgently needed to deal with this problem. Our results indicated that both newly identified small molecule STK-35 and its derivative STK-66 exhibited effective antibacterial properties against a variety of Gram-negative pathogens including Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. The minimal inhibitory concentrations and minimal bactericidal concentrations ranges were 0·0625-8 μg ml-1 and 0·125-16 μg ml-1 , respectively, while no haemolytic activity and mammalian cell cytotoxicity were observed. The time-killing assays showed STK-35/66 had strong bactericidal activity against Gram-negative pathogens. STK-35/66 also showed different degrees of synergistic antibacterial activity with conventional antibiotics and exhibited persister cells killing activity. Moreover, STK-35/66 effectively eradicated the pre-formed biofilms of P. aeruginosa and A. baumannii. In addition, STK-35/66 significantly increased the survival rate of E. coli infected mice and induced a decrease in bacterial load of the peritonitis model. In nutshell, these results suggested that STK-35/66 possessed antimicrobial activity against Gram-negative pathogenic bacteria in vitro and in vivo, which could be considered as potential substitutes for the treatment of Gram-negative pathogenic infections after further structure optimization.