A Trojan-Horse Strategy Including a Bacterial Suicide Action for the Efficient Use of a Specific Gram-Positive Antibiotic on Gram-Negative Bacteria

In the alarming context of rising bacterial antibiotic resistance, there is an urgent need to discover new antibiotics or increase and/or enlarge the activity of those currently in use. The need for new antibiotics is even more urgent in the case of Gram-negative bacteria, such as Acinetobacter, Pseudomonas, and Enterobacteria, which have become resistant to many antibiotics and have an outer membrane with very low permeability to drugs. Vectorization of antibiotics using siderophores may be a solution to bypass such a bacterial wall: the drugs use the iron transporters of the outer membrane as gates to enter bacteria in a Trojan-horse strategy. Designing siderophore-antibiotics that can cross outer membranes has become almost routine, but their transport across the inner membrane is still a limiting step, as well as a strategy that allows dissociation of the antibiotic from the siderophore once inside the bacteria. Liu et al. (J. Med. Chem. 2018, DOI:10.1021/acs.jmedchem.8b00218) report the synthesis of a siderophore-cephalosporin compound and demonstrate that beta-lactams, such as cephalosporins, can serve as beta-lactamasetriggered releasable linkers to allow intracellular delivery of Gram-positive antibiotics to Gram-negative bacteria.