Acetamido derivatives of the naturally antibacterial non-β-lactam lactivicin (LTV) have improved activity against their penicillin binding protein targets and reduced hydrolysis by β-lactamases, but penetration into Gram-negative bacteria is still relatively poor. Here we report that modification of the LTV lactone with a catechol-type siderophore increases potency 1,000-fold against Stenotrophomonas maltophilia, a species renowned for its insusceptibility to antimicrobials. The MIC90 of modified lactone compound 17 (LTV17) against a global collection of extensively drug-resistant clinical S. maltophilia isolates was 0.063 μg · ml(-1) Sideromimic modification does not reduce the ability of LTVs to induce production of the L1 and L2 β-lactamases in S. maltophilia and does not reduce the rate at which LTVs are hydrolyzed by L1 or L2. We conclude, therefore, that lactivicin modification with a siderophore known to be preferentially used by S. maltophilia substantially increases penetration via siderophore uptake. LTV17 has the potential to be developed as a novel antimicrobial for treatment of infections by S. maltophilia More generally, our work shows that sideromimic modification in a species-targeted manner might prove useful for the development of narrow-spectrum antimicrobials that have reduced collateral effects.