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The current need for novel antibiotics is especially acute for drug-resistant Gram-negative pathogens1,2. These microorganisms have a highly restrictive permeability barrier, which limits the penetration of most compounds3,4. As a result, the last class of antibiotics that acted against Gram-negative bacteria was developed in the 1960s2. We reason that useful compounds can be found in bacteria that share similar requirements for antibiotics with humans, and focus on Photorhabdus symbionts of entomopathogenic nematode microbiomes. Here we report a new antibiotic that we name darobactin, which was obtained using a screen of Photorhabdus isolates. Darobactin is coded by a silent operon with little production under laboratory conditions, and is ribosomally synthesized. Darobactin has an unusual structure with two fused rings that form post-translationally. The compound is active against important Gram-negative pathogens both in vitro and in animal models of infection. Mutants that are resistant to darobactin map to BamA, an essential chaperone and translocator that folds outer membrane proteins. Our study suggests that bacterial symbionts of animals contain antibiotics that are particularly suitable for development into therapeutics.

Multidrug tolerance is largely responsible for chronic infections and caused by a small population of dormant cells called persisters. Selection for survival in the presence of antibiotics produced the first genetic link to multidrug tolerance: a mutant in the Escherichia coli hipA locus. HipA encodes a serine-protein kinase, the multidrug tolerance activity of which is neutralized by binding to the transcriptional regulator HipB and hipBA promoter. The physiological role of HipA in multidrug tolerance, however, has been unclear. Here we show that wild-type HipA contributes to persister formation and that high-persister hipA mutants cause multidrug tolerance in urinary tract infections. Perplexingly, high-persister mutations map to the N-subdomain-1 of HipA far from its active site. Structures of higher-order HipA–HipB–promoter complexes reveal HipA forms dimers in these assemblies via N-subdomain-1 interactions that occlude their active sites. High-persistence mutations, therefore, diminish HipA–HipA dimerization, thereby unleashing HipA to effect multidrug tolerance. Thus, our studies reveal the mechanistic basis of heritable, clinically relevant antibiotic tolerance. The molecular basis of multidrug tolerance in chronic urinary tract infections is mediated by mutations in the N-subdomain-1 of the Escherichia coli HipA protein kinase. The spread of multidrug tolerance among bacterial pathogens is mainly due to the existence of 'persisters', phenotypic variants that lie dormant and so are not susceptible to antibiotics that are effective only against actively growing cells. Maria Schumacher et al. show here that wild-type HipA, a serine protein kinase that inhibits protein synthesis and drives cells into dormancy, contributes to persister formation in Escherichia coli, and that hipA7 high-persister mutants are present in patients with urinary tract infections. The authors determine the structures of transcription autorepression complexes consisting of promoter DNA and HipA–HipB complexes. These structures reveal that high-persistence mutations function by interfering with HipA–HipA interactions, releasing HipA from the higher-order complex and triggering multidrug tolerance.

Chronic infections are difficult to treat with antibiotics but are caused primarily by drug-sensitive pathogens. Dormant persister cells that are tolerant to killing by antibiotics are responsible for this apparent paradox. Persisters are phenotypic variants of normal cells and pathways leading to dormancy are redundant, making it challenging to develop anti-persister compounds. Biofilms shield persisters from the immune system, suggesting that an antibiotic for treating a chronic infection should be able to eradicate the infection on its own. We reasoned that a compound capable of corrupting a target in dormant cells will kill persisters. The acyldepsipeptide antibiotic (ADEP4) has been shown to activate the ClpP protease, resulting in death of growing cells. Here we show that ADEP4-activated ClpP becomes a fairly nonspecific protease and kills persisters by degrading over 400 proteins, forcing cells to self-digest. Null mutants of clpP arise with high probability, but combining ADEP4 with rifampicin produced complete eradication of Staphylococcus aureus biofilms in vitro and in a mouse model of a chronic infection. Our findings indicate a general principle for killing dormant cells-activation and corruption of a target, rather than conventional inhibition. Eradication of a biofilm in an animal model by activating a protease suggests a realistic path towards developing therapies to treat chronic infections.

Nature 517, 455–459 (2015); doi:10.1038/nature14098 In Fig. 3d of this Article, the ‘2:1’ and ‘1:1’ labels at the bottom of the panel were inadvertently switched during the production process; this figure has now been corrected in the online versions of the paper.

Bacterial evolution is overwhelming our antibiotic defences, says Kim Lewis. Using modern technology to replicate past success might tip the balance in our favour.