SLAP-S25 is a potent broad-spectrum

SLAP-S25 is a potent broad-spectrum antibiotic adjuvant. To screen potential adjuvants for antibiotics, we used an MDR iso-late Escherichia coli B2 carrying 25 antibiotic-resistant genes (ARGs) located on four plasmids and chromosomes to all major classes of antibiotics (see Supplementary Tables 1 and 2), to obtain candidates from our library of short linear antibacterial peptides (SLAPs) and their derivatives through accessible chemical synthesis23–25. SLAPs are the derivatives of non-ribosomal peptides that are synthesized through giant non-ribosomal peptide synthetases26. Given that previous studies exhibit the synergistic activity between peptides and antibiotics15,16, we subsequently performed a chequerboard assay to determine the potency of SLAPs in combination with existing antibiotics.We found a candidate-designated SLAP-S25, which showed the ability to restore the efficiency of different classes of antibiotics against E. coli B2. SLAP-S25 is a synthetic undecapeptide with acet-ylation at the N terminus and amidation at the C terminus (Fig. 1a). SLAP-S25 solely exhibited weak antibacterial activities against either Gram-positive or Gram-negative bacteria (see Supplementary Table 3), with a minimum inhibitory concentration (MIC) of 12 μg ml−1 for E. coli B2. Notably, we observed broad synergies between SLAP-S25 at sub-MIC levels (≤4 μg ml−1) and other major classes of antibiotics against E. coli B2 (Fig. 1b,c, and see Table 1 and Extended Data Fig. 1), including tetracycline, ofloxacin, rifampicin, cefepime and vanco-mycin. For example, the MIC of colistin decreased 32-fold from 8 μg ml−1 to 0.25 μg ml−1 in the presence of 4 μg ml−1 of SLAP-S25 (see Extended Data Fig. 1). In addition, SLAP-S25 showed synergies with multiple antibiotics against diverse, antibiotic-sensitive, E. coli isolates (see Supplementary Table 4)