Journal: Cell

Article Title: Mining human microbiomes reveals an untapped source of peptide antibiotics

doi: 10.1016/j.cell.2024.07.027

Figure Lengend Snippet: (A) The synergistic interaction between pairs of SEPs from the same biogeography (tongue dorsum, supragingival plaque, and stool) was assessed by checkerboard assays with 2-fold serial dilutions starting at 2 × MIC to MIC/32. The histogram shows the fractional inhibitory indexes (FICIs) values obtained for each pair of SEPs, where dark red represents synergistic interactions, light red indicates additive interactions, and blue shows indifferent interactions. Most of the pairs of SEPs presented synergistic or additive interactions. To assess whether SEPs act on the bacterial membrane, all active SEPs against each of the pathogenic strains were tested in outer membrane permeabilization and cytoplasmic membrane depolarization assays. In general, SEPs presented low permeabilization of the outer membrane effect, as shown in (B) the relative fluorescence measurements of SEPs on A. baumannii cell membranes (see also ). SEPs showed high depolarization properties as shown in (C) the relative fluorescence measurements of SEPs on vancomycin-resistant E. faecium cytoplasmic membranes (see also ). The relative fluorescence was calculated with a non-linear fitting using as baseline the untreated control (buffer + bacteria + fluorescent dye) as described in the section. The correlation between cytotoxicity on (D) human colorectal adenocarcinoma cells (Caco-2) or (E) immortalized human keratinocytes (HaCaT) and antimicrobial activity is shown in a scatterplot where the cytotoxicity is represented by the CC 50 values (cytotoxic concentrations causing 50% cell death) and MIC (minimal inhibitory concentration for complete bacterial killing). CC 50 values have been predicted by interpolating the dose-response with a non-linear regression curve. The green area represents the therapeutic window where those peptides could be safely used with no toxic effect to eukaryotic cells (see also and ). See also and .

Article Snippet: To assess the potential antimicrobial activity of the candidate SEPs, we chemically synthesized 78 sequences ( ) and tested them against 11 clinically relevant pathogenic strains: Acinetobacter baumannii ATCC 19606, three E. coli strains (ATCC 11775, AIC221, AIC222) including a colistin-resistant strain, Klebsiella pneumoniae ATCC 13883, two Pseudomonas aeruginosa strains (PAO1 and PA14), two Staphylococcus aureus strains (ATCC 12600 and ATCC BAA-1556) including a methicillin-resistant strain, vancomycin-resistant Enterococcus faecalis (ATCC 700802), and vancomycin-resistant Enterococcus faecium (ATCC 700221), several of which are considered ESKAPEE pathogens ( E. faecium , S. aureus , K. pneumoniae , A. baumannii , P. aeruginosa , Enterobacter spp., and E. coli ), and thus the most threatening bacterial pathogens in our society according to the World Health Organization ( ).

Techniques: Membrane, Fluorescence, Control, Bacteria, Activity Assay, Concentration Assay