Fig. 1.
Antibiotic susceptibility ranking fails to predict the outcome of antibiotic exposure in a bistable community. (A) The two species L. plantarum (orange) and C. ammoniagenes (green) exhibit mutually inhibitory interactions. (B) Coculturing C. ammoniagenes and L. plantarum under a serial dilution protocol including dispersal reveals two alternative stable states in which either species outcompetes the other. Green (orange) curves show the C. ammoniagenes (L. plantarum) abundance in coculture over five cycles of growth and 30-fold dilution with dispersal (105 fresh cells per [210 µL] culture per day for each species, n = 3). Cartoons illustrate the experimental protocol and observed community dynamics. (C) C. ammoniagenes is more susceptible to chloramphenicol than L. plantarum. Shown is 24-h growth of monocultures of each species (n = 3) in the presence of chloramphenicol at different concentrations (normalized by the average growth in the absence of antibiotic). IC50 is measured as the average minimum concentration that inhibits growth by at least 50% (SI Appendix, Fig. S3 shows that our results are qualitatively robust to measuring IC50 via growth rate reduction). (D) The stable state dominated by C. ammoniagenes is the most resilient to chloramphenicol exposure. The time series shows the response of the community (monitored through species abundances) to temporary exposure to chloramphenicol. Top (Bottom) panel shows the results for three replicate cocultures starting from the stable state dominated by C. ammoniagenes (L. plantarum). Color scheme is as in B; pink color highlights the 24-h cycle under antibiotic exposure. (E) C. ammoniagenes exhibits a higher growth rate than L. plantarum. Shown is the time series for the optical density of each species in monoculture (n = 24). (F) Susceptibility (IC50) of C. ammoniagenes and L. plantarum to eight different antibiotics (mean ± SEM, n = 3). Data are ordered by susceptibility ratio: (Top) L. plantarum shows the highest susceptibility relative to the susceptibility of C. ammoniagenes. (G) Resilience of each stable state of the community to antibiotic exposure. Color-coded squares show the stable state reached by the community before (initial state) and after (final state) exposure to the indicated antibiotic (n = 3). (Right) The subway plot indicates the states that are resilient to each antibiotic perturbation. The dashed rectangle highlights the five cases in which predictions based on species susceptibility do not agree with the observed resilience. Ca, C. ammoniagenes; Lp, L. plantarum. Ery, erythromycin; Chl, chloramphenicol; Gen, gentamicin; Amp, ampicillin; Kan, kanamycin; Car, carbenicillin; Tet, tetracycline; Cip, ciprofloxacin.