title: Medium effects on minimum inhibitory concentrations of nylon-3 polymers against E. coli.
abstract: Minimum inhibitory concentrations (MICs) against E. coli were measured for three nylon-3 polymers using Luria-Bertani broth (LB), brain-heart infusion broth (BHI), and a chemically defined complete medium (EZRDM). The polymers differ in the ratio of hydrophobic to cationic subunits. The cationic homopolymer is inert against E. coli in BHI and LB, but becomes highly potent in EZRDM. A mixed hydrophobic/cationic polymer with a hydrophobic t-butylbenzoyl group at its N-terminus is effective in BHI, but becomes more effective in EZRDM. Supplementation of EZRDM with the tryptic digest of casein (often found in LB) recapitulates the LB and BHI behavior. Additional evidence suggests that polyanionic peptides present in LB and BHI may form electrostatic complexes with cationic polymers, decreasing activity by diminishing binding to the anionic lipopolysaccharide layer of E. coli. In contrast, two natural antimicrobial peptides show no medium effects. Thus, the use of a chemically defined medium helps to reveal factors that influence antimicrobial potency of cationic polymers and functional differences between these polymers and evolved antimicrobial peptides.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Heejun
authors.initials: H
authors.lastname: Choi
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Saswata
authors.initials: S
authors.lastname: Chakraborty
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Runhui
authors.initials: R
authors.lastname: Liu
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America; Molecular Biophysics Program, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Gellman
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America; Molecular Biophysics Program, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: James C
authors.initials: JC
authors.lastname: Weisshaar
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry; D004926:Escherichia coli / Q000187:drug effects*; D057927:Hydrophobic and Hydrophilic Interactions; D008826:Microbial Sensitivity Tests; D009757:Nylons / Q000737:chemistry / Q000494:pharmacology*; D011108:Polymers / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D009757:Nylons; D011108:Polymers