Chlorogenic acid (CGA) is a natural chemical ester composed of caffeic acid and (-)-quinic acid, and is further metabolized into active compounds in the living body. Here, we aimed to provide fundamental information on the antimicrobial action of CGA and related compounds against the Gram-negative bacterium Escherichia coli IFO 3301. Bacteriostatic effects were assessed by spectrophotometry, and bactericidal effects were determined by enumerating viable cells on MacConkey agar plates. CGA and related compounds exhibited specific antimicrobial activity and corresponding reduction in log survival ratio, in which ferulic, isoferulic, benzoic, and hydroxybenzoic acids exhibited obvious antimicrobial activity against E. coli. In a timekill assay, it was observed that bactericidal effects were associated with treatment time, temperature, and dose. A reduction in log survival ratio was observed at low pH as well as under thermal stress condition. Thus, we demonstrated that CGA and related compounds have not only bacteriostatic effects but also bactericidal effects. Keywords bactericidal effect • bacteriostatic effect • chlorogenic acid • polyphenol Materials and MethodsMaterials. Dimethyl sulfoxide, quinic acid, and ferulic acid were purchased from WAKO Pure Chemical Industries Ltd. (Japan). Luria broth (LB), and benzoic, hydroxybenzoic, caffeic, and hippuric acids were purchased from SIGMA-ALDRICH (Japan).