Antimicrobial Activity of Luteolin against Trueperella pyogenes

The T. pyogenes strain ATCC19411 was obtained from the American Type Culture Collection (Manassas, VA, USA). The T. pyogenes strains (BM07-1, BMH06-3, and T001-T017) were isolated from dairy cattle and preserved in our laboratory. The resistance phenotypes of T. pyogenes and the minimum inhibitory concentrations (MICs) of luteolin against T. pyogenes are shown in Table S1 [24 (link),32 (link)]. T. pyogenes strains were maintained on Mueller-Hinton Agar (MHA, Solarbio, Beijing, China) supplemented with 5% (v/v) sheep blood (Hopebio, Qingdao, China) under microaerophilic conditions (5% CO₂) at 37 °C for 36 h. The resulting colonies were inoculated in nutrient broth (NB, Solarbio) supplemented with 8% (v/v) fetal bovine serum (FBS, Gibco, Grand Island, NE, USA). Luteolin was obtained from Pureone Biotechnology Co., Ltd. (Shanghai, China) and dissolved in 1% dimethyl sulfoxide (DMSO, Sigma-Aldrich, Shanghai, China) to prepare a stock solution.