coli O157:H7 and P. aeruginosa by inhibiting polymeric matrix production [42]. Hence, indole and 3-indolylacetonitrile are possible spore maturation inhibitors against spore-forming P. alvei and biofilm inhibitors against pathogenic biofilm formation. Currently, various indole derivatives from plants and numerous synthetic indole derivatives are commercially available and work is in progress to identify universal and stronger sporocides and to understand their genetic mechanism in

action. Conclusions The current study demonstrates that i) indole is an extracellular stationary phase molecule in a Gram-positive bacteria P. alvei, ii) indole clearly inhibits spore maturation and Veliparib nmr survival rates under several stresses in P. alvei without affecting cell growth, iii) plant auxin 3-indolylacetonitrile dramatically decreased the heat resistance of P. alvei, iv) electron microscopy shows that indole and 3-indolylacetonitrile inhibit the development of spore coats and cortex in P. alvei. This study shows that indole, as a signaling molecule in quorum-sensing manner, plays a role in sporulation of P. alvei and that 3-indolylacetonitrile

can be useful to control of heat and antimicrobial resistant spores of Gram-positive bacteria. Methods Bacterial strains, materials and growth rate measurements P. alvei (ATCC 6344) and B. subtilis strain (ATCC6633) were obtained from Korean Culture Center of Microorganisms. FRAX597 cell line The strain was originally isolated from European foulbrood [43]. Luria-Bertani (LB) [44] was used as a basic medium for growth Anlotinib clinical trial unless indicated. DSM medium (Difco sporulation medium [45]) was used for spore formation and cell survival tests with antibiotics. DSM medium contains 8 g of Bacto nutrient broth (Difco), 10 ml of 10% KCl, 10 ml of 1.2% MgSO4·7H2O, 1.5 ml of 1 M NaOH, 1 ml of 1 M Ca(NO3)2, 1 ml of 0.01 M MnCl2 and 1 ml of 1 mM FeSO4 per liter. BHI agar medium (Difco brain heart infusion agar) was also used for long-term spore formation.

Indole, tryptophan, 3-indoleacetic acid, indole-3-carboxyaldehyde, 3-indolylacetonitrile, indole-3-acetamide, Ureohydrolase tryptamine, 2-oxindole, tetracycline, erythromycin, chloramphenicol, and streptomycin were purchased from Sigma-Aldrich Co. (Missouri, USA). Ethanol and dimethyl sulfoxide (DMSO) were purchased from Duksan Pure Chemical Co. (Ansan, Korea). Bacterial strains were initially streaked from -80°C glycerol stocks on LB plates, and a fresh single colony was inoculated into LB medium (25 ml) in 250 ml flasks and routinely cultured at 250 rpm at 37°C unless otherwise indicated. Overnight cultures were diluted in a 1:100 ratio using LB medium for cell growth and indole production or DSM medium for the test of spore surviving. For cell growth measurements, the optical density was measured at 600 nm (OD600) with a spectrophotometer (UV-160, Shimadzu, Japan). When the value of OD600 was above 0.