枯草杆菌，学名为枯草芽孢杆菌(Bacillus subtilis)，属于芽孢杆菌属(Bacillus)为革兰氏阳性菌，是一种好气性菌，普遍存在于土壤及植物体表，在人体亦可发现在肠道内共生的枯草杆菌。型态上的主要特征是菌体表面生有鞭毛，体内形成的内生孢子可抵抗恶劣的外在环境而存活。最近的研究显示，枯草杆菌其实并不全然是好气性的。枯草杆菌在食品和饲料添加剂上广范使用，近年来使用在种子保护及生物防治上，也经常被拿来应用。临床医学上是属于安全性的有益微生物。

Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants and humans. A member of the genus Bacillus, B. subtilis is rod-shaped, and can form a tough, protective endospore, allowing it to tolerate extreme environmental conditions. B. subtilis has historically been classified as an obligate aerobe, though evidence exists that it is a facultative aerobe. B. subtilis is considered the best studied Gram-positive bacterium and a model organism to study bacterial chromosome replication and cell differentiation. It is one of the bacterial champions in secreted enzyme production and used on an industrial scale by biotechnology companies.