Bacillus is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum Bacillota, with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural Bacilli is the name of the class of bacteria to which this genus belongs. Bacillus species can be either obligate aerobes which are dependent on oxygen, or facultative anaerobes which can survive in the absence of oxygen. Cultured Bacillus species test positive for the enzyme catalase if oxygen has been used or is present.
Bacillus
Bacillus subtilis (Gram stain)
Colonies of the model species Bacillus subtilis on an agar plate
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
Rod-shaped gram-positive Bacillus anthracis bacteria in a cerebrospinal fluid sample stand out from round white blood cells, which also accept the crystal violet stain.
Violet-stained gram-positive cocci and pink-stained gram-negative bacilli
Colonies of a gram-positive pathogen of the oral cavity, Actinomyces sp.