Gram-positive bacilli belong to a class of rod-shaped bacteria that acquire a violet color when subjected to the Gram staining method. Aside from its characteristic shape, this class of bacteria has a thick peptidoglycan layer, which lends itself to better absorption of antibiotics.
Many Gram-positive bacilli have caused numerous diseases around the world. Mycobacterium tuberculosis causes severe lung disorders and is transmitted through the air by sneezing or coughing. Listeria monocytogenes is a facultative bacteria species that causes listeriosis, one of the primary causes of meningitis and meningoencephalitis. Mycobacterium leprae infection in humans results in Hansen's disease, more commonly known as leprosy. Bacillus anthracis is the main agent of anthrax, the fatal disease considered a bioterrorism threat in 2001 when bacterial spores were delivered in regular mail.
In contrast, some Gram-positive bacilli are safe for humans and are even infused in food. Bacillus subtilis is a spore-forming bacteria used in manufacture of the Japanese food natto and is also used in antibiotics to treat urinary tract infections.
Gram staining is a bacterial differentiation method that categorizes various species of bacteria according to their response to a violet stain. This procedure relies on the absorption of a crystal violet dye by the bacteria's peptidoglycan layer, a layer present only in Gram-positive bacteria.