Bacitracin is a polypeptide antibiotic. It is a mixture of related cyclic peptides produced by Bacillus licheniformis bacteria, that was first isolated from the variety "Tracy I" (ATCC 10716) in 1945. These peptides disrupt Gram-positive bacteria by interfering with cell wall and peptidoglycan synthesis. Bacitracin is primarily used as a topical preparation, as it can cause kidney damage when used internally. It is generally safe when used topically, but in rare cases may cause hypersensitivity, allergic or anaphylactic reactions, especially in patient allergic to neomycin. Medical uses Bacitracin is used in human medicine as a polypeptide antibiotic and is "approved by the U.S. Food and Drug Administration (FDA) for use in chickens and turkeys," though use in animals contributes to antibiotic resistance. As bacitracin zinc salt, in combination with other topical antibiotics (usually polymyxin B and neomycin) as an ointment ("triple antibiotic ointment," with the brand name Neosporin), it is used for topical treatment of a variety of localized skin and eye infections, as well as for the prevention of wound infections. A non-ointment form of ophthalmic solution is also available for eye infections. Although allergic cross-reaction with sulfa drugs has been occasionally reported, bacitracin-containing topical preparations remain a possible alternative to silver sulfadiazine (Silvadene) for burn patients with a sulfa allergy. Bacitracin can also be bought in pure form for those with allergies to the usual polymyxin B and neomycin components of the combination product. Bacitracin is also commonly used as an aftercare antibiotic on tattoos and circumcision. It is preferred over combination products such as Neosporin because of its fewer ingredients, which lowers chances of an allergic reaction. In 2005–06, it was the sixth-most-prevalent allergen in patch tests (9.2%). It was voted Allergen of the Year in 2003 by the American Contact Dermatitis Society. In infants, bacitracin is rarely administered intramuscularly for the treatment of staphylococcal pneumonia and empyema when due to organisms shown susceptible to bacitracin. This use is extremely limited, since bacitracin is nephrotoxic and its concentration in the blood must be followed closely. Bacitracin can be used to distinguish Streptococcus pyogenes from other streptococci, with S. pyogenes being sensitive to bacitracin and others resistant. In this case bacitracin is used to distinguish S. pyogenes from other β-hemolytic streptococci. It is also commonly used to distinguish Haemophilus influenzae colonies amongst respiratory flora; since H. influenzae is intrinsically resistant to bacitracin, colonies form within the zone of