Bacitracin is a mixture of related cyclic peptides produced by organisms of the licheniformis group of Bacillus subtilis var Tracy, first isolated in 1945. These peptides disrupt both gram positive and gram negative 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). While the use of any antibiotic can contribute to antibiotic resistance, localized topical applications are less frequently implicated than their systemic counterparts. However, antibiotics such as bacitracin have been shown to act as dermatological irritants and may slow healing.