Bacitracin is a polypeptide antibiotic interfering with the synthesis of peptidoglycan, a unique chemical fabric bacteria include in their cell walls. Bacitracin is common in topical ointments or inhaled into the lungs, but is very rarely given by injection. In a clinical laboratory, bacitracin is useful in helping identify Streptococci and other Gram positive bacteria. Two concentrations of bacitracin-impregnated disks are made for this purpose, with each being useful in distinguishing among select groups of Gram positive cocci.