Bacitracin is used mainly as a topical treatment for Superficial skin infections caused by Staphylococcus aureus Polymyxin B and colistin have rapid concentration-dependent bactericidal activity against Most facultative and aerobic gram-negative bacilli, including Pseudomonas aeruginosa and Acinetobacter species These drugs are not active against Proteus, Providencia, Burkholderia, and Serratia species and some obligate anaerobes, including Bacteroides fragilis and gram-positive bacteria (1).