Sulbactam is a molecule which is given in combination with beta-lactam antibiotics to overcome beta-lactamase, an enzyme produced by bacteria that destroys the antibiotics. Sulbactam is an irreversible inhibitor of beta-lactamase; it binds the enzyme and does not allow it to interact with the antibiotic. Sulbactam is able to inhibit the most common forms of beta-lactamase but is not able to interact with the ampC cephalosporinase. Thus, it confers little protection against bacteria such as Pseudomonas aeruginosa, Citrobacter, Enterobacter, and Serratia, which often express this gene. In the United States, sulbactam is combined to form cefoperazone/sulbactam and ampicillin/sulbactam.