For  example, penicillin and its related compounds prevent susceptible  bacteria from creating a cell wall. They do this by binding to and  inactivating an enzyme (transpeptidase) necessary for the cross-linking  of peptidoglycan in the wall, thus stopping its formation. Resistance to  this antibiotic is due to the bacteria producing its own enzyme called  beta-lactamase which breaks the ring structure of the penicillin and  prevents its ability to bind to the bacterial transpeptidase.