Penicillin is the archetypal beta-lactam antibiotic. This antibiotic family has a chemical structure dominated by a beta-lactam ring, hence the name. Examples of beta-lactam antibiotics include penicillins, cephalosporins, carbapenems and monobactams. These have been the most widely used antibiotics in human medicine. The beta-lactam antibiotics bind to the penicillin-binding proteins of the bacteria and prevent cell wall synthesis. Therefore, the bacteria dies. Bacteria have developed a number of mechanisms of defense against beta-lactam antibiotics. One of these is production of enzymes, known as beta-lactamases, which destroy the beta-lactam ring and inactivate the antibiotic. Addition of a beta-lactamase inhibitor to the beta-lactam antibiotic has been partially successful in alleviating this resistance. Some bacteria (for example, MRSA) have developed mutated penicillin-binding proteins and thus have developed resistance to all of the beta-lactam antibiotics (except the newest cephalosporin antibiotics, ceftobiprole and ceftaroline).