Role of beta-lactamases in the resistance of gram-negative bacilli to beta-lactam antibiotics.

Few studies in animal models or humans have been performed to prove that the mechanism of resistance to beta-lactam antibiotics in the presence of beta-lactamases is similar in vivo and in vitro. In vivo, it seems likely that different parameters will influence each other: the penetration of the antibiotic into the site of infection; the stability of the drug; and the organism responsible for the infection, which affects the type and amount of beta-lactamase released into the environment. In vitro, the different enzymatic parameters responsible for the inactivation of various compounds have been well defined. However, overall resistance to beta-lactams in the presence of beta-lactamase may also be influenced by the function of the outer membrane in gram-negative bacteria.