A Model System to Demonstrate That -Lactamase-Associated Antibiotic Trapping Could Be a Potential Means of Resistance

Abstract

Addition of β-Iactamaseto cultures of antibiotic-sensitive Escherichia coli protected the bacteria against lysis induced by either a hydrolyzable (cephalothin) or relatively nonhydrolyzable (ceftriaxone) cephalosporin. The later addition of a nonhydrolyzable, non-lysis-inducing β-Iactam antibiotic (oxacillin), which had a higher affinity for the β-Iactamase than ceftriaxone, allowed the reversal of the protection and the onset of lysis. These results suggest that trapping of the antibiotic by the enzyme, without significant hydrolysis, is a reversible process that may playa role in the resistance of some gram-negative bacteria to third-generation cephalosporins.