Cloning and expression of genes responsible for altered penicillin-binding proteins 3a and 3b in Haemophilus influenzae

Abstract

A Haemophilus influenzae strain (T-1,3) possessing clinical beta-lactam resistance due to altered penicillin-binding protein 3 was used to construct a recombinant cosmid gene bank in Escherichia coli. Three of the recombinant cosmids were capable of transforming a susceptible H. influenzae strain (Rdnov) simultaneously to moxalactam resistance and altered the binding of penicillin-binding proteins 3a and 3b to [35S]penicillin G. Restriction endonuclease mapping of one of the recombinant cosmids, pLB100, was performed to facilitate subsequent subcloning of the gene(s) responsible for the altered penicillin-binding protein 3 (a and b) binding phenotype. Subcloning of individual fragments derived from pLB100 indicated that two adjacent fragments of DNA were both capable of transforming a susceptible Haemophilus strain to moxalactam resistance and altered penicillin-binding protein 3 binding. Expression of plasmid-coded proteins in minicells indicated that one fragment coded for a major 55,000-molecular-weight polypeptide and that the second contained a C-terminal coding region that expressed a 28,000-molecular-weight polypeptide when fused to the N-terminal region of the tetracycline resistance gene. Initial attempts at labeling the plasmid-coded proteins expressed in minicells with [35S]penicillin G were unsuccessful.