Molecular cloning of the gene of a penicillin-binding protein supposed to cause high resistance to beta-lactam antibiotics in Staphylococcus aureus

Abstract

A novel penicillin-binding protein, PBP-29 (Mr about 75,000), is known to be induced in excessively large amount by most beta-lactam compounds in cells of a clinically isolated strain of Staphylococcus aureus, TK784, that is highly resistant to beta-lactams and also most other antibiotics. This protein has very low affinities to most beta-lactam compounds and has been supposed to be the cause of the resistance of the cells to beta-lactams. A 14-kilobase DNA fragment was isolated from the cells that carried the gene encoding this penicillin-binding protein and also a genetically linked marker that is responsible for the resistance to tobramycin. This DNA was cloned on plasmid pACYC184 and was shown to cause both production of PBP-29 and resistance to tobramycin in Escherichia coli cells. However, the formation of PBP-29 in E. coli was only moderate and was independent of normal inducer beta-lactams. The PBP-29 formed in the E. coli cells showed slow kinetics of binding to beta-lactams similar to that of PBP-29 formed in the original S. aureus cells and gave a similar pattern of peptides to the latter when digested with the proteolytic V8 enzyme of S. aureus. Images