PEPTIDOGLYCAN TRANSPEPTIDASE INHIBITION IN PSEUDOMONAS-AERUGINOSA AND ESCHERICHIA-COLI BY PENICILLINS AND CEPHALOSPORINS

Peptidoglycan transpeptidase activity has been studied in cells of E.coli 146 and P. aeruginosa 56 made permeable to exogenous, nucleotide-sugar peptidoglycan precursors by ether treatment. Transpeptidase activity was inhibited, in both organisms, by a range of penicillins and cephalosporins, the Pseudomonas enzyme being more sensitive to inhibition in each case. Conversely, growth of E.coli 146 was more susceptible to these antibodies than growth of P.aeruginosa 56. Furthermore, similar transpeptidase inhibition values were obtained for the 4 penicillins examined against the Pseudomonas enzyme, although only two of these (carbenicillin kand pirbenicillin) inhibited the growth of this organism. It is therefore concluded that the high resistance of P. aeruginosa 56 to growth inhibition by most β-lactam antibodies cannot be due to an insensitive peptidoglycan transpeptidase.