Summary: The rates of hydrolysis of carbenicillin and of other penicillins and cephalosporins by nine different β-lactamase preparations obtained from Gram-negative bacteria were compared. Enzymes produced by Klebsiella strains, most active against penicillins, as well as β-lactamases synthesized by and strains hydrolysed carbenicillin, although at relatively lower rates than ampicillin or cephaloridine. In contrast, carbenicillin was extremely resistant to β-lactamases with a predominant cephalosporinase activity as produced by and Enterobacter strains. The cephalosporin β-lactamases activity of these enzymes was inhibited by carbenicillin. A considerably increased enzymic activity observed in one strain of when grown in the presence of carbenicillin or other β-lactam antibiotics was unable to destroy carbenicillin to any measurable extent. A possible permeability barrier to carbenicillin has been demonstrated in some strains.


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