The Role of Penicillin Acylase in the Resistance of Gram-Negative Bacteria to Penicillins

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Abstract
SUMMARY: The resistance of 148 clinical isolates of Gram-negative bacteria to ampicillin and benzylpenicillin was determined in serial-dilution sensitivity tests, together with the extent of inactivation of the penicillins, and the production of 6-aminopenicillanic acid (6-APA). Many of the cultures were resistant to the penicillins and inactivated the compounds, but only one culture, a strain of Escherichia coli, showed penicillin acylase activity, as indicated by the production of 6-APA. However, the cultural conditions prevailing in serial-dilution tests, namely, stationary culture at 37°, although favourable for the functioning of penicillin acylases, were shown to be highly unfavourable for production of the enzyme by coliform bacteria.