Interaction of a new cephalosporin, 7-cyanacetamidocephalosporanic acid, with some gram-negative and gram-positive beta-lactamase-producing bacteria.

When gram-negative beta-lactamase-producing bacteria were incubated at 37 C in broth containing 100 to 250 mug or more of 7-cyanacetamidocephalosporanic acid (CAA) per ml, a red or orange color developed, irrespective of whether or not growth had occurred. This color development was paralleled by breakdown of CAA by Escherichia coli R(+)TEM, although there was a concurrent lethal effect on the cells. No red color developed with gram-positive or gram-negative strains that did not produce beta-lactamase. Several methicillin-susceptible beta-lactamase-producing strains of Staphylococcus aureus produced a faint red color, as did one of four penicillin acylase-producing E. coli strains. No color resulted when two methicillin-resistant, beta-lactamase-nonproducing S. aureus strains were tested. Two methicillin-resistant, beta-lactamase-producing S. aureus strains produced a bright red color at 37 C, but a much fainter one at 30 C.