Effect of pH upon the activity of cefoxitin.

Cefoxitin is a new semisynthetic cephamycin antibiotic, effective against gram-positive and gram-negative bacteria. It is of particular interest because of its activity against cephalosporinresistant strains of Escherichia coli, indole-positive Proteus, Klebsiella and Serratia6) and because of its high resistance to hydrolysis by /J-lactamases3). Antibacterial activities of penicillins and cephalosporins are generally known to increase with decreasing pH of test medium. However, WALLICK and HENDLIN6) reported that there was no appreciable effect of the initial pH of medium on the activities of cefoxitin and cephalothin. We have studied the effect of pH on the antibacterial activity of cefoxitin, and it is apparent that cefoxitin exhibits different characteristics from the other cephalosporins in this respect.