Activity of cefazolin against dense populations of enterobacteria

The in vitro activity of cefazolin was assessed by continuous turbidimetric monitoring of cultures of gram-negative bacilli and the results were compared with those previously obtained with other beta-lactam agents using the same strains and methods. Cefazolin was found to induce rapid lysis of ampicillin-susceptible and -resistant strains of Escherichia coli at a lower concentration than any other beta-lactam agent tested; its stability to beta-lactamase, as judged by regrowth studies, was generally considerably greater than that of other antibiotics of this group. Tested against 103 ampicillin-resistant enterobacteria, cefazolin was found to be more active than cephalothin against E. coli, but no systematic increase in susceptibility to cefazolin was seen with other species. A study of cefazolin in an in vitro model which simulates the hydrokinetic features of the urinary bladder showed it to be as active as ampicillin against ampicillin-susceptible E. coli and as active as cephalothin against ampicillin-resistant E. coli.