Biophotometric comparison of cephalexin and cephradine against gram-positive bacteria

We have compared the antibacterial activities of cephalexin and cephradine against Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus (Micrococcus spp. type III), and group B streptococci (35 strains in total), using the Biophotometer. Analysis of growth curves obtained in the presence of various concentrations of the antibiotics revealed little difference between the activities of the two cephalosporins. However, both antibiotics showed maximal activity at 8-16 microgram/ml, and increasing the concentration past this point resulted in a reduced antibacterial effect. Unlike the other species tested, streptococci were not lysed by cephalexin or cephradine.