Laboratory studies on mecillinam: activity alone and combined with cephradine.

Mecillinam (MC) was found to be inhibitory at low concentrations to a wide range of Gram-negative bacteria; the sensitivity of such strains could be predicted by using a 10 microgram disk. Resistance to MC did not appear to be associated with beta-lactamase-mediated destruction of the antibiotic. Ampicillin-resistant strains tended to be less sensitive to MC. MC and cephradine acted synergistically against Proteus mirabilis, Pr. vulgaris, Prov. stuartii and Serratia marcescens, and the combination was additive against most Klebsiella aerogenes, Enterobacter spp. and Escherichia coli.