Cyclacillin: in vitro activity against aerobic and anaerobic bacteria.

Cyclacillin at 50 microgram/ml inhibited streptococci (100%), shigella (72%), and Bacteroides (B) fragilis ss fragilis (84%). At 100 microgram/ml it inhibited proteus (75%), B. fragilis (86%), and E. coli (50%). Cyclacillin was more effective than ampicillin against beta-lactamase-producing H. influenzae. The activity of cyclacillin was found to be more enhanced when tested in nutrient agar and Mueller-Hinton agar than in brain heart infusion agar.