All penicillins inhibit the biosynthesis of the bacterial cell wall.
The penicillinase-resistant penicillins are active in vitro against a variety of other bacteria. One such procedure has been recommended for use with discs to test susceptibility to this class of drugs. Interpretations correlate diameters on the disc test with MIC values. A penicillinase-resistant class disc may be used to determine microbial susceptibility to dicloxacillin. A report of resistant indicates that the infecting organism is not likety to respond to therapy.