penicillinase

penicillinase /pen′əsil″ənās/ , an enzyme elaborated by certain bacteria, including many strains of staphylococci, that inactivates penicillin and thereby promotes resistance to the antibiotic. A purified preparation of penicillinase, derived from cultures of saprophytic spore-forming Bacillus cereus, is used in the treatment of adverse reactions to penicillin. Also called beta-lactamase.