Alexander Fleming: the spectrum of penicillin

The discovery of penicillin was directly linked to the inhibition by that agent of the growth of colonies of staphylococcus. However, subsequent resistance by this organism to penicillin as well as to a number of other agents has marked the history of staphylococcus in the antibiotic era. One of the most important mechanisms of this resistance has been the production of penicillinase, an enzyme that inactivates penicillin and related antibiotics. Penicillinase is currently termed beta-lactamase, and it is now recognized that there are several types of beta-lactamases produced by various organisms. The ability of staphylococci to produce this enzyme has been countered by the development of penicillinase-resistant agents and the addition of beta-lactamase inhibitors to antibiotics.