Use of Cellulose Acetate Membranes for detecting Penicillinase-producing Organisms

Abstract

DURING investigations into the gain or loss of penicillinase in cultures of staphylococci¹ there was a need for a simple method of screening these so as to be able to detect small numbers of penicillinase positive or negative organisms in mixed cultures. In addition, in the study of hospital cross-infection a quick reliable method was required for investigating many different strains of staphylococci for penicillinase production. A number of chemical and microbiological methods for detecting the ability of organisms to destroy penicillin have been described^2–7. However, none of the methods in common use is really adapted for the study of mixed penicillinase-positive and negative populations on the surface of solid media, nor is it easy to use them so as to detect a few colonies of one type in the presence of a predominant growth of the other. One of the most useful diagnostic methods for pour plates is that described by Manson, Pollock and Tridgell⁸. We have modified their method by pouring agar containing penicillin and Andrade's indicator gently over colonies growing on the surface of agar plates, but under these conditions the method is not so sensitive nor so reliable as when deep cultures are used.