A Microphotometric Method for the Estimation of Penicillinase in Single Bacteria

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Abstract
A microphotometric technic is described by which the penicillinase content of a single bacterium in a stable microdrop is measured. The microdrop contains a buffer, benzyl-penicillin and bromocresol-purple. As the penicillinase hydrolyzes the penicillin to penicolloic-acid, the concentration of the cationic (purple) form of bromocresol-purple decreases. This decrease is measured by a specially designed single-beam microphotometer, and, from the change in light transmission and the volume of the drop, the total penicillinase content of the drop is calculated. The microphotometer and the calibration of the assay with soluble penicillinase preparations are described.