STUDIES ON THE "CARRY-OVER" OF ANTIBIOTICS USING THE CELLOPHANE TRANSFER TECHNIQUE

The cellophane transfer technique has been used in the clinical laboratory as a guide to combined treatment and also to study the bactericidal actions of all common antibiotics, but during recent work it became clear that some antibiotics are absorbed on to the cellophane and enough may be carried through on to the fresh medium to inhibit growth of survivors even after transfer. The present investigation has been made to determine the maximum concentrations which can be used without risk of inhibition by carry-over Certain concentrations are recommended and also the depth of agar, and with this there should be no risk of invalidating these bactericidal tests by bacteriostatic inhibition of survivors of carry-over. In clinical studies it is usually only necessary to test one of each group of antibiotics. That showing least carry-over should be used.