RESULTS OF COMPARATIVE EXPERIMENTS USING DIFFERENT METHODS FOR DETERMINING THE SENSITIVITY OF NEISSERIA GONORRHOEAE TO PENICILLIN G.

Between 1957 and 1960 a decrease in the sensitivity of Neisseria gonorrhoeae to penicillin was observed in many parts of the world, but the ranges of sensitivity and the distribution of strains within these ranges varied in different countries. It was not known, however, whether these differences were real or due to the different methods of sensitivity determination used. The collaborative study described in this paper was sponsored by WHO with the object of developing an international reference method for use in epidemiological and interlaboratory studies. Fourteen gonococcal strains, representing a wide range of sensitivity to penicillin, were tested in the three participating laboratories, using two plate dilution methods and a tube dilution method. When the strains were arranged in order of sensitivities, the order was the same whichever method was used, but the levels of sensitivity showed considerable differences, particularly for the less sensitive strains. Good agreement was obtained when the technique of one laboratory was repeated in another. On the basis of the results, it is recommended that an international reference method should use a plate dilution technique and a provisional medium is suggested for this method. It is probable that better agreement between different methods could be achieved by the use of reference strains which would enable a correction factor to be applied. Three gonococcal strains that might prove suitable for this purpose are suggested.