A typing scheme for Neisseria gonorrhoeae
Growth of gonococci in vitro was studied during an attempt to find a typing scheme for epidemiological purposes. Many strains were found to be capable of remaining viable for several weeks in a liquid medium formulated particularly to prolong survival in laboratory cultures. Gonococcal strains were found to survive even longer when they were kept in liquid culture media at 30°C which is known to be their minimal growth temperature. The feasibility of using gonococcal bacteriocins (the gonocins) in typing gonococci was investigated, and was found to be impracticable, because some inhibitory short-chain fatty acids were observed to interfere with, and to dominate, the inhibitory activity of gonocins. These fatty acids were found by gas-liquid chromatographic analysis mainly to be acetic acid and isovaleric acid. When these two acids were added to uninoculated media in concentrations equivalent to what was produced during the metabolic activity of gonococci, some gonococcal strain s were inhibited on that media. The Colicins of Shigella sonnei were found to be possible substitutes for gonocins. Ten Colicin Type strains inhibited gonococci selectively. Thus it was possible to divide ninety two strains into groups on the basis of their sensitivity to the colicins. Certain limitations made it difficult to evaluate this typing scheme fully. Yet some indication was given that it could be a useful tool for epidemiological studies. In spite of the high stability of colicinogeny of Shigella sonnei strains, some inhibitory by-products might accumulate in the medium when the Colicin Type strains were incubated for four days. In this way the inhibitory activity of colicins against gonococci might increase. But by gas-liquid chromatographic analysis it was found that the by-products, namely acetic and propionic acids, which were produced after incubating the Colicin Type strains for one day were not adequate to cause misinterpretation of the activity of colicins. These by-products however, might accumulate after prolonged incubation and reach an inhibitory concentration which interfered with the colicin activity. It was demonstrated that Colicin Type strains used in the typing scheme should be incubated for not longer than one day.