In vitro inhibition of Neisseria gonorrhoeae growth by a urogenital strain of Streptococcus faecalis

Abstract

A strain of Streptococcus faecalis isolated from the urogenital flora was selected for its ability to inhibit the in vitro growth of Neisseria gonorrhoeae. Initially, the inhibitory activity was demonstrated on solid medium only when the inhibitor and the target strains were growing simultaneously, such as in the spot-lawn and flip-flop agar overlay methods. The antigonococcal effect was not due to a shift in the pH or depletion of nutrient in the medium. This activity was not produced in liquid medium nor could it be extracted in a soluble form from either the solid medium or the streptococcal cells. The production of the inhibitory activity could not be enhanced by ultraviolet irradiation or treatment with mitomycin C. The composition of the medium was found to affect the size of the inhibitory zone produced. The inhibitory activity showed a wide antigonococcal spectrum and was susceptible to trypsin and pronase but resistant to alpha- and beta-amylases and catalase. This activity passed through a filtering membrane and was also dialyzable and had an apparent molecular weight of less than 1,000. The addition of bovine serum albumin to solid medium enabled us to show an inhibition even when the producer and the target strains were grown sequentially, thus suggesting that part of the difficulty of studying such inhibitory activity could be due to its instability.