Hydrogen Sulfide Formation by Shigella alkalescens.

The Shigella are generally regarded as organisms that fail to form hydrogen sulfide. In a recent report on a lead semisolid agar, Friewer and Shaughnessy (Am. J. Clin. Path., 8, 1) observed the formation of H2S by several strains of Shigella paradysenteriae (Flexner) and Shigelka sonnei in this medium and also by the lead acetate paper test, although no mention was made of this reaction by ShigeUa alkalescens. Dr. C. A. Stuart (personal communication) states that he has encountered no alkalescens cultures that produce H2S. During 1945 we isolated 232 strains of Shigella alkalescens in the central laboratory at Jacksonville. Of these, the production of H25 in Kligler's iron agar was noted by 5 cultures. This reaction was not apparent after 24 hours' incubation and was only slight after 48 hours at 37 C, but a very distinct reaction appeared after another 24 hours at room temperature. The first 3 cultures were isolated from routine feces specimens from different persons between May 9 and May 21, 1945. We continued to watch all alkalescens cultures isolated very closely, although H2S was not detected again until September 13, 1945, when it was noticed in a fourth culture. The fifth culture was isolated on October 9, 1945. Since one freshly isolated strain of S. alkalescens has been found by Wheeler et al. (J. Bact., 51, 169) to form acetylnethylcarbinol, others to ferment lactose and sucrose (Stuart and Rustigian: J. Bact., 48, 497) and to lose these characteristics shortly afterwards, it was thought that the ability to produce H2S might also be lost. In January, 1946, the cultures isolated in September and October were forwarded to Dr. Stuart, who found that the reaction, though somewhat weak, was very distinct and also that these cultures contained the antigens A, B, C, and D. One of the cultures found in May was lost. The remaining 2 were checked 7 months after isolation. One strain produced a very distinct reaction after 48 hours, and in 72 hours there was a diffuse blackening in the entire butt of the Kligler culture. The other strain showed no reaction in Kligler's medium, though it is possible the formation would be detected by more sensitive tests. The observation that some strains of Shigella alkalescens form hydrogen sulfide in amounts equivalent to Sa'monella typhi and apparently do not lose this characteristic seemed worthy of note.