Unusual Enterobacteriaceae: H2S+ Shigella sonnei, one authentic and one false positive due to contamination with the obligate anaerobe Eubacterium lentum

A mixture of Shigella sonnei and Eubacterium lentum produced H2S in triple sugar iron agar; however, neither produced any in pure culture. A second culture of S. sonnei, isolated in Japan, is thought to be the first documented H2S+ Shigella.