The Acetate Differential Slant is formulated with the base formula of Simmons Citrate Agar, but sodium citrate is replaced with sodium acetate. Differentiation is based on the organisms ability to utilize acetate. Approximately 84% of E. coli species utilize acetate, whereas the majority of Shigella species are incapable of acetate utilization.(5) 7.7% Shigella flexneri 4a, mannitol +, and 86% Shigella flexneri 4a, mannitol -, are capable of utilizing acetate