Salmonella species are characterized by all except:: (A) Acid and gas production from fermenting glucose, (B) Citrate synthesis, (C) H2S production, (D) Indole negative
Answer is B. Ref: Colour Atlas and Textbook of Medical Microbiology, Elmer W Koneman, 5th edition. Pages 186.195Explanation:Citrate is typically utilized as a sole source of carbon by Salmonella species, but not synthesized, as is given in this option.CITRATE UTILIZATION TESTPrinciple: To determine the ability of an organism to use citrate as the sole source of carbon for metabolism and growth.Contents o NaCl.o MgSO4.o Ammonium di hydrogen phosphateo Sodium citrateo Distilled watero Agar.o Bromothymol blue as indicator.Procedure: A light inoculum is inoculated on to the surface of the citrate medium.Interpretation:o Production of blue colour after 24 hours incubation at 35CC indicates positive citrate utilization test.Positive citrate test seen in:o Klebsiella spp.o Citrobacter sppo Salmonella typhimurium.If it remains green colour-- it is negative. Eg. E. eoli. Salmonella Typhi.(Remember--Salmonella Typhi and Salmonella paratyphi A are always citrate negative, while all the other Salmonella are citrate positive.)Salmonella usually show the following key reactions:o KIA-Alkaline slope/acid butt with gas and hydrogen sulphideo MR positiveo VP-negative.o Citrate utilization positiveo Urease negative.o Utilize Lysine. Ornithine and Arginineo ONPG-negative.