This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Haemophilus, Yersinia, Spirochaetes, Ricketssia, Chlamydia, Mycoplasma and Miscellaneous Bacteria), Subject name: Microbiology
Growth factor required for salmonella: 
Select and explain. 
A. Tryptophan, B. Niacin, C. Vitamin B12, D. Citrate
A: Tryptophan
Answer: A: Tryptophan 
Explanation: Salmonella require tryptophan as an essential growth factor. Also remember: Legionella require Iron and Cysteine Mycoplasma require sterols Ureaplasma require sterols and urea Halophilic Vibrio (parahemolyticus) require salt.