This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
Proteus antigen cross react with: 
Select and explain. 
A. Klebsiella, B. Chlamydiae, C. Rickettsiae, D. E. coli
C: Rickettsiae
Answer: C: Rickettsiae 
Explanation: Ans. 'c' i.e., Rickettsiae(Ref: Ananthanarayan, 9th/e, p. 410)Proteus antigens (OX19, OX2, OXK Strains) cross reacts with group specific alkali stable lipopolysaccharide rickettsial antigens. The application of this property is done in the Weil Felix (heterophile agglutination) test.