This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
All are true about Rickettsia except ? 
Select and explain. 
A. obligate intracellular, B. Gram +ve bacillus, C. Ahropods are vector, D. Weil felix test is diagnostic
B: Gram +ve bacillus
Answer: B: Gram +ve bacillus 
Explanation: Ans. is 'b' i.e., Gram +ve bacillus Rickettsiae are Gram negative Pleomorphic coccobacilli Obligate intracellular organisms Non motile Non capsulated Stain bluish purple with Giemsa and Castaneda stains Stain deep red with Machiavella and Gimenez stains About other options . Rickettsiae are transmitted to humans by ahropod vectors through their bite or feces . Serological diagnosis of Rickettsial infection may be done by . Heterophile Weil felix reaction or . Specific tests using Rickettsial antigens.