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
Safety pin appearance is shown by-a) Hemophilus ducreyib) Chlamydiac)  Donovani granulomatisd) Mycoplasma 
Select and explain. 
A. a, B. ac, C. ad, D. b
B: ac
Answer: B: ac 
Explanation: Bipolar staining (safety pin appearance) 

Some bacteria display a safety pin appearance due to the accumulation of dye at the poles of the cells.


This characteristic is called bipolar staining.


Bacteria showing bipolar staining are-


Calymmatobacter granulomatis (Donovani granulomatis)
Pseudomonas mallei
Pseudomonas pseudomallei   
Vibrio parahemolyticus
Yersinia pestis
H.ducreyi