This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Anatomy
Diphtheria antibody titer considered optimally protective is 
Select and explain. 
A. >0.1 IU/ml, B. >0.01 IU/ml, C. >0.05 IU/ml, D. 0.5 IU/ml
A: >0.1 IU/ml
Answer: A: >0.1 IU/ml 
Explanation: Diphtheria antibody titer considered as optimally protective is >0.1 IU/ml. Titers of IgG antibody against diphtheria toxoid vaccine reflect various levels of protection against the disease as follows: <0.01 IU/ml: No protection 0.01 IU/ml: Basic protection >0.1 IU/ml: Optimal protection. Ref: Textbook of microbiology; Ananthanarayan and paniker's; 10th Edition; Pg; 245