Answer: Human immunodeficiency Virus.
Explanation:
According to Koch postulates the The microorganisms can be grown on pure culture( postulate 2).
But the human immunodeficiency virus cannot be grown on pure culture. Without a suitable not human host a researcher cannot evaluate postulate 2.
Human immunodeficiency virus needs host cell to grow it does not use any other animal as a host cell so this virus does not follows Koch postulates.