Antibiotics affect the growth of bacteria by inhibiting the production of substances which are required for the bacterial growth.
Due to which the life cycle of the bacteria is affected, and the bacteria becomes dead.
If we use excessive antibiotics, then the bacteria present in our intestine which are helpful in our body for synthesis of some important nutrients like vitamins also get affected.
Death of these bacteria due to excessive use of antibiotics causes deficiency of vitamins in our body.