Question

Penicillin does not have any effect on humans. It only inhibits the growth of bacteria. (Information given in a question)
Then how does it not affect the good bacteria present in our body and thereby affect us?

Answer 1

Antibiotics do have an impact on the gut flora which is maintained by harmless strains of bacteria. Along with the harmful strain, the harmless strains also gets killed which is why during any ailment where the causative agent is bacteria it is advised to take curd to replenish the gut flora.