Bacteria is a cell, antibiotics kill these bacteria (cell). Human body is also made of cells, how does it affect our body?
Bacteria consist of cell walls and antibiotics are the drugs which are used to break down the cell walls of bacteria causing their lysis. For example: An antibiotic, Penicillin blocks the action of the cross-linking enzyme transpeptidase, so although cell wall subunits are produced normally, they are not cross linked to one another. This cross-linking failure creates weak bacterial cell walls which break down very easily and the cell lyses, killing the bacteria. While human beings dont have cell wall, so antibiotics dont affect them.