Answer:
Different antibiotics work differently from each other, some attack bacterial cell wall, some attack proteins, some attack ribosomes and some attack DNA replication machinery.
Antibiotics that attack the ribosomes such as 'tetracycline' actualy inhibit the bacteria to grow by attacking their protein synthesis. Protein synthesis is accomplished in ribosomes, tetracycline cross the bacterial membrane and enter cytoplasm from there i binds on a single specific site on the ribosomes which result in the halting of RNA interaction that stops protein synthesis or extension. In humans, the accumulation of such antibiotics is not to such an extent that it damages the cell machinery.