The major difference between human and bacteria cells is that bacteria cells have Cell Wall. Each bacterium is surrounded by the wall to keep its shape.
Many antibiotics kill bacteria by damaging their cell walls.
※ Human cells do not have cell wall and so are not damaged by these antibiotics.

     In bacteria, the cytoplasm referring to everything to survive contains numerous ribosomes that are involved in protein synthesis. Therefore, many antibiotics work to kill bacteria by inhibitingprotein synthesis.
　　※ Because human ribosoms are different from bacteria’ and so are not damaged by these antibiotics.

     Some antibiotics, Quinolones, Sulphonamides, and Rifampicin etc., work by inhibiting nucleic acid synthesis.
There are two kinds of nucleic acids, DNA and RNA. They are generally produced in the central region of the bacteria cell continuously