DNA replication is necessary for bacterial cell replication. One of the ways that antibacterials are effective is by inhibiting the DNA replication. Antibacterials often accomplish this by:
1. Encouraging the replication of the original DNA to form a new DNA strands.
2. Encouraging migration of the DNA strands to opposite sides of the cell.
3. Affecting the enzymes needed for DNA replication.
4. Assisting the supercoil to relax and unwind

Replication is the process by which cells duplicate their genetic material (DNA or deoxyribonucleic acid) before undergoing the process of cell division so that each copy of the duplicated DNA is incorporated in each of the daughter cells produced after the process of mitosis (cell division).
The parent bacteria also transmit their genetic material to the daughter bacteria by the same process.
There are many enzymes required for the process of DNA replication:

DNA polymerase : synthesizes new daughter DNA strand.
Helicase: unwinds the parental DNA double helix.
Toposiomerase: uncoils the DNA supercoils.
Primase: synthesize short fragments of RNA, called Primers, those provide the 3' hydroxyl group for the purpose of nucleotide addition by DNA polymerase.
Ligase: anneals the Okazaki fragments generated on the newly synthesized lagging DNA strand.

Antibacterials target to kill (bactericidal) or prevent the growth (bacteristatic)of bacteria.
This is possible by inhibiting the process of replication in the bacteria.
Replication can be inhibited by inhibiting any of the above enzymes which are necessary for the operation of the replication process in the correct manner.