In the projected video showing the growth of bacteria, why did the bacteria grow up to the edge of the area with antibiotics, pause, then continue to grow across the area with antibiotics?

A number of bacteria witness random mutation in their DNA, this random mutation allows some if them to grow regardless of the presence of antibiotics.

Explanation: When antibiotics are misused or over-used,some bacteria develop resistance to the antibiotics,so during a culture,the bacteria tends to grow in the presence of the antibiotics it is resistant to because of the DNA of the bacteria is altered in the nucleotide sequence of the genome( haploid chromosome).