Why are cells arrested with colchicine during metaphase of mitosis when creating a karyotype?

Because at metaphase stage of cell division that is when chromosomes are highly condensed. addition of colchicine inhibits the formation of spindle fibers and this will prevent separation of sister chromatids which will arrest the cells at the stage of metaphase. during this stage, chromosomes are organized in X-shape and are therefore easier to score.

To kill bacteria from our body especially from stomach