Holup, you raise an interest point. A true sanitize cycle is heat. It gets hit enough to kill everything.
How the fuck is a plastic toilet cleaning brush surviving the level of heat sufficient to kill all bacteria?
If the original dishwasher from the past for got enough to kill bacteria, the brush couldn’t survive. Therefore, the dishwasher isn’t getting hot enough to kill bacteria. Therefore don’t put poopy plastic into your dishwasher!