Living animals with immune systems are the only types of organisms which can effectively host pathogens such that they can be communicated. Even your example belies the problem: pus is produced by the immune system destroying bacteria, it isn't a bacterial colony itself.

In an a bioreactor where no immune system exists, there can't be a latent infection: there's no immune system! If it can infect and destroy what's growing, then it'll infect and destroy all of it. It isn't going to look like tuna meat after that.