Hi: You can use antibiotic (Agromycine) in the medium , just mix the antibiotic after autoclaving the medium and the medium shouldn't be hot.

If you don't want to use antibiotics, split medium in the Petri dish in two using some sterile plastic barrier. Fungal mycelium will grow through medium to the other side and bacteria should stay on the surface.

You can use a specific media for Trichoderma = Trichoderma-selective agar medium (TSM)

http://link.springer.com/article/10.1007/BF03158330

Thank you very much everybody ( Oadi Matny, Adam Dawidziuk, Bhavin Mehta, Laith Al-Ani) .