on some of my plates after streaking and incubation, I could observe growth at the periphery of my agar plates.
I wonder wether this was contamination.
One problem I had was that the agar shrank during the incubation. For this reason, I soaked paper tissue with tap water and put it and the agar plates into a plastic bag. I sealed the bag and incubated. the agar did not shrink anymore.
Another problem is that the agar rotates against the petri dish. Before incubation I draw a line on the bag of the dish to divide it into to halfs. Then I inoculate each half with one bacterial species. After incubation it might happen that the streaks of inoculation crosses the lines of the petri dish. The agar seems to have moved.
Could anyone help me out with these two issues?