An agar plate is a sterile Petri dish that contains agar plus nutrients, and is used to culture bacteria or fungi.ypes of agar plates [edit]. 1  Blood agar-contains blood cells from an animal (e.g. a sheep). 2  Most bacteria will grow on this medium. 3  Chocolate agar-this contains lysed blood cells, and is used for growing fastidious (fussy) respiratory bacteria. 4  Neomycin agar-contains the antibiotic neomycin.