I had a culture grown on PDA medium which is producing red colour and it is a guess that it is a mixed culture of some actinomycete and some bacteria, can anybody suggest using some technique for how best I can separate them?
i would suggest you to go for serial sub culturing in respective meium for actinomycetes use actinomycetes isolation agar or some ISP medium and for normal bacterial species use LB medium.
Serial dilution will help if the culture is of bacterial origin. If your pure culture is fungus then overlay your contaminated culture with PDA the fungus will grow over and bacterium will not. Then use Single spore technique to pure the culture once again.
Go with serial dilution upto 10 rasie -3to -5 or more and then do subculture on Plate count agar , soyabean casein digest agra for bacteria , PDA for fungus or specific media or into PDA add chlorophenicol antibiotic to pinch, it suppress the bacterial flora .
try to make a mix culture on PDA plate than inoculate bacteria on separate plate by identifying nature of bacteria and media selection. For which have to need morphological identification of culture in media. You can use an indicator media for that and distinguish desirable strain of bacteria and preferable make single colony culture by selection of media each time.