The present invention relates to a method for determining contaminations in a cell culture sample comprising the steps of: a) contacting a sample of a cell culture suspected to comprise contaminations with a composition comprising oligonucleotides under conditions which allow for amplification of polynucleotides, wherein said oligonucleotides comprise oligonucleotides of at least three different groups of oligonucleotides, and b) determining the contaminations based on the amplified polynucleotides obtained by using the oligonucleotide groups of step (a). Moreover, the invention relates to a composition comprising an oligonucleotide mixture. Further encompassed by the present invention is a composition comprising a probe oligonucleotide mixture. Finally, the present invention also relates to kits comprising said oligonucleotide mixtures.