Compositions, reaction mixtures, kits and methods used in amplifying and detecting nucleic acids from various species of the class Mollicutes. Particular regions of the 23S rRNA or its gene have been identified as preferred targets for nucleic acid amplification reactions of a sample suspected containing at least one species of Mollicutes. Some oligomers comprise tag regions, target closing regions, promoter sequences, and/or binding moieties. Samples can be from any source suspected of containing a species of the class Mollicutes. Preferred sample sources include bioreactors, cell lines, cell culture wares and pharmaceutical manufacturing wares.