“Mycoplasma” describes members of the genus Mycoplasma from the class of Mollicutes, which form a group of tiny, cell-wall less bacteria and comprises over 120 species. They are the smallest self-replicating prokaryotic organisms. Because of their small genome (600-1400 kb depending on the species), Mycoplasmas lack many metabolic pathways and depend on receiving all these nutrients from their environment. Their small size (~ 0.15 μm) allows the mycoplasmas to pass commercially available 0.22- or 0.45-μm sterile filters. In addition, they are resistant to antibiotics such as penicillin and streptomycin.

Common contaminants are: Mycoplasma hyorhinis, Mycoplasma arginini, Mycoplasma hominis, Mycoplasma synoviae, Mycoplasma orale, Mycoplasma fermentans, Acholephasma laidlawii, Mycoplasma pneumoniae, Mycoplasma gallisepticum or the species Ureaplasma urealyticum.

Mycoplasmas are parasitic bacteria that cause many diseases in human, animal and plant. In addition to their pathogenic properties, mycoplasma contamination of cell cultures, cell banks or master cell stock leads to considerable economic or scientific impact: mycoplasmas alters gene expression profiles, metabolism or recombinant protein yield.