[3] Bastian challenges the widely popular theory that the TSEs are caused by prions, which are composed mostly if not entirely of a misfolded form of a protein called PrP (i.e. PrPSc).
He argues instead that the TSEs are caused by an extremely small, cell wall deficient bacterium called Spiroplasma, and that prions are the result of the disease process.
[5] Under his hypothesis, because PrPSc is not the cause it is merely an imperfect marker of infection (with both sensitivity and NPV <1), and is either induced by Spiroplasma directly or by a defence mechanism of the host.
In 2014 he discovered that Spiroplasma forms biofilms which give them significant resistance to radiation, heat, and disinfectants.
He, along with Laura Manuelidis of Yale University, who claims that the TSEs are caused by an as yet undiscovered virus, are two of the main sceptics of the prion theory.