The signature 10‐hydroxy stearic acid thought to correlate with infectivity in oocysts of Cryptosporidium species is an artifact

Heating or freezing leads to loss in infectivity of oocysts of Cryptosporidium parvum toward neonatal BALB/c mice and is reflected in the profile of the polar lipid fatty acids. Upon loss of infectivity, the ratio of polar lipid to neutral lipid fatty acid decreased and the relative proportions of 18∶1n‐9 also decreased; proportions of 18∶2n‐6 and 20∶5n‐6 increased, whereas the proportions of 16∶0 remained constant with freezing. During these investigations, a novel fatty acid, 10‐OH 18∶0, was discovered in the glycolipid fraction. The identification of a fatty acid unique to species of Cryptosporidium was thought to provide a specific biomarker for this organism. Cryptosporidium also demonstrated fluctuations in absolute quantities of 10‐OH 18∶0 with events that lead to loss of infectivity. This led to the presumed correlation of this biomarker with infectious Cryptosporidium. The 10‐OH 18∶0 was putatively localized at the sn‐2 position of phosphatidylethanolamine. High‐performance liquid chromatography/electrospray ionization mass spectrometry revealed that the 10‐OH 18∶0 existed principally in the free fatty acid form. Herein, we establish that the free fatty acid 10‐OH 18∶0 was, in actuality, an artifact of the procedures for sample preparation.