cis-9,10-Methyleneoctadecanoic acid is a cyclopropane fatty acid that has been found in bacteria and the digestive gland of P. globosa. It is a component of S. aureus cell membranes and levels decrease upon treatment with carvacrol. cis-9,10-Methyleneoctadecanoic acid is secreted by H. pylori and enhances histamine- and dibutyrylcAMP-stimulated acid secretion in isolated guinea pig parietal cells. It also activates protein kinase C (PKC) in a calcium-dependent manner.