Carotenoid pigment levels in Staphylococcus aureus and sensitivity to oleic acid

Staphylococcus aureus mutants lacking pigment, or expressing only low levels of pigment, were more sensitive to oleic acid than were the parent strain and mutants making more pigment than the parent. One class of mutants (colour index 5), although possessing significant levels of pigment, were nevertheless quite sensitive to oleic acid. This suggested that only certain carotenoids in the biosynthetic pathway were capable of imparting resistance to fatty acids. The phenotypic expression of pigment also affected the sensitivity of a strain to oleic acid. The parent S. aureus strain 18Z, when grown to express its maximal pigment potential, was more resistant to oleic acid than when it was grown to express minimal levels of pigment.