Effect of pH on inhibition of plasmid-carrying cultures of Staphylococcus aureus by lipids.

The inhibition of Staphylococcus aureus by fatty acids was pH dependent. The inhibitory properties of myristic acid were greater at pH 5.5 than at pH 7, whereas those of linoleic acid were less at pH 5.5 than at pH 7. Seven clinical penicillin-resistant cultures survived better in the presence of linoleic acid at pH 5.5 than did their sensitive counterparts. The resistance to linoleic acid in most plasmid-carrying cultures at pH 5.5 was probably not due to the production of penicillinase, but to some other determinants carried by the plasmid.