The Effect of Membrane-bound -Lactamase on Linoleic Acid Sensitivity in Staphylococcus aureus

Microbiology Unit, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, U.K. ABSTRACT SUMMARY: The presence of a plasmid conferring resistance to penicillin (PC plasmid, e.g. pI 258 bla I - ) in Staphylococcus aureus NCTC 8325 increases the sensitivity of such a bacterium to the growth inhibitory effects of linoleic acid, whereas a plasmid conferring resistance to tetracycline does not affect linoleic acid sensitivity. The increased linoleic acid sensitivity of bacteria containing a PC plasmid may be related to the penicillinase protein itself since (i) strains having inducible penicillinase show increased sensitivity only after induction, (ii) strains in which penicillinase is directed from chromosomal or plasmid-borne genes show similar increased linoleic acid sensitivity and (iii) notwithstanding the above, the linoleic acid inhibitory effect is enhanced in a strain in which penicillinase activity is greatly reduced by a point mutation in the structural gene for penicillinase. The enhanced linoleic acid sensitivity seems to require the membrane-bound penicillinase since added extracellular penicillinase does not confer this sensitivity, and there appears to be a specific interaction between the membrane-bound penicillinase activity and linoleic acid. Present address: Microbiology Department, Life Sciences Building, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, U.K.