The effect of methicillin on the fatty acid composition of total polar lipid in methicillin resistant Staphylococcus aureus.

The effect of two concentrations of methicillin on the fatty acid (FA) distribution in intracellular total polar lipid (TPL) of the log-phase cultures of a methicillin resistant Staphylococcus aureus strain No. 5814R was studied during a period of 2 h. Half the MIC of methicillin (= 1000 micrograms/ml) caused 18.6% increase in branched-FAs and a same decrease in straight-FAs, while one MIC (= 2000 micrograms/ml) of the drug induced a moderate change in those of TPL. The ratio of branched-FAs to straight-FAs increased from 1.24 to 1.56 in the presence of 1/2 x MIC of methicillin and reduced from 1.24 to 0.87 in the presence of 1 X MIC of the antibiotic. In TPL of the control cultures it gradually decreased from 1.24 to 0.77. It is concluded that under the effect of methicillin, FA composition of TPL in methicillin resistant cocci does not change as dramatically as in methicillin sensitive ones indicating lipid synthesis in methicillin resistant S. aureus to be less sensitive to the action of methicillin than in methicillin susceptible strains. This may contribute to the resistance against the lytic effect of the drug. Membrane lipid properties seem to be involved in the mechanisms of methicillin resistance.