Effect of methicillin on the phospholipid content of methicillin sensitive Staphylococcus aureus

The effects of methicillin at concentrations of 1 microgram/ml (= 1/2 x minimum inhibitory concentration) and 2 microgram/ml (= 1 x MIC) on the phospholipid content of methicillin-sensitive Staphylococcus aureus 5814S growing exponentially were studied. During 2-hour treatment 1/2 x MIC of methicillin induced a significant increase in the phospholipid content of the cocci; accumulation of acid phospholipids was prevalent. In contrast, addition of 1 x MIC of methicillin to the cultures resulted in significantly less phospholipids in the cocci compared with that of the control cultures. There were some alterations in the amounts of individual phospholipids during treatment. The phosphatidic acid (PA) and diphosphatidylglycerol--cardiolipin (DPG) contents were significantly reduced in the first hour then reached the control values by the end of the 2nd hr of exposure. An opposite change was found in the amount of lysylphosphatidylglycerol (LPG), whereas the phosphatidylglycerol (PG) level was significantly lower in the treated cultures than in the controls of corresponding age. Phospholipid synthesis seems to be one of the sites of the action of methicillin in S. aureus.