Studies on anti-osmotic stability of bacterial membrane lipids by carboxyfluorescein release.

I have developed a method for measuring the anti-osmotic stability of liposomes prepared with lipids extracted from bacteria, using the release of carboxyfluorescein trapped in liposomes as an indicator. I also examined the sub-second physical changes of liposomes submerged in a solution of low osmotic pressure with a stopped flow spectrophotometer. The trapped carboxyfluorescein was released when the liposomes burst upon the inflow of excess water. Liposomes prepared with the lipids of a stable S. aureus L-form strain or Mycoplasma orale were more resistant to osmotic pressure than those prepared from the wild strain of S. aureus. It was found that cardiolipin enhanced the membrane-stability in S. aureus and cholesterol (about 30% of the total membrane lipids) in Mycoptasma orate. By the present method, the resistibility of membranes to low osmotic pressure could be determined precisely with extracted and purified bacterial membrane lipids.