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.
release of carboxyfluorescein
bacterial membrane lipids