Bacterial resistance towards antibiotics is increasing. Especially Gram negative (G-) pathogenic bacteria are responsible for serious nosocomial infections. Novel treatment strategies such as antimicrobial photodynamic therapy (aPDT) are needed to fight such infections. G- bacteria are, in general, less sensitive compared to Gram positive bacteria to aPDT as well as other antimicrobial strategies. The aim of the study was to explore drug supersaturation as a mean to “overcome” the outer membrane barrier of G- bacteria in aPDT. Supersaturated solutions were found to be significantly more phototoxic towards G- E. coli compared to solutions at equilibrium. Nanocarriers were selected to create temporarily stabilized supersaturated solutions of the model photosensitizer. Lyophilization of the solutions was then utilized to prepare solid dispersions. The solid dispersions hydrated and dissolved rapidly in aqueous environments and demonstrated promising phototoxic effect towards G- bacteria even at light doses less than 28 J/cm².

Supersaturation and supersaturated drug delivery systems to surpass the outher membrane barriers of Gram negative bacteria in antimicrobial photodynamic therapy (aPDT).
Hegge AB, Vukicevic M, Wikene KO, Bruzell E, Tønnesen HH.
Applications of Nanodrugs in Photodynamic Therapy, Gothenburg April 11-12,  2013 (A)