The permeability property of the outer membrane of Bacteroides fragilis, a strictly anaerobic opportunistic pathogen.

It was concluded that the exclusion limit of the outer membrane of Bacteroides fragilis is close to the size of uncharged saccharides of Mr, 340-400 and of anionic solutes of Mr, 500 on the basis of the following lines of evidence. Penetration of methylhexoses and salicin into the NaCl-expanded periplasm appeared to be 85 and 50%, respectively, of that of pentoses, whereas penetration of the saccharides of Mr larger than 340-400 was negligibly small. The cells treated with 500 mosM di-through pentasaccharides were about 36% lighter than the isotonic NaCl-treated cells, whereas the 500 mosM pentoses- or hexoses-treated cells appeared to be 16 or 21%, respectively, lighter. The result indicates that the saccharides of Mr more than 340 exerted osmolarity at the outer membrane and hence these saccharides are assumed merely permeable. The phosphorylated solutes and beta-lactam antibiotics of Mr a little larger than the above threshold exclusion limit are partially diffusible.