Polycations increase the permeability of Mycobacterium vaccae cell envelopes to hydrophobic compounds

Polycations [protamine, polymyxin B nonapeptide (PMBN) and polyethyleneimin e (PEI)] have been shown to increase the cell wall permeability of Mycobact erium vaccae to highly hydrophobic compounds, as manifested in enhanced int racellular bioconversion beta -sitosterol to 4-ndrosten-3,17-dione (AD) and 1,4-androstadien-3,17-dione (ADD), and cell sensitization to erythromycin and rifampicin. The quantity of AD(D) formed per biomass unit was twice as high in the presence of PMN and PEI, and three times higher with protamine. The sensitization factor, i.e. the MIC50 ratio of the control bacteria to those exposed to polycations, ranged from 4 to 16, depending on the polycat ion/antibiotic combination. Non-covallently bound free lipids were extracte d from the control and polycation-treated cells and fractionated with the u se of chloroform, acetone and methanol. Chloroform- and acetone-eluted frac tions (mainly neutral lipids and glycolipids, respectively) showed signific ant polycation-induced alterations in their quantitative and qualitative co mposition. The fatty acid profile of neutral lipids was reduced in comparis on to control, whereas acetone-derived lipids were characterized by a much higher level of octadecenoic acid (C-18:1) and a considerably lower content of docosanoic acid (C-22:0), the marker compound of mycolate-containing gl ycollipids. Methanol-eluted fractions remained unaltered. Cell-wall-linked mycolates obtained from delipidated cells were apparently unaffected by the action of polycations, as judged from the TLC pattern of mycolic acid subc lasses, the mean weight of mycolate preparations and the C-22:0 acid conten t in the mycolates, determined by GC/MS and pyrolysis GC. The results sugge st the involvement of the components of non-covalently bound lipids in the outer layer in the M. vaccae permeability barrier.