[Optical density changes in bacterial protoplast suspensions exposed to membrane-active antibiotics].

The effect of membrane active antibiotics, such as gramicidin S, its derivatives and carbonyl-conjugated pentaens on suspended bacterial protoplasts resulted in lysis of the protoplasts accompanied by a marked decrease in the optical density (OD) of the suspensions. However, when the drug concentrations were lower than those inducing the lysis, an increase in the suspension OD by 10-30 per cent as compared to the control values of the OD was often observed. The increase in the protoplast suspension OD was most pronounced with the use of the drugs with a relatively low lytic activity or under the conditions lowering the lytic activity of the antibiotics. Under such conditions no agglutination of the protoplasts was observed. The comparative estimation of the protoplast diameters by the method of Klenin et al. in the control suspensions of M. lysodeikticus protoplasts and in the suspensions with a stable increase in the OD showed that the OD increase was associated with swelling of the protoplasts: an increase in the suspension OD by approximately 30 per cent corresponded to an increase in the protoplast diameter by approximately 15 per cent. The observed increasing of the suspension OD must be due to the fact that the membrane active antibiotics induced a decrease in the osmotic stability of the protoplasts not sufficient for their lysis.