Liberation of endotoxin from Escherichia coli by addition of antibiotics.

The liberation of endotoxin from Escherichia coli by the addition of antibiotics was investigated using a new method of limulus test, i.e. dry up method. The addition of the bactericidal antibiotic, aminobenzylpenicillin or streptomycin sulfate, to the suspension of Escherichia coli (about 10(6)/ml) increased the concentration of endotoxin in the suspension about eight to nine times during a 3-hour period after the addition of antibiotic accompanying with the concomitant decrease of viable cell counts. The addition of the bacteriostatic antibiotic, tetracycline hydrochloride, also increased the endotoxin level, but this increase was rather mild. On the other hand, in the case of the addition of polymyxin B sulfate, there was no evident increase of the endotoxin level. This ability of polymyxin, i.e. the ability to suppress the elevation of endotoxin levels, was shown when polymyxin in the concentration of more than 2.5 micrograms/ml was added against about 10(6)/ml Escherichia coli and was also shown by the combinational use of polymyxin with aminobenzylpenicillin or streptomycin. Furthermore, the endotoxin-inactivating ability of polymyxin was shown in the study where extracted lipopolysaccharide was used in place of viable cells.