Action Of Membrane Active Antibiotics On The Survival Of X-Irradiated Escherichia Coli B/R
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Abstract
When E. coli strain B/r was X-irradiated in the presence of oxygen and incubated immediately after irradiation in a non-lethal concentration of penicillin, significant additional killing of the cells was observed. It was concluded that the observed enhanced killing was due to an interaction of penicillin and X-rays at the specific site of action of penicillin, since radiation energy is believed to be deposited randomly within the cells. The critical lesions probably occurred in the membrane moiety. In this study, membrane active
antibiotics were substituted in place of penicillin.
Polymixin B sulphate and Cerulenin showed similar effects as penicillin but not Tetracyline. It was therefore suggested that the latent radiation induced lesion can be detected by a range of membrane perturbing agents and the enhanced lethality observed does not depend entirely on the specific action of penicillin. On the extent of enhanced killing, penicillin showed a larger oxygen enhancement ratio from 2.8 to 4.9 compared to Polymixin 2.8 to 3.9 and Cerulenin from 2.8 to 3.8. The additional killing observed in penicillin was possibly through a combination of induction of filaments and direct membrane damage. However, in terms of the concentrations of these antibiotics required to cause the oxygen dependent membrane damage, Penicillin was 17M while Polymixin required 16M. Cerulenin on the other 3 hand, required about 10 M to achieve the same level of inhibition. Polymixin and Penicillin were about equally effective on exposing the membrane damage while Cerulenin was the least effective of the antibiotics used. The significance of this findings in relation to better understanding of the mechanisms of radiation damage is discussed.
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