RADIORESISTANCE STUDIES IN METHYLOBACTERIUM SPP

Methylobacterium extorquens was isolated and was found as one of the m ost resistant microorganisms in the original bioburden of ophthalmic c otton dressings to be submitted to gamma radiation sterilization. Radi ation survival curves were simultaneously performed in phosphate buffe r and in test-pieces on two isolates, one obtained before irradiation (wild strain) and the other after irradiation at 20 kGy (rad strain), as well as on three type strains of Methylobacterium spp. (M, extorque ns(T), M. radiotolerans(T) and M. fujisawaense(T)). The radiation resi stance was compared using D-values. To analyze the effect of non linea rity on radioresistance other measures were applied, such as intercept point, fraction of surviving cells at a selected dose and area. The r anking of strains with these approaches showed to be different, pointi ng out the need of an integrated measure of radioresistance. Therefore , an index of relative survival (IRS) is proposed.