Radiation resistance of microorganisms on unsterilized infusion sets

Three different methods were used for detecting and isolating microorganisms with high radiation resistance from the microbial contamination on infusion sets prior to sterilization. By all three methods, microorganisms with a radiation resistance high enough to be a critical factor in a sterilization process (D-6 value greater-than-or-equal-to 30 kGy) were found with a frequency of approximately two colony forming units (cfu) per 100 product items, even though the product items in two of the series of analyses were irradiated with doses of 3-6 kGy. The frequency of occurrence of isolates with D-6 values greater-than-or-equal-to 30 kGy was 0.45 per 1000 cfu of the total aerobic count. Eight different isolates of microorganisms had D-6 values greater-than-or-equal-to 40 kGy when irradiated in dried laboratory preparation. All but one of these were classified according to morphologic criteria as Deinococcus, and all but one had nonlinear dose-response relationships in semilogarithmic presentation.