EFFECT OF MEDIUM PRESSURE AND LOW PRESSURE ULTRAVIOLET SYSTEMS ON THE INACTIVATION OF SELECTED BACTERIOPHAGES

Four bacteriophages, MS2, phi X-174, T4 and PRD-1 were used to assess the effectiveness of both the low pressure, low intensity (LPLI) and the medium pressure, high intensity (MPHI) ultraviolet light Collimated Beam Units (CBUs) on virus inactivation. Results indicate that bacteriophage MS2 and PRD-1 were the most resistant to UV inactivation when irradiated by both types of UV systems, giving an average D90 value (1 log reduction) at 21 mW sec/sq cm and a k value (inactivation rate) of approximately 0.05 sq cm/mW sec. The most sensitive bacteriophage to UV irradiation was T4, resulting in a D90 at 1 mW sec/sq cm and k value of 0.9 sq cm/mW sec after UV irradiation. The differences in UV susceptibility between the bacteriophages can be due to differences in their nucleic acid characteristics and/or the structural makeup of the virus. The MPHI lamp used has an effective germicidal intensity that is approximately 4 times greater than that measured at 254 nm. Therefore, the exposure time needed to achieve the effective germicidal dose (dose necessary for a desired germicidal effect) is shorter for the MPHI as compared to the LPHI system. Additionally, the similar log survival curves generated by the irradiation of the 4 bacteriophages by the LPHI and MPHI UV lamps suggest that for the MPHI system, wavelengths in addition to that which is emitted at 254 nm is responsible for virus inactivation.