Influence of substrate materials on inactivation of B. atrophaeus endospores in a reduced-pressure argon plasma

Abstract

High disinfection level/sterilization of medical devices (MDs) can be achieved through plasma immersion in an argon discharge operated at reduced pressure (100 Pa). The plasma source is a high-frequency (HF) discharge from our laboratories. The power density absorbed in this system is low enough to allow the continuous processing of thermally-sensitive materials. Bacterial B. atrophaeus endospores are deposited either on glass or polystyrene (PS) Petri dishes and thereafter subjected to the argon discharge. The role of these substrates in the spore inactivation process is analysed by means of spore survival curves and through examination by a scanning electron microscope of possible structural damage to the spore morphology. In addition, optical emission spectroscopy (OES) is performed in the presence of the glass and PS Petri dishes in the discharge, and modifications to the surface characteristics of the exposed substrates are evaluated by contact angle measurements and X-ray photoelectron spectroscopy (XPS). It is found that: (i) inactivation of spores is less effective when they are deposited on PS substrates; (ii) spores deposited on glass are eroded while those on polystyrene are left almost morphologically intact; (iii) the OES spectrum from the discharge is not affected when glass substrates are introduced into it, whereas the presence of PS substrates strongly modifies it; (iv) exposed PS substrates show surface modifications, as revealed by contact-angle measurements and XPS analysis; (v) the presence of air impurities in the discharge, even at very low levels, seems to play a key role in the inactivation process, in particular by leading to the generation of UV photons. The results obtained underline the need for a thorough evaluation and control of the materials from which the MDs are made. The discharge interacts with the polystyrene Petri dish, modifying the plasma gaseous phase and affecting the properties of the substrate surface. The VUV/UV radiation spectrum and intensity then available for inactivation are also affected. Viable micro-organisms are removed from the substrate by the discharge and disseminated, contaminating the chamber and the 'outside world' through the pumping outlet. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.