Plasma Decontamination: A Case Study on Kill Efficacy of Geobacillus stearothermophilus Spores on Different Carrier Materials

Abstract

A new technology to the pharmaceutical field is presented: surface decontamination by plasmas. The technology is comparable to established barrier systems like e-beam, volatile hydrogen peroxide, or radiation inactivation of microbiological contaminations. This plasma technology is part of a fully automated and validated syringe filling line at a major pharmaceutical company and is in production operation. Incoming pre-sterilized syringe containers (“tubs”) are processed by plasma, solely on the outside, and passed into the aseptic filling isolator upon successful decontamination. The objective of this article is to present the operating principles and develop and establish a validation routine on the basis of standard commercial biological indicators. Their decontamination efficacies are determined and correlated to the actual inactivation efficacy on the pharmaceutical packaging material.

The reference setup is explained in detail and a short presentation of the cycle development and the relevant plasma control parameters is given, with a special focus on the in-process monitor determining the cycle validity. Different microbial inactivation mechanisms are also discussed and evaluated for their contribution and interaction to enhance plasma decontamination. A material-dependent inactivation behavior was observed. In order to be able to correlate the tub surface inactivation of Geobacillus stearothermophilus endospores to metallic biological indicators, a comparative study was performed. Through consistently demonstrating the linear inactivation behavior between the different materials, it becomes possible to develop an effective and time-saving validation scheme.

LAY ABSTRACT: The challenge in new decontamination systems lies in a thorough validation of the inactivation efficacy under different operating regimes. With plasma, as an ionized gas, a new barrier concept is introduced into pharmaceutical aseptic processing of syringes. The presented system operates in vacuum and only decontaminates the outer surface of pre-sterilized syringe containers (“tubs”), before they are transferred into the aseptic area. The plasma does not penetrate into the tub. This article discusses the phase from development and test germ selection, across the identified sporicidal mechanisms, to a proposal for a validation scheme on the basis of commercially available biological indicators. A special focus is placed on an extensive investigation to establish a link between the tub surface microbial kill (polystyrene and Tyvek^{and 2}) and biological indicator inactivation (stainless steel). Additionally, a rationale is developed on how an optical in-process monitor can be applied to establish a validatable limit on the base of the predetermined inactivation data of Geobacillus stearothermophilus endospores.