Innovation in Biological Indicator Evaluator Resistometer Vessel Technology - Pharmaceutical Technology

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Innovation in Biological Indicator Evaluator Resistometer Vessel Technology
The authors examine advances in the design and the application of biological indicator evaluator resistometer vessels used to measure the resistance of bacterial spores in monitoring sterilization processes.

Pharmaceutical Technology

In steam sterilization, exposure of samples to the sterilizing conditions may need to be extremely brief, especially when determining the resistance of bioburden isolates. Unfortunately, the insertion and removal of samples can alter the conditions of the test. The majority of BIER vessels use extremely small chambers for various reasons:

  • Small chambers are all that are required to evaluate limited numbers of spore strips and inoculated components products.
  • A small chamber is more easily brought to and from the desired sterilizing conditions. (An adjacent larger chamber is sometimes used as a reservoir for the sterilizing medium.)
  • Smaller chambers are easier to maintain uniformly within the desired conditions.

Figure 2
Figure 2 shows a commercially available BIER vessel used for steam sterilization D-value determination. The use of a small chamber for the BIER has inherent limitations. The BIER vessel cannot be used for any other purpose. The expenditure of a substantial sum (approaching $100,000) for a single piece of equipment having only limited use as a BIER is certainly prohibitive. For this reason and perhaps no other, BIER vessels only are found at biological indicator manufacturers and some of the very large pharmaceutical firms.

The intent of the Fedegari FOB series design was to provide BIER capabilities meeting ANSI/AAMI/ISO 18472:2006 requirements in a fully functional laboratory sterilizer (1). This would allow major advantages over existing BIER vessels:

  • When not used as a BIER, it could function as a steam sterilizer
  • The availability of a steady state chamber provides typical BIER performance
  • Based on a standard autoclave, it could be produced at a substantially lower price.

Figure 3
There were several other goals for the design: conversion from autoclave to BIER and back again without tools in less than 5 min, no adverse impact on the performance of the unit as a standard sterilizer, easy-to-use controls, and a simple gravity feed and discharge mechanism. These goals were accomplished by relatively minor modifications to the standard Fedegari FOB laboratory sterilizer (see Figure 3).

The Fedegari FOB laboratory sterilizer has several characteristics that make it ideally suited for use as a combination BIER and sterilizer. It has an internal circulating fan, driven by a magnetic coupling, which aids in distributing the sterilizing medium. It is rated for full vacuum and up to 3.5-bar internal pressure. It comes with a liquid-ring vacuum pump and is equipped with its own dedicated steam generator, thereby eliminating lengthy pipe runs. It also includes a highly capable process controller that can be integrated with a personal computer or network for data upload.

The Fedegari BIER system is available in several variations:

  • As a fully configured laboratory sterilizer with or without its own steam supply
  • As a field retrofit to an existing Fedegari FOB sterilizer
  • As a field retrofit to an existing steam or gas sterilizer from any manufacturer
  • As a hybrid BIER incorporating combined steam or gas capability in a single unit.

The ANSI/AAMI/ISO 18472:2006 standard entitled Sterilization of Health Care Product—Biological and Chemical Indicators: Test Equipment specifies "the requirements for the test equipment to be used to establish the response of chemical and BIs to critical process variables" (1). This article presents the parametric data collected on the Fedegari resistometer and compares it with this standard. In addition, the performance of the resistometer was evaluated (using BIs as a tool) by direct comparison with two Steris-manufactured resistometers.


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