Thursday, July 22, 2010

The Role of Glasses in Aseptic Production: A Detail Often Ignored

Hood, suit, faceplate, cover shoes, gloves: these are the necessary items of clothing when operating in A- and B-grade areas. The principal purpose of protective clothing is to minimize the risk of microbiological contamination caused by personnel. Thus, protective garments should not release fibers and must be able to contain particles produced and released by the body.

But how can we ensure that protective garments are not themselves vehicles of contamination? And how can we ensure that cleaning and sterilization processes are effective and do not alter the characteristics of the garments? We attempted to answer these questions, concentrating our attention mainly on glasses (in general, on individual protection devices usually referred to as masks).

Because glasses are not disposable, we must consider that stress conditions such as repeated sterilizations may compromise their use. The glasses may lose functionality and the components might be damaged, resulting in the release of contaminating material.

Figure 1: The type of glasses evaluated
We prepared a study protocol to help verify the following aspects:
  • the glasses' ability to endure repeated sterilization processes without suffering alterations;
  • the ability of the sterilization process to obtain a 12-log reduction of the starting microbiological charge.

We chose to verify only the steam-sterilization cycle because it is the process most commonly used in the pharmaceutical industry, although glasses also are sterilized using other methods (γ-rays, ethylene oxide, etc.).

Table I: Characteristics of the glasses used.
For our tests, we used glasses (see Figure 1) with the characteristics outlined in Table I. Tests were conducted to verify that it was possible to subject glasses to repeated sterilization cycles without any alterations that could compromise their usefulness. Glasses in the trial were subjected to repeated steam sterilization cycles (temperature = 121 ± 1 °C, time = 30 min) according to the outline in Table II. At the end of the fixed sterilization cycles, the glasses were evaluated for adherence to the facial conformation, lens transmission, and particle release.

The effectiveness of the sterilization process is a probabilistic function depending on the number of microorganisms present, the thermic resistance of these microorganisms, and the quantity of heat supplied. Therefore, determining the quantity of heat that is necessary to attain the 12-log reduction in the microorganism population to ensure sterility depends entirely on the thermic resistance of the present microorganisms.

Table II: Glasses subjected to steam sterilization cycles.
The thermic resistance of the microorganisms was evaluated by verifying the D value as the time necessary to reduce 90% of the population of present microorganisms (1 log) in specific sterilization conditions. Even if the sterilization cycle recommended by the producer is a typical overkill cycle, it is necessary to evaluate the D value of the microorganism in a trial because this value strongly depends on the possible interactions between the microorganisms and the material on which they are found.


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