For this study, a population of 1.3×106 Geobacillus stearothermophilus spores inoculated onto paper strips wrapped in Tyvek were utilized. Tyvek is comprised of flash spun non-directional polyethylene, which makes it not only durable, but also porous. These microscopic pores are too minute for not only the indicator microbes residing inside the Tyvek to escape, but also for any microbes and particulate outside of the Tyvek to penetrate. Gaseous CD molecules and water vapor however, are easily able to maneuver in and out of these pores.
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Explore This IssueApril/May 2014
As a result of this combination, this BI is capable of not only validating a 6-log sporicidal reduction, but can also be used as a tool in determining CD’s penetrability through organic loads.
Gaseous CD Decontamination
For this study, a ClorDiSys Minidox-M gaseous CD generator was utilized to automate the five step decontamination process in an effort to reduce human error.
Earlier studies have confirmed that the following cycle ensures a 6-log reduction of spore forming bacteria. Though these studies were conducted under controlled conditions, they indicate the baseline for which to gauge penetration of gaseous CD through the organic loads used in this study.
Upon loading and executing the standard decontamination cycle on the Minidox-M generator, “Pre-condition” is initiated. During this step, the chamber’s relative humidity (RH) is raised by a humidifier inside the chamber. Through continuous monitoring, via an RH/temperature probe, the Minidox-M effectively regulates humidification until the predetermined RH set point is reached. Once satisfied, the generator initiates “Condition,” whereby the 65 percent RH residing inside the chamber is maintained and resupplied accordingly for 30 minutes. “Condition” is critical in promoting the susceptibility of bacterial spores to the gaseous CD.
Subsequent to “Condition”, the Minidox-M initiates the CD gas injection step referred to as “Charge.” CD gas is injected, sampled, and monitored in real-time until it reaches its predetermined concentration of 1 milligram/liter (mg/L). Upon reaching its set point, injection ceases and “Exposure” begins. Just as this step’s name implies, all contents located inside the chamber are exposed to the recently injected CD gas. During “Exposure,” humidity and CD concentration are continuously monitored in real-time and respectively supplied to the chamber when either falls under their set points. This phase persists until 720 ppm-hrs (parts per million-hours) has accumulated, or 120 minutes of 1 mg/L contact time has lapsed.
Powdered milk, powdered baby formula, protein powder, flour, sugar, grain, and general dust/dirt were selected to simulate organic loads that are commonly seen in food processing facilities. A set of three Geobacillus stearothermophilus populated Tyvek-wrapped BIs consisting of 1.3 x 106 spores were assigned to each of these six varieties. Each set was dusted so that the Tyvek side of each BI was covered not only in its entirety, but also generously enough for the identifying text to no longer be visible.
A 17.0 foot3 polypropylene isolator was utilized as the chamber to conduct this study. The isolator was equipped with various ports and cables for the Minidox-M generator and a carbon scrubber to interface with. Each covered set of three BIs and a single set of three uncovered control BIs were placed inside the isolator along with a small fan, a humidifier, and a probe that monitored both RH and temperature. The RH/temperature probe was connected to an interfacing cable inside the isolator, which was then connected outside to the generator. Similarly, the humidifier was connected to a relay that sat just outside of the isolator, which was then connected to the generator for humidification control. The small fan was plugged into an outlet located inside the isolator and energized to speed up gas distribution. A 0.375-inch CD gas injection tube and a 0.25- inch gas sample tube were then connected on opposite sides of the isolator to avert any false sample readings during the cycle.