Going to the mat: Reducing wheel- and foot-borne contamination


by Dr. Caroline S. Clibbon

Two of the most popular flooring options for life science facility entryways are put to the test by Glaxo SmithKline.

For some time it has been established that in order to maintain the highest levels of cleanliness within a classified life-sciences cleanroom, it is essential to prevent the ingress of particles and micro-organisms from the adjoining environment.

The principles of current good manufacturing practices (cGMPs) and quality assurance demand that particle and microbiological contamination levels within any critical area be kept to a minimum to prevent the contamination from corrupting the product. Two major sources of viable and non-viable particle contamination entering critical environments originate from feet and wheels.

The two methods commonly used to reduce foot- and wheel-borne contamination are the “peel-off adhesive mat” and “polymeric” floor covering.

By implication, the application of the cGMP directives in modern life-sciences manufacturing facilities means that the entry into critical environments should be protected to minimize the access of both viable and non-viable particles reducing the microbiological contamination levels.

Both foot- and wheel-borne contamination are two major sources of both viable and non-viable contamination. Controlling or eliminating these particles is paramount as they affect product yield, productivity, quality of the product and cost. Current practice suggests that this contamination can reduce product yield by as much as 20 percent.

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As part of Glaxo SmithKline's on-going policy of “manufacturing for continuous improvement,” research was undertaken to evaluate the two major floor systems commonly used for the progressive reduction and control of particulate contamination from feet and wheels. Since people are a major source of particulate contamination through regenerative processes, operator behavior and work habits, the contamination generated can be easily transferred into the critical areas and cleanrooms on the feet of these personnel or through inanimate objects (cart wheels, materials or equipment).

Therefore, to minimize this particulate contamination, some form of floor-contamination system is essential since it is less expensive and easier to control this contamination prior to the critical environment.

Any method of reducing microbial contamination is welcomed, and the two forms of floor contamination control systems, the “adhesive peel-off mat” and “polymeric flooring” were placed in the pharmaceutical manufacturing unit (PMU) at Glaxo SmithKline, Ware, Hertfordshire, UK, where the work described in this article was carried out. The cleanroom facility in this study is used primarily for water testing with the pharmaceutical microbiology unit.

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The two floor coverings were tested using the swabbing technique: “Dycem polymeric flooring” and “adhesive peel-off mats” were compared. Swabs were moistened with sterile 0.9 percent peptone water (PW) and samples were taken from cartwheels (two wheels from each cart) and the soles of operators footwear at the entry to the corridor area (5F068) of the PMU clean suite (5F069). Swabs were plated out onto Tryptone Soya Agar plates (bacteria) and Sabourand's Dextrose Agar plates (yeasts and moulds) and incubated at 30-35°C and 20-25°C respectively for up to seven days.

Batch information: TSA-N (9cm): 742698701; Incubators; 1 (30-35°C) 2 (20-25°C); SDA (9cm): E23002; PW (9ml): B03100761.

The above procedure was repeated and swabs were taken from cartwheels (two wheels from each cart) after being pushed across the polymeric floor covering and the adhesive peel-off mat. In addition, swabs were taken from operators' footwear after walking across either type of floor covering—making at least six imprints onto the floor covering—and plated out using the procedure described above.

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Experiments were performed under test conditions comparable with those used in practice. The length of polymeric flooring allowed a minimum of at least six footfalls (three for each foot). Swabs were taken from the right foot of operator(s) before taking a minimum of six steps over the polymeric flooring; swabs were then taken from the left foot after stepping over the flooring.

The results were averaged where mean percentages reduction values were calculated. The mean percentage reduction values for the polymeric flooring were 99.4 percent (TSA plates), and 100 percent (SDA plates) for wheel-borne contamination and 99.8 percent (TSA and SDA plates) for foot-borne contamination.

In contrast, the mean percentage reduction values for “adhesive peel-off mats” were 25.2 percent (TSA plates) and 27.15 percent (SDA plates) for wheel-borne contamination and 11.5 percent (TSA plates) and 15 percent (SDA plates) for foot-borne contamination.

These tests and study have demonstrated that polymeric flooring was far more effective in controlling microbiological contamination compared with adhesive peel-off mats for both operators' footwear and cartwheels under the guidelines of this comparison.

Dr. Caroline S. Clibbon is a research microbiologist at Glaxo SmithKline in Ware, Hertfordshire, UK.


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