All work on high contamination risk samples should be carried out in low-DNA laboratory environments. To reduce general environmental DNA contamination and eliminate PCR carryover it is essential that all work on low-DNA samples be carried out in a dedicated laboratory that is physically isolated from other molecular biology laboratories. The general guidelines for such a laboratory are: This laboratory should operate with positive air pressure, HEPA filtered air to prevent influx of micro-organisms, dust, pollen, human hair and shed skin, and overhead germicidal UV lights providing nightly UV irradiation to remove any surface DNA contamination. Laboratory surfaces and equipment should be routinely washed with bleach to remove surface DNA contamination and all equipment and consumables should be purchased new and never have entered another molecular facility. Movement of researchers should always be in a one-way direction, from the clean laboratory to the post-PCR laboratory on any one day. All researchers entering the clean laboratory should wear full body coveralls (including head, arm and leg covering), shoe covers, double gloving, dust or surgical masks and face shields to prevent human and microbial DNA from contaminating the laboratory and specimens.
These issues are fully recognized in the world of ancient DNA studies and though such facilities do not come cheap, they have resulted in the construction of purpose-built, ultra-clean laboratories, routine adoption of stringent procedures for elimination of contaminating sequences from reagents, and an acceptance of the need to validate results in multiple laboratories. Despite a growing number of reports of similar problems in interpretation of data generated by microbial ecology laboratories, similar standards have not yet been universally implemented.
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