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Journal of Clinical Microbiology, 10 1995, 2643-2646, Vol 33, No. 10
DL Wiedbrauk, JC Werner and AM Drevon
The detection of viral nucleic acids in intraocular fluids and tissues by
PCR has become increasingly important in clinical ophthalmology. While much
attention has been directed toward minimizing false-positive reactions
resulting from specimen contamination or amplicor carryover, relatively
little attention has been given to the causes of false- negative PCRs. This
report describes a PCR inhibitor in normal aqueous and vitreous fluids that
can produce false-negative PCR results. As little as 0.5 microliter of
vitreous fluid and 20 microliters of aqueous fluid can completely inhibit
DNA amplification in a 100- microliters PCR mixture. This inhibition was
not primer specific, nor was it due to chelation of Mg2+ ions or DNase
activity in the ocular fluid. The inhibitor was completely resistant to
boiling for 15 min. However, the inhibitory effects were completely removed
by a single chloroform-isoamyl alcohol (24:1) extraction. The extent of PCR
inhibition depended upon the type of thermostable DNA polymerase used in
the reaction. Taq DNA polymerase was very sensitive to the inhibitor, while
thermostable DNA polymerases from Thermus thermophilus HB-8 (Tth) and
Thermus flavus (Tfl) were completely resistant. Thus, the inhibitory
effects of intraocular fluids on PCRs can be removed by diluting the
specimen, by chloroform extraction, or by using Tth or Tfl DNA polymerases.
Copyright © 1995 by the American Society for Microbiology. All rights reserved.
Inhibition of PCR by aqueous and vitreous fluids
Department of Clinical Pathology, William Beaumont Hospital, Royal Oak, MI 48073-6769, USA.
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