Cross-reactivity with food products, fungal growth, and acid phosphatase testing
Ostapovicz, Katrina F.
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Testing potential semen stains on items of evidence typically involves detection of acid phosphatase (AP), commonly through the use of the AP Spot test. However, other substances are known to produce AP, including common fungi. This suggests that the presence of fungal growth in a sample, either through improper evidence storage or contamination at the scene, may cause a false positive result with the AP Spot test for semen, as it is not specific to seminal acid phosphatase. This study examines the AP activity of various food, paper, plant, and non-semen biological samples both with and without mold growth, as well as that of known mold culture samples. Each sample was deposited onto individual filter papers and five drops of AP Spot test solution were added. The samples were monitored for 5 minutes, and an AP-positive result was indicated by a color change to violet or pink-violet. All strongly positive samples were then tested using ABAcard® p30 immunochromatographic assays for the presence of protein p-30 (p30) and RSID™-Semen immunochromatographic assays for the presence of semenogelin (Sg). The AP Spot test showed strong positive results, in the form of a dark, intense color change to violet or pink-violet, in non-moldy cremini mushrooms, portobello mushrooms, shitake mushrooms, white mushrooms, pears, bananas, and butter bread. Positive AP Spot test results were also obtained for nine additional non-moldy food products. Sixteen foods gave positive AP Spot test results following the development of mold. All mold culture samples showed strong positive results with AP Spot test. Among the non-semen human biological samples tested, nearly all exhibited a positive color change, though oftentimes faint. Following mold growth on 15 of these samples, all gave a positive reaction with two urine samples, one saliva sample, and one vaginal secretions sample showing a more intense color change than before mold growth. All p30 and Sg testing yielded negative results, even when AP results were positive. This study demonstrates that a variety of foods, yeast and mold have detectable levels of acid phosphatase in the absence of semen using the AP Spot test. This study also demonstrated that semen-free moldy samples with detectable levels of acid phosphatase did not yield positive p30 or Sg testing results. Thus, evidence that has developed mold or come into contact with mold spores or certain food products should be interpreted with caution when positive AP Spot test results are obtained and may warrant subsequent immunological and microscopic testing.