A transportable fluorescence imagining system for detecting fecal contaminants

Feces are the primary source of many pathogenic organisms that can potentially contaminate agricultural commodities. Feces generally contain chlorophyll a and related compounds due to ingestion of plant materials. Fluorescent responses of these compounds to appropriate excitation can mark the presence of feces on animal carcasses, or on fruits or vegetables. We describe a transportable imaging system for detecting fecal contamination. The primary components of the system are a UV light source, an intensified camera with a six-position filter wheel, and software for controlling the system and automatically analyzing images. To test the system, diluted dairy feces were applied to surfaces of red delicious apples using stencils or a pipette. Comparisons of test results using a definitive set of four red-band filters demonstrated that the contrast between fluorescence responses of treated and untreated apple surfaces decreased with increasing wavelength, and was 25% greater at 668 compared to the best results obtained at 678, 685, or 700 nm. Using images acquired at 668 nm, automated algorithms based on either threshold or edge detection were 100% successful in detecting stenciled apples and 1:10 dilution spots applied with pipette, which contained approximately 300 ng of dry matter. In a separate test, sets of feces-treated apples were washed at hourly intervals and then imaged. The contamination sites could not be detected when the contact time was less than 4 h, while 5 h of contact was sufficient to establish consistent fluorescence responses in images. Use of a modified system as a teaching tool demonstrated the robustness of the system and promoted public awareness that fecal contamination invisible to the naked eye can easily be detected with appropriate instrumentation. There are many potential uses for this system, including studying the efficacy of apple washing systems.