Elution- The Impossible Task

Elution is the final step in the sampling process before detection can take place. The bacteria are removed from the sampling device and placed in solution for detection or into nutrient broth for pre-enrichment. The fibrous material of the swabs and sponges are designed to capture and retain the bacteria. This feature of the swabs and sponges leads to a significant decrease in the number of bacteria that are removed from the sampling device and put into solution for detection. A large number of pathogens remain in the sampling device reducing the overall proficiency of the sampling method. Sponges and swabs are designed to capture and retain pathogens...getting them off is no small undertaking and in fact, may be impossible.

Finding Pathogens

Location/discovery involves determining the region in which the pathogens might be found and then locating the pathogens within that area with the sampling device. Conventional sampling devices, such as swabs and sponges only effectively sample small surface areas. Swabs and sponges typically are used to sample a 2x2 and 4x4 in area respectively, as recommended by NASA and The American Society for Microbiology’s Clinical Microbiology Procedures Handbook. These small sampling sizes lower the probability of locating and discovering the pathogens within a given area. To make up for the small surface area, more samples are needed to accurately test a given location, subsequently increasing field and laboratory equipment costs and time.
If pathogens are located in a few “hot spots” randomly distributed over a large area, the probability of locating the “hot spots” with swabs or sponges is very low due to the small surface area of individual samples, therefore producing false negatives. This may cause people to be exposed to contamination because the sampling methods allowed the area or objects to be declared free of contamination, when a high level of contamination actually exists.