A sensitive photometric pyrogen assay.
Ein empfindlicher photometrischer Pyrogentest
One of the biocompatibility criteria for implants and invasive devices is the absence of pyrogens at their surface. Currently the assay to measure such surface contaminations is the printing of these surface-attached microorganisms onto culture plates, and, after prolonged incubation, counting of the number of colonies that develop on a particular growth medium. For small parts such as needles or tubes etc. this is difficult to carry out. Mixed contaminations or fragments of bacteria can be detected with a pyrogen assay which utilizes the coagulation of a limulus hemolysate in the presence of small numbers of gram negative bacteria. In the course of developing a very sensititve assay for detection of microorganisms in highly purified water we have improved a commercially available pyrogen test procedure. With the kinetic evaluation of photometric long term incubations we can reach a detection limit of <0.05 ng/l of a standard pyrogen corresponding to 0.5 international endotoxin units p er litre. Also a convenient concentration procedure was developed which allows to concentrate up to 5000-fold solutions with low pyrogen contents. With this test procedure we can measure the surface related contamination of biomaterials such as membranes or injection shunts etc. by washing microorganisms off the surface and measure the pyrogen content in the concentrated solution or incubate the device directly.