Determination of endotoxins on hypodermic needles by means of a chromogenic Limulus amoebocyte lysate assay. Development of a test model.

A test model was developed in order to describe the determination of endotoxins on hypodermic needles in a reliable and reproducible manner. As in all in-vitro experiments one has to be very careful about extrapolating data to in-vivo situations. However by choosing a hydrophilic (Salmonella typhimurium ATCC 14028) and a hydrophobic bacterium (Acinetobacter calcoaceticus var. anitratus RR 8212/113), one could hope to obtain a quite representative idea about the extraction of contaminating gram-negative micro-organisms. Using the proposed extraction procedure and a chromogenic LAL assay as detection system, it was possible to achieve a quantitative idea about the extraction of endotoxins on hypodermic needles. Extracting needles at 19 degrees C during 83 to 98 min produced the highest yield as to the detection of endotoxins from hydrophilic strains. For the detection of endotoxins from hydrophobic strains, the highest yield values were obtained when the extraction was performed at temperatures between 64 and 80 degrees C during 96 to 120 min. However it seems necessary to perform the extractions at least three times in order to obtain reproducible results. In conclusion, using the extraction procedure as described, it is possible to measure endotoxin-like activity, on the inner and outer surface of hypodermic needles in a simple but accurate way, using water as extraction fluid and a chromogenic Limulus Amoebocyte Lysate assay as detection system.