Endotoxin measurement in house dust using the end-point Limulus amoebocyte lysate method

Endotoxin is a lipopolysaccharide, a part of gram-negative bacteria cell membrane commonly present in general and many occupational environments. This paper describes sample preparation and endotoxin measurement in 16 samples of house dust from urban homes (Zagreb, Croatia) using end-point chromogenic Limulus amoebocyte lysate (LAL) bioassay. House dust was collected on cellulose filters by vacuuming bedroom and living room floors, and was kept frozen until assayed. Samples were extracted from filters with a 0.05% solution of Tween-20 in endotoxin-free water. Serial dilutions of samples were measured in duplicates. The linearity of the standard curve was satisfying (r=0.983), as well as the recovery (92 and 110%) and repeatability (coefficient of variation from 0 to 8.5%). The endotoxin levels found in the house dust samples ranged from 4.8 to 200 EU/mg, with the arithmetic mean of 49.5 EU/mg (standard error of the mean of 12.1 EU/mg), and were in the range of house dust endotoxin values obtained by other authors.