Abstract
Comparison of endotoxin exposures reported by various authors is problematic since sampling and analytical methods have not been standardized. As part of a study of respiratory hazards in the turkey growing industry, replicate samples from two types of barns (brooder and hen grower) were assayed by two laboratories using different Limulus-based methods. One set of samples was assayed using the kinetic Limulus assay with resistant-parallel-line estimation (KLARE) method, and the other set was assayed using a conventional chromogenic endpoint Limulus amebocyte lysate (LAL) method. Possible sources of disagreement included: changes during shipping; different extraction methods; sample dilutions; lysate preparations; response; and data analysis. Use of different control standard endotoxins in the two laboratories resulted in significantly different estimates when computed as nanograms of endotoxin. When results were calculated in endotoxin units relative to U.S. Reference Standard Endotoxin EC-5 the methods were not different overall, although they did differ significantly in one barn. Both methods detected a significant difference between barns and ranked them in the same order. Airborne concentrations of viable gram-negative bacteria, however, ranked the barns in the opposite order. It is probable that both LAL-based methods detected only endotoxin released from the cell wall of gram-negative bacteria. These data show that the two LAL methods, while in general agreement, did not behave in the same manner in similar environments, although there was no evidence of interferant compounds. These discrepancies may help to explain why some authors found a strong correlation between airborne endotoxin and respiratory health, and others did not. Future epidemiologic studies should employ more than one method and should compare the relative utility of various methods for predicting the respiratory toxicity of inhaled endotoxin.
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Stephen J. Reynolds
Reynolds, S.J.; Milton, D.K.: Comparison of Methods for Analysis of Airborne Endotoxin. Appl. Occup. Environ. Hyg. 8(9):761–767; 1993.