Evaluation of a portable test system for assessing endotoxin activity in raw milk

The aim of the present study was to compare endotoxin activities detected in raw milk samples obtained from cattle by a commercially available portable test system (PTS) and traditional microplate limulus amebocyte lysate (LAL)-based assay, which determined activities using a kinetic turbidimetric (KT) assay. Raw milk samples were obtained from 53 and 12 dairy cattle without and with clinical mastitis, respectively. Comparison between the KT and PTS was performed by the Friedman test. The Pearson product moment correlation coefficients were calculated to evaluate associations between any two continuous variables. Linear regression model analysis was also performed to obtain the equation describing the relationship between PTS and KT assay. The endotoxin activities detected in 200- or 400-fold diluted milk samples were similar between PTS and KT assay, whereas a significant difference was observed in 100-fold diluted milk (P<0.001). The results obtained from 200- (r(2)=0.778, P<0.001) and 400-fold diluted milk samples (r(2)=0.945, P<0.001) using PTS correlated with those using KT assay. The median milk endotoxin activities in Gram-positive and Gram-negative clinical mastitis cows were 0.655 and 11,523.5 EU/ml, respectively. The results of the present study suggest that PTS as a simple and easy test to assess endotoxin activity in raw milk is efficient, simple and reproducible.