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 milksamples obtained from cattle by a commercially available portable test system (PTS) andtraditional microplate limulus amebocyte lysate (LAL)-based assay, which determinedactivities using a kinetic turbidimetric (KT) assay. Raw milk samples were obtained from53 and 12 dairy cattle without and with clinical mastitis, respectively. Comparisonbetween the KT and PTS was performed by the Friedman test. The Pearson product momentcorrelation coefficients were calculated to evaluate associations between any twocontinuous variables. Linear regression model analysis was also performed to obtain theequation describing the relationship between PTS and KT assay. The endotoxin activitiesdetected 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-(r²=0.778, P<0.001) and 400-fold dilutedmilk samples (r²=0.945, P<0.001) using PTScorrelated with those using KT assay. The median milk endotoxin activities inGram-positive and Gram-negative clinical mastitis cows were 0.655 and 11,523.5EU/ml, respectively. The results of the present study suggest that PTSas a simple and easy test to assess endotoxin activity in raw milk is efficient, simpleand reproducible.