Detection of bacterial contamination BChE contaminated with bacteria migrates more slowly on a nondenaturing gel stained for BChE activity. Lanes 1-3, human serum; lanes 4-5, highly purified human BChE, 800 EU/ml; lanes 6-7, partially desialylated BChE; lanes 8-9, completely desialylated human BChE by bacterial contamination 30,000,000 EU/ml; lanes 10-11, completely desialylated human BChE , by treatment with viral neuraminidase; lanes 12-13, purified horse BChE from Sigma, 800 EU/ml; lanes 14-15, horse serum. Each lane contains the amount of BChE enzyme activity in 5 microliters of human serum, 0.015 units.