Establishment of double- antibody sandwich ELISA for detection of EHEC O157 in food

The polyclonal antibody of Enterohemorrhagic Escherichia coli O157( EHEC O157) Ig G was prepared by intravenous injection into New Zealand rabbit with inactivated engineered bacteria E.coli O157 Δler/stx( p BR322: :stx1 /2B: : eae).A double-antibody sandwich ELISA was developed to detect E.coli O157 in food samples,which using polyclonal antibody Ig G as the capture antibody,and monoclonal antibody 2H9 against main virulence factors of EHEC O157 as the detection antibody.Linear equation of standard curve was y = 0.3479x-0.4121,R²= 0.9862,and variation coefficient less than 5%. The detection limit of this sandwich ELISA was 10~3 cfu/m L E.coli O157 in pure culture.Inoculation test of EHEC O157 in food samples indicated that the positive result could be detected when inoculated levels were 0.08 cfu/g with 8 h enrichment in negative beef or pork and 0.12 cfu/g( m L) with 10 h enrichment in negative vegetables and milk.