Pa. Chapman et al., USE OF COMMERCIAL ENZYME IMMUNOASSAYS AND IMMUNOMAGNETIC SEPARATION SYSTEMS FOR DETECTING ESCHERICHIA-COLI O157 IN BOVINE FECAL SAMPLES, Applied and environmental microbiology, 63(7), 1997, pp. 2549-2553
A commercial enzyme immunoassay (EIA) (E. coli O157 Visual Immunoassay
; Tecra Diagnostics) performed on enrichment cultures in modified Esch
erichia coli broth (mECn) was compared with immunomagnetic separation
(IMS) (Dynabeads anti-E. coli O157; Dynal) performed on enrichment cul
tures in modified buffered peptone water (BPW-VCC) for the detection o
f E. coli O157 in bovine fecal samples. Tests on fecal suspensions ino
culated with each of 12 different strains of E. coli O157 showed that
both the EIA and IMS methods were 10- to 100-fold more sensitive than
direct culture or enrichment subculture methods for detection of the o
rganism, EIA and IMS were then compared for detection of E. coli O157
in bovine rectal swabs. For confirmation of positive ELA tests, a comm
ercial system (Immunocapture System [ICS]; Tecra Diagnostics) was comp
ared with IMS; both were performed on mECn enrichment cultures. Of 200
rectal swabs examined, 17 gave positive results in the EIA which were
confirmed by both confirmation systems, 2 gave positive results in th
e EIA which were confirmed by IMS but not by ICS, and 1 gave a positiv
e result in the EIA which was confirmed by ICS but not by IMS. Of thes
e 20, 15 were also positive by the BPW-VCC-IMS culture system; a furth
er 3 samples were positive by this culture system but gave a negative
result in the EIA. Eight samples were negative by the BPW-VCC-IMS cult
ure system but gave a positive result in the EU which could not be con
firmed by either confirmation system. Further examination of the eight
unconfirmed EIA-positive samples yielded sorbitol-fermenting E. coli
O157 from three samples, Of the remaining five cultures, four were pos
itive in an EIA for verocytotoxins (VT) and two were positive in a cel
l culture assay for VT,. The remaining 170 samples were negative by bo
th EW and BPW-VCC-IMS. The Tecra EIA and IMS are both technically simp
le and sensitive methods for detecting E. coli O157 in bovine fetal sa
mples. There was no statistically significant difference between the n
umbers of positives detected by the different assays (P = 0.29).