must be confirmed (Phebus and Fung, 1994).
These beads have been used to detect E. coli
O157:H7 in foods.
A latex agglutination test can provide quick
results with an acceptable degree of specificity
for E. coliO157 but not for H7 confirmation.
An available assay uses a polyclonal O157
antibody coated onto polystyrene latex par-
ticles, and a slide agglutination format is
incorporated to transfer a suspect culture to a
paper card, followed by the addition of the
antibody reagent. The presence of the O157
antigen is indicated by agglutination.
A lateral flow immunoprecipitate assay
has been developed recently as a screen test
for E. coliO157:H7. This assay, approved by
the Association of Official Analytical
Chemists (AOAC), requires an enrichment
broth and incubation for 20 hours at 36ºC. A
0.1 mL sample of the enrichment broth is
then deposited in a test window in a self-con-
tained, single-use test device that contains
proprietary reagents. As lateral flow occurs
across the reagent zone, the target antigen, if
present, reacts with the reagents to form an
antigen–antibody–chromgen complex. After
approximately 10 minutes of incubation at
room temperature, a line will form in the test
window, indicating the possible presence of
E. coliO157:H7. If no line appears, a con-
firmed negative test results. As flow contin-
ues through the test verification zone, all
samples will react with reagents, and a line
will appear, indicating proper completion of
the test. A positive test does not ensure that
anE. coliO157:H7 strain exists. The suspect
sample must be further tested to confirm the
presence of the pathogen. This test, which is
easy to conduct, incorporates an assay sys-
tem into a single test unit (Anon., 1998).
Spiral Assay System
This equipment deposits a liquid sample in
a spiral pattern onto a rotating agar plate and
can create a 3 log dilution effect. The merits
of this system include reduced or elimination
of serial dilutions, less materials (pipettes,
plates, media, and other supplies), less time
and labor, and simplified plate counting. The
disadvantages of this system include invest-
ment cost and required specialized equipment
(i.e., plating machine and counting machine).RapID ONE System
This test for Enterobacteriaceaerelies on
preformed enzymes. It is a one-step inocula-
tion that is easy to use. Results are obtained
in 4 hours, but a competent microbiologist is
required for correct interpretation.Crystal™ Identification Systems
This system relies on preformed enzymes.
It is a one-step inoculation that is easy to use
with the inoculum being suspended in lysing
buffer. Results may be obtained in 3 hours
with a computer assisted ID match; however,
a competent technician is required for con-
sistent interpretation.Salmonella1-2 Test
This rapid screening test for Salmonellais
conducted in a single-use, plastic device that
contains a nonselective motility medium and
a selective enrichment broth. A positive test
is indicated by an immobilization precipita-
tion band that forms in the motility medium
from the reaction of motile Salmonellawith
flagellar antibodies.
This test uses a clear plastic device with
two chambers. The smaller chamber con-
tains a peptone-based, nonselective motil-
ity medium. The sample is added to the
tetrathionate-brilliant green-serine broth
contained in the inoculation chamber of the
1-2 test unit. After approximately 4 hours of
incubation, motile Salmonellaemove from
the selective motility medium. As these
organisms progress through the motility
medium, they encounter flagellar antibodies
that have been diffused into this medium.The Relationship of Microorganisms to Sanitation 63