Molecular Methods for the Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 228

for Leuconostoc and Fructobacillus , respectively. 25 The amount of the sample
that could be analyzed was found to be critical. The extra time required
to prepare a suitable sample must be considered when using this method
as a standard for testing environmental samples when protein concentra-
tions are not known beforehand.
Current research has demonstrated that the fabrication of titanium bac-
terial chips could be used as bacterial sensors by immersing the plates in the
solution to capture bacterial cells from the sample. The chips then could be
used directly to analyze the captured cells via MALDI-MS. 26 The lowest
detectable concentration of bacterial cells was 1 × 10 4 cfu mL −1 . The device
has yet to be tried on environmental samples for the ability to capture
bacterial cells.
8.2.2.2. Immunological techniques
Antibody-based techniques have also been investigated for their ability to
detect bacteria in environmental samples. 27 The development of several
immunological methods for the detection and enumeration of pathogenic
organisms in water sources has become a more recent focus. Most of these
studies have targeted either the O or H antigens of E. coli O157. Albeit the
limitation that E. coli O157 may lose its O antigenicity under starvation
conditions and still retain its ability to produce toxin causing false nega-
tives, 40 many studies have shown successful immunological detection of the
pathogen from water samples.
8.2.2.3. Enzyme-linked immunosorbant assay
Enzyme-linked immunosorbant assay (ELISA) can be used to detect and
measure either antibodies or antigens. The most widely used versions of
ELISA for the detection of bacterial cells in suspensions (water, etc.) are
competitive ELISA and sandwich ELISA ( Fig. 8.3 ). 28 In the latter case,
a specific antibody is bound to the bottom of microtiter plates and then
the sample is added to the wells. If the target antigen is present, it will
bind to the antibody and can be detected with a conjugate. A conjugate
is another antibody attached to an enzyme that converts a supplied sub-
strate to a colormetric, fluorescent, or chemiluminescent product that
can be detected.
Park et al. 29,30 has shown that a sandwich ELISA assay could be used
to detect E. coli O157:H7 and Salmonella typhimurium . They were able to
detect 1.8 × 10 3 cfu mL −1 of E. coli within 30 min and 9.2 × 10 3 cfu mL −1 of
Salmonella within 20 min.