Biology Reference
In-Depth Information
have shown that both E. coli and Enterococci are not well correlated with
Salmonella or Campylobacter . 3 Recent studies have also questioned the
suitability of bacterial indicators for viral or protozoan pathogens. 4,7-10
Therefore, all presently used indicators fall short on one or more of
the criteria as an ideal indicator organism. Furthermore, culture-based
methods can be lengthy to perform, labor intensive, and unable to detect
unculturable species. 11 Their limitations have sparked a renewed quest to
develop alternative methods to ensure absolute safety of drinking water.
The development and use of molecular methods have recently shown
great promise as fast, sensitive, specific, and quantitative ways to detect
waterborne pathogens.
8.1.1. Waterborne pathogens
Waterborne pathogens fall into several groups of organisms including bacte-
ria, cyanobacteria, protozoa, viruses, and helminths. Although helminths are
an interesting pathogenic group of parasites, this chapter will concentrate
on the microbial pathogens included in the other four groups.
Currently there is no universal method to collect, detect, and identify
all pathogenic microbes from a water sample. Along with the use of indica-
tor organisms that may or may not correlate well with pathogen levels, the
collection of the sample can also influence the ability to detect the pathogen.
For example, detection of some viral pathogens from drinking water may
require a concentration of up to 1000 L. 12 In the case of protozoan detection,
operator skill is paramount because detection relies on manual scanning of
concentrated samples on microscopic slides and the identification of suspect
objects, such as cysts and oocysts, using further specialized microscopy. 13
Molecular methods can provide sensitive, rapid, and quantitative analyti-
cal tools for detecting specific pathogens, including emergent strains and
indicators. They have been used to evaluate food and water, both raw and
treated/processed. The advantages of molecular methods are many. First,
they circumvent the need to culture the pathogens, a procedure that is
not efficient for some organisms. They can be very specific for particular
species and provide further phylogenetic information about the strains. In
some cases, strains can be used to track the identification of the source of
the contamination in the water source. 3,14 Due to an amplification step
in most molecular methods, very minute amounts of pathogens can be
detected. Lastly, many molecular methods lend themselves to the possibility
of automation, which can lead to real-time analysis and provide information
for microbial risk assessment purposes. 4
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