Molecular Methods for the Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 221

8.1. WHY MOLECULAR METHODS?
Water is a tasteless, odorless, colorless liquid that is an excellent solvent
and found in all organic tissues. Life as we know it would not exist without
water because it makes up approximately 75% of the volume of the human
body. Therefore, we require a continuous supply of potable water (i.e. water
that is safe to drink). Ensuring that water is chemically and biological free from
pollutants that can cause illness or disease requires knowledge about the poten-
tial contaminant as well as testing methods that are both specific and sensitive.
On the biological side, microbial water quality monitoring tests require the
detection and identification of the waterborne pathogens. Current culture-
dependent microbial analysis is not practical to routinely detect all the vari-
ous potential pathogens. Aside from the large number of possible pathogens
(bacteria, protozoa, viruses, etc.), many do not grow on laboratory media, do
not transport well from the water source to the laboratory, and require tests
that are expensive and time consuming. Therefore, traditionally, water quality
monitoring has been based on the presence or absence of indicator organisms
(organisms whose presence indicates fecal contamination and the potential
presence of pathogens but not necessarily the presence of a specific patho-
gen). 1 An ideal indicator organism would possess the following criteria 2,3 :
1. The organism should be present whenever enteric pathogens are present
and absent when the pathogens are absent.
2. The organism should be useful for all types of water.
3. The organism should have a life span similar to the pathogen.
4. The organism should not reproduce in water.
5. The organism should be harmless to humans.
6. Testing should have a high level of specificity and sensitivity.
7. Testing should be easy to perform and not too costly.
Coliforms and fecal coliforms have been recognized as good indicators of
fecal contamination and usually possess all the qualities of an ideal indicator.
Escherichia coli is the classic microbiological indicator; for the most part, it is
still the most commonly analyzed organism to evaluate the level of fecal con-
tamination. 1,4 Other indicator organisms that have been used include fecal
Enterococci , 5 Clostridium perfringens spores, 6 and somatic and male-specific coli-
phages. 5
Escherichia coli and other bacterial indicators have been found to have
good correlation with most bacterial pathogens; however, several studies