Agriculture Reference
In-Depth Information
in water. Below 8 °C enteric viruses are capable of surviving for months in aquatic
environments (Kutz and Gerba 1988 ).
Survival of
E. coli
O157:H7 in surface waters was found to be greater at lower
temperatures (Czajkowska and others 2005) and was two to three times greater in river
and lake sediments at the same temperatures. In water contaminated with manure,
E.
coli
O157:H7 was observed to survive at outside ambient temperatures for 92 days
(McGee and others 2002).
Enteric bacteria and viruses will also survive for longer periods of time in aquatic
sediments than in the overlaying water probably because of the increased presence of
organics and the thermostabilization of viruses (Karim and others 2004; Liew and
Gerba 1980; Hendricks 1971a). Karim and others (2004) found that the die-off of
Giardia
cysts was greater in sediments from a pond use to treated secondary sewage
effl uents.
Water Testing
The routine examination of water for the presence of enteric pathogens is often a
tedious, diffi cult, costly, and time-consuming task. Thus, indicator organisms have
been used to assess the presence of fecal contamination and the effectiveness of
sewage treatment processes. Developed at the turn of the last century for assessing
fecal contamination, the indicator concept depends on the fact that certain nonpatho-
genic bacteria occur in the feces of all warm-blooded animals. These bacteria can
easily be isolated and quantifi ed by simple methods. Detection of these bacteria in
water means that fecal contamination has occurred and suggests that enteric pathogens
may also be present. For example, coliform bacteria, which normally occur in the
intestines of all warm-blooded animals, are excreted in great numbers in feces. In
polluted water, coliform bacteria are found in densities roughly proportional to the
degree of fecal pollution. Because coliform bacteria are generally hardier than disease-
causing bacteria, their absence from water is an indication that the water is bacterio-
logically safe for human consumption.
Indicators have traditionally been used to suggest the presence of enteric pathogens;
however, today we recognize that there is rarely a direct correlation between bacterial
indicators and human pathogens (Ashbolt and others 2001). As such, the use of indica-
tors is better defi ned by their intended purpose (Table 7.2). Thus, process indicators
Table 7.2.
Defi nitions and examples of indicator microorganisms
Group
Defi nition and Examples
Process indicator
A group of organisms that demonstrate the effi cacy of a process, such as
total heterotrophic bacteria or total coliforms for chlorine disinfection
Fecal indicator
A group of organisms that indicate the presence of fecal contamination,
such as the fecal coliforms or
Escherichia coli
Index and model
organisms
A group or species indicative of pathogen presence and behavior,
respectively, such as
E. coli
as an index for Salmonella and male-specifi c
coliphages as models for human enteric viruses
Modifi ed from Ashbolt and others (2001).
