(pyocyanin synthesis by P. aeruginosa, production of the
antifungal pyrrolnitrin, and the alkyl-quinolone-like
compounds by B. cepacia) that could facilitate the colonization of various environments and enhance competitivity with
indigenous microbial populations (Norman et al. 2004).
Pathogens can also enter soil environments due to human
activities. Agricultural practices such as organic amendment
(cattle manure, pig slurry, sewage sludge), animal grazing,
or irrigation with microbiologically contaminated wastewater are potential sources of pathogens. The presence of
foodborne pathogens (Listeria monocytogenes, Salmonella
spp.), enteric bacteria, and opportunistic pathogens
(P. aeruginosa) in organic amendments has been reported
(Lavenir et al. 2007). The application of 1–2 t of sewage
sludge on French soils would led to the introduction of
10
6 –10
8 L. monocytogenes cells in soil per ha and per year
if wastes were not composted before land application
(Garrec et al. 2003). Numbers of 10
2 –10
5 cells of E. coli
O157:H7 per gram of bovine feces are mentioned. Transfer
of pathogens from contaminated soil to rivers through
leaching and runoff water has been shown (Ogden et al.
2001) such as transfer from contaminated irrigation water
to soil and crops (Solomon et al. 2002). In Australia, a study
from Vally et al. (2004) suggested that the water used to
irrigate a soccer field was the source of an outbreak due to
Aeromonas hydrophila among several soccer players.
Various studies aiming at evaluating the persistence of
introduced pathogens have reported long-term survival in
soil up to 1 year for Salmonella enterica, S. typhimurium,
and E. coli O157:H7 whether experiments were conducted at
the field (manure amendment) or the laboratory level
(inoculated soil microcosm) (You et al. 2006). On the opposite some studies revealed that E. coli O157:H7 was not
detectable 7 days (Ogden et al. 2001) or a few weeks
(Gagliardi and Karns 2002) after soil addition. Among the
various abiotic factors influencing pathogen survival temperature is the most frequently studied one. Data showed
E. coli O157:H7 survival being longer at high temperature
(15–21
C) than at low temperature (5
C) (Mukherjee et al.
2006). However, it has to be noticed that the impact of
temperature, pH, or clay content on pathogen survival
strongly varied from one pathogen to another (E. coli
O157:H7, Campylobacter, S. typhimurium, Yersinia
enterocolitica) (Guan and Holley 2003; Kidd et al. 2007).
Furthermore, several factors and their combined effects were
not yet investigated and should be taken into account to
better identify the environmental conditions favoring pathogen persistence, growth, and dispersal in soil.
Soils as any environment can also offer conditions
allowing a nonpathogenic bacterium to evolve toward a
pathogenic one. This is not yet investigated, but we must
be aware that new selective pressures occurred in various
ecosystems as a consequence of increasing worldwide population and intensive industrialization processes. Climate
change, intensive farming, and changes in agricultural
practices (see below paragraph on global change) introduce
new constraints on biota and impact ecological balances.
Microorganisms due to their short generation time can be
quickly affected by these changes. New genetic variants are
probably emerging within the microbial life, but we are not
yet able to predict their future impact on humans.
15.6 Sources of Pathogens Present in Aquatic
Environments
Even if some pathogens of concern (bacteria of the
genus Legionella, Pseudomonas aeruginosa, Aeromonas,
Burkholderia pseudomallei, and cyanobacteria) are natural
inhabitants of aquatic systems, most microbial waterborne
pathogens originate in the intestinal tract of humans and
animals and enter the aquatic environment via fecal contamination. This section devoted to the sources of waterborne
pathogens will be focused only on these enteric pathogens,
for which aquatic natural systems are not a primary
environment.
Among the sources of contamination, point sources are
usually distinguished from nonpoint (diffuse) sources. Major
point sources include discharges of raw urban wastewater,
domestic wastewater treatment plant (WWTP) effluents,
industrial wastewater effluents, and urban runoff waters
when they are collected by a separate sewer. In addition to
contribution from point sources, the natural environment also
receives fecal microorganisms by diffuse sources of contamination, which are more difficult to locate and quantify. No
clear definition of the term “diffuse sources” exists in the
literature. In this chapter, we consider it in its broadest
sense, i.e., including both diffuse contamination from animal
origin (wild animals and livestock) reaching the aquatic environment via runoff and soil leaching and diffuse contamination from human origin (leakage from sanitation systems such
as septic tanks, leaks in networks sanitation defaulters, etc.)
(Fig. 15.6). The relative importance of these various sources is
highly variable both in space and time; it depends of course on
the aquatic environment considered but also on hydrological
and meteorological conditions. If point sources from WWTPs
can be easily studied independently of other sources of contamination (and are also the subject of most studies on the
presence of enteric microorganisms in natural environments),
the flux of pathogenic microorganisms brought by nonpoint
sources, which can be dominant in rural watersheds, is much
more difficult to evaluate.
15.6.1 Point Sources
Domestic wastewater contains very high concentrations of
microorganisms of fecal origin. For example, E. coli
642
P. Lebaron et al.
antifungal pyrrolnitrin, and the alkyl-quinolone-like
compounds by B. cepacia) that could facilitate the colonization of various environments and enhance competitivity with
indigenous microbial populations (Norman et al. 2004).
Pathogens can also enter soil environments due to human
activities. Agricultural practices such as organic amendment
(cattle manure, pig slurry, sewage sludge), animal grazing,
or irrigation with microbiologically contaminated wastewater are potential sources of pathogens. The presence of
foodborne pathogens (Listeria monocytogenes, Salmonella
spp.), enteric bacteria, and opportunistic pathogens
(P. aeruginosa) in organic amendments has been reported
(Lavenir et al. 2007). The application of 1–2 t of sewage
sludge on French soils would led to the introduction of
10
6 –10
8 L. monocytogenes cells in soil per ha and per year
if wastes were not composted before land application
(Garrec et al. 2003). Numbers of 10
2 –10
5 cells of E. coli
O157:H7 per gram of bovine feces are mentioned. Transfer
of pathogens from contaminated soil to rivers through
leaching and runoff water has been shown (Ogden et al.
2001) such as transfer from contaminated irrigation water
to soil and crops (Solomon et al. 2002). In Australia, a study
from Vally et al. (2004) suggested that the water used to
irrigate a soccer field was the source of an outbreak due to
Aeromonas hydrophila among several soccer players.
Various studies aiming at evaluating the persistence of
introduced pathogens have reported long-term survival in
soil up to 1 year for Salmonella enterica, S. typhimurium,
and E. coli O157:H7 whether experiments were conducted at
the field (manure amendment) or the laboratory level
(inoculated soil microcosm) (You et al. 2006). On the opposite some studies revealed that E. coli O157:H7 was not
detectable 7 days (Ogden et al. 2001) or a few weeks
(Gagliardi and Karns 2002) after soil addition. Among the
various abiotic factors influencing pathogen survival temperature is the most frequently studied one. Data showed
E. coli O157:H7 survival being longer at high temperature
(15–21
C) than at low temperature (5
C) (Mukherjee et al.
2006). However, it has to be noticed that the impact of
temperature, pH, or clay content on pathogen survival
strongly varied from one pathogen to another (E. coli
O157:H7, Campylobacter, S. typhimurium, Yersinia
enterocolitica) (Guan and Holley 2003; Kidd et al. 2007).
Furthermore, several factors and their combined effects were
not yet investigated and should be taken into account to
better identify the environmental conditions favoring pathogen persistence, growth, and dispersal in soil.
Soils as any environment can also offer conditions
allowing a nonpathogenic bacterium to evolve toward a
pathogenic one. This is not yet investigated, but we must
be aware that new selective pressures occurred in various
ecosystems as a consequence of increasing worldwide population and intensive industrialization processes. Climate
change, intensive farming, and changes in agricultural
practices (see below paragraph on global change) introduce
new constraints on biota and impact ecological balances.
Microorganisms due to their short generation time can be
quickly affected by these changes. New genetic variants are
probably emerging within the microbial life, but we are not
yet able to predict their future impact on humans.
15.6 Sources of Pathogens Present in Aquatic
Environments
Even if some pathogens of concern (bacteria of the
genus Legionella, Pseudomonas aeruginosa, Aeromonas,
Burkholderia pseudomallei, and cyanobacteria) are natural
inhabitants of aquatic systems, most microbial waterborne
pathogens originate in the intestinal tract of humans and
animals and enter the aquatic environment via fecal contamination. This section devoted to the sources of waterborne
pathogens will be focused only on these enteric pathogens,
for which aquatic natural systems are not a primary
environment.
Among the sources of contamination, point sources are
usually distinguished from nonpoint (diffuse) sources. Major
point sources include discharges of raw urban wastewater,
domestic wastewater treatment plant (WWTP) effluents,
industrial wastewater effluents, and urban runoff waters
when they are collected by a separate sewer. In addition to
contribution from point sources, the natural environment also
receives fecal microorganisms by diffuse sources of contamination, which are more difficult to locate and quantify. No
clear definition of the term “diffuse sources” exists in the
literature. In this chapter, we consider it in its broadest
sense, i.e., including both diffuse contamination from animal
origin (wild animals and livestock) reaching the aquatic environment via runoff and soil leaching and diffuse contamination from human origin (leakage from sanitation systems such
as septic tanks, leaks in networks sanitation defaulters, etc.)
(Fig. 15.6). The relative importance of these various sources is
highly variable both in space and time; it depends of course on
the aquatic environment considered but also on hydrological
and meteorological conditions. If point sources from WWTPs
can be easily studied independently of other sources of contamination (and are also the subject of most studies on the
presence of enteric microorganisms in natural environments),
the flux of pathogenic microorganisms brought by nonpoint
sources, which can be dominant in rural watersheds, is much
more difficult to evaluate.
15.6.1 Point Sources
Domestic wastewater contains very high concentrations of
microorganisms of fecal origin. For example, E. coli
642
P. Lebaron et al.