This fecal indicator paradigm developed at the end of the nineteenth century,
because it was obvious that waterborne diseases were mostly gastroenteritis. Since it
was impossible to monitor all enteric pathogens, microbiologists focused on FIBs as
indirect predictors of their presence ([10–12]). In 1892, Schardinger [12] proposed
using Bacterium coli which was isolated by Theodor Escherich in 1885 [13] and was
renamed Escherichia coli in 1919 [14]. Selective media were later developed for the
quantification of E. coli in drinking waters, surface waters, and wastewaters.
Thermotolerant coliforms (also called fecal coliforms) that include E. coli were
used for a while as indicators; however, their lack of specificity resulted in their
being dropped in the revised Bathing Water Directive in 2006. Enterococci were
integrated into the monitoring of FIBs when Slanetz et al. [15] proposed a selective
medium for their detection; they were first named fecal streptococci [14].
Although the FIB concept proved to be useful for several decades to estimate
potential health risk and contributed greatly to decreasing the occurrence of waterborne diseases in industrialized countries, it has many drawbacks. Some FIB strains
survive and even grow in sand, sediment, soil, and waterbodies, which may serve as
potential reservoirs [16–18]. Culture-based assays cannot distinguish whether the
source of contamination is animal or human [19]. The correlation between coliforms
and human pathogens has not been validated over a wide range of waterbodies with
differences in water quality, geographic origin, climatic conditions, watershed
morphology and hydrology, and local pollution inputs. In fact, the FIB/pathogen
ratio in natural waters is mainly a function of the occurrence of pathogens in the
population, different fates in water treatments, and different survival times in the
environment. These ratios are therefore site-specific and seasonally dependent and
show substantial spatial and temporal variations [20–22].
As a consequence, there is often no correlation between FIB and pathogen
concentrations, which prevent efficient prediction of contamination [23–25]. In the
Seine River in the Paris area, virus monitoring carried out in 2013–2014 and
2017–2018 showed no significant correlation between FIBs and a panel of various
enteric viruses (Fig. 4). From January 2005 to August 2007, only a significant
correlation could be found between IE and Giardia cysts in the Seine and Marne
rivers [26]; other fecal bacteria were not correlated with the protozoans monitored.
To counter some of these drawbacks, new indicators were developed using
molecular techniques. Microbial source tracking methods distinguish human and
animal sources using genetic markers such as specific gut bacteria or comparison of
bacterial communities [9, 27]. Bacteroidetes or Firmicutes species and fecal bacteriophages were identified as potential alternate indicators [19, 28]. Although somatic
coliphage and F-specific RNA phage are sometimes used by stakeholders, these
indicators are still not implemented in the EU Bathing Directive, and E. coli and IE
remain the gold standard [29].
In conclusion, the presence of FIBs can predict the probable presence of viruses,
Giardia, and Cryptosporidium in surface water affected by sewage inputs, but they
cannot predict their concentration. This is in accordance with the original indicator
concept in drinking water, which established FIBs as an index of fecal pollution and,
therefore, the probability of the presence of pathogens and potential health risks.
330
J.-M. Mouchel et al.
because it was obvious that waterborne diseases were mostly gastroenteritis. Since it
was impossible to monitor all enteric pathogens, microbiologists focused on FIBs as
indirect predictors of their presence ([10–12]). In 1892, Schardinger [12] proposed
using Bacterium coli which was isolated by Theodor Escherich in 1885 [13] and was
renamed Escherichia coli in 1919 [14]. Selective media were later developed for the
quantification of E. coli in drinking waters, surface waters, and wastewaters.
Thermotolerant coliforms (also called fecal coliforms) that include E. coli were
used for a while as indicators; however, their lack of specificity resulted in their
being dropped in the revised Bathing Water Directive in 2006. Enterococci were
integrated into the monitoring of FIBs when Slanetz et al. [15] proposed a selective
medium for their detection; they were first named fecal streptococci [14].
Although the FIB concept proved to be useful for several decades to estimate
potential health risk and contributed greatly to decreasing the occurrence of waterborne diseases in industrialized countries, it has many drawbacks. Some FIB strains
survive and even grow in sand, sediment, soil, and waterbodies, which may serve as
potential reservoirs [16–18]. Culture-based assays cannot distinguish whether the
source of contamination is animal or human [19]. The correlation between coliforms
and human pathogens has not been validated over a wide range of waterbodies with
differences in water quality, geographic origin, climatic conditions, watershed
morphology and hydrology, and local pollution inputs. In fact, the FIB/pathogen
ratio in natural waters is mainly a function of the occurrence of pathogens in the
population, different fates in water treatments, and different survival times in the
environment. These ratios are therefore site-specific and seasonally dependent and
show substantial spatial and temporal variations [20–22].
As a consequence, there is often no correlation between FIB and pathogen
concentrations, which prevent efficient prediction of contamination [23–25]. In the
Seine River in the Paris area, virus monitoring carried out in 2013–2014 and
2017–2018 showed no significant correlation between FIBs and a panel of various
enteric viruses (Fig. 4). From January 2005 to August 2007, only a significant
correlation could be found between IE and Giardia cysts in the Seine and Marne
rivers [26]; other fecal bacteria were not correlated with the protozoans monitored.
To counter some of these drawbacks, new indicators were developed using
molecular techniques. Microbial source tracking methods distinguish human and
animal sources using genetic markers such as specific gut bacteria or comparison of
bacterial communities [9, 27]. Bacteroidetes or Firmicutes species and fecal bacteriophages were identified as potential alternate indicators [19, 28]. Although somatic
coliphage and F-specific RNA phage are sometimes used by stakeholders, these
indicators are still not implemented in the EU Bathing Directive, and E. coli and IE
remain the gold standard [29].
In conclusion, the presence of FIBs can predict the probable presence of viruses,
Giardia, and Cryptosporidium in surface water affected by sewage inputs, but they
cannot predict their concentration. This is in accordance with the original indicator
concept in drinking water, which established FIBs as an index of fecal pollution and,
therefore, the probability of the presence of pathogens and potential health risks.
330
J.-M. Mouchel et al.