Bacteriophages as Indicators for Enteric Viruses and Public Health
Risks in Groundwaters
THE ISSUE
For more than 100 years, there has been debate among microbiologists
and
public health practitioners concerning the role of drinking water
monitoring
for either pathogens or indicators. By the 1890s, it was generally
accepted that
monitoring for specific pathogens was not in the best interest of
public health
protection because there were too many pathogens, they were present
in very
small concentrations, and methods for their detection were not practical.
Public health officials decided that monitoring would be conducted
to detect
fecal pollution and not for individual pathogens.
Escherichia coli became the primary indicator of fecal pollution
at the time.
Because methods for the specific detection and identification of
E. coli were
not well developed, an E. coli surrogate - the total coliform group
- was devel-
oped. Its detection was based on the physiological observation
that the fer-
mentation of lactose in a growth medium that allowed the manifestation
of
only enteric bacteria would elucidate E. coli and its relatives,
the total col-
iforms. Shortly thereafter, coliform monitoring became codified
throughout
the world. Coliform monitoring, being rapid, inexpensive, and easy
to perform,
proved effective. There are low rates of waterborne bacterial disease
outbreaks
in developed countries today.
Beginning in the 1970s, the role of drinking water transmission
of enteric
viruses became a subject for concerted studies. It was found
that coliforms
might differ biologically from the fate of animal viruses in
drinking water.
RESEARCH STRATEGY
Practicing microbiologists in Europe and the United States (Dr.
Henri LeClerc,
Institut Pasteur de Lille; Dr. Steve Edberg, Yale University; Jean
Marie Delattre,
Faculte de medecine de Lille) collaborated to write a peer-reviewed
paper that
frames the issues regarding the use of bacteriophages as indicators
of fecal
pollution. The review summarizes the basic strengths and weaknesses
of bac-
teriophages as indicators and clearly frames the questions that need
to be
answered before bacteriophages can be accepted in the regulatory
framework.
MAJOR FINDINGS AND SIGNIFICANCE
Overall, the conclusion with regard to monitoring for enteric viruses
is much
the same as that decided by public health officials in the 1890's.
To protect the
public's health, it is better to monitor for the indicators of fecal
pollution
rather than for specific pathogens. The overriding rationale for
this conclusion
is that there are still unknown (and simply too many) enteric viral
pathogens.
Moreover, they are present in low concentrations, often requiring
the analyst
to examine more than 10 liters of water. Although methods have
been pro-
posed for many of the enteric viruses, they are generally quite
expensive, tech-
nically demanding, and time consuming. From distribution water,
where the
strategy is to detect relatively recent fecal contamination events,
E. coli and
total coliforms are the most useful because they can be monitored
frequently
and inexpensively with easy-to-do, specific tests.
For groundwater, while this strategy has proven effective, the
situation is com-
pounded. Here, the infectious particle must travel throughout the
aquifer or
subterranean water source. Because viruses are smaller than bacteria,
there has
been concern that the transit times of the bacterial indicators
may not be
equivalent to those of the human enteric viruses. Moreover, there
has been
some work indicating that some viral pathogens may be differently
resistant
to environmental conditions, sewage or water treatment processes,
compared
to coliform organisms. There are circumstances in which viruses
may survive
in the water environment when indicator fecal bacteria do not.
Accordingly,
with recent developments in the ability to detect enteric viral
pathogens and
viral surrogates, it is appropriate to consider how best to monitor
for enteric
viruses in groundwater.
This scientific review considers both direct detection methods,
and primarily,
the proposed viral surrogate and fecal indicators, the bacteriophage.
The
review found that low concentrations of all types of bacteriophages
in ground-
water limit their power to predict the presence of enteric viruses.
There is lit-
tle concordance in the literature regarding phage detection methods,
thus
making comparisons extremely difficult. Different authors have
used different
hosts, phage concentration methods, and end-point determinations.
Also,
markedly different volumes of sample have been employed, varying
from 1
liter to 400 liters. In addition, bacteriophage concentration methods
are not
reproducible. Moreover, there is no consensus on the best bacterial
host strain,
and there is a lack of consistent recovery of bacteriophages from
individual
fecal specimens. While bacteriophages may be appealing as indicators
of
groundwater enteric virus pollution, their use is premature at
this time and a
number of critical issues must be addressed in order for them to
meet mini-
mum regulatory requirements.
LeClerc, H., Edberg, S.C., Pierzo, V. and Delattre, J.M., Bacteriophages
as Indicators of Enteric
Viruses and Public Health Risk in Groundwaters, Journal of Applied
Microbiology 88(1).
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