Discussion by Ralph Mitchell
The introduction of membrane filtration techniques and highly specific culture media have made
the detection of fecal bacteria and particularly fecal streptococci relatively simpler and more rapid.
They have the added advantage for routine laboratories of not requiring either highly complex
materials or skilled staff. However, there is a major disadvantage in the use of cultural methods. Quite
frequently the indicator bacteria are physiologically atypical. The work described in the paper under
discussion provides an excellent example of the unreliability of cultural techniques. By comparison the
fluorescent antibody technique has been shown to be highly specific for fecal streptococci.
The fluorescent antibody technique offers the greatest promise when it is considered in the context
of continuous monitoring. Samples of water could be rapidly assayed at regular intervals for fecal
contamination by mixing with fluorescent antibody in an automated system. The presence of fecal
streptococci would be detected by the formation of fluorescent pigments in positive samples. Pavlova
and her co-workers make use of the intensity of fluorescence to determine specificity of reaction. This
type of reaction has been used to an increasing extent as a diagnostic tool for pathogens in recent
years. It has gained acceptance because of the high degree of specificity and the rapidity of the test. A
potential drawback to its routine use is the requirement for a continuous supply pf specific antibody.
Use of the technique for fecal contamination of water samples would require regular distribution of
antibody to the testing laboratories. Individual preparation of serum would be technically difficult and
uneconomical.
The use of streptococci to indicate the presence of fecal contamination of water is fraught with
many pitfalls. It is important that the indicator organism have a die-away curve which is typical of the
common human pathogens in sewage. Streptococcus fecalis has a much higher degree of resistance in
natural waters than many other fecal bacteria. The rate of predation in native microorganisms on fecal
streptococci in natural waters would not be expected to parallel the rate of predation on most fecal
bacteria. Thus, one might be led to the false conclusion by a positive test for fecal streptococci that
fecal contamination had occurred recently, when in fact contamination had occurred some time ago
and the majority of fecal organisms had disappeared.
Another possible pitfall in the use of fecal streptococci as an indicator of fecal contamination is the
presence of bacteria belonging to this group on uncontaminated crops. Waters containing wastes from
food processing industries frequently yield false positive tests for fecal streptococci.
The presence of Escherichia coli in natural waters is a highly reliable test for recent fecal
contamination. This organism is present in huge numbers in human feces and its rate of decline in
natural waters mirrors that of important water-borne human pathogens, such as Salmonella typhosa.
The conventional tests for fecal coliforms are no less cumbersome than those for fecal streptococci. It
would be a significant advance if Pavlova and her co-workers could use their technique to specifically
detect low concentrations of E. coli in the presence of mixed bacterial populations in natural waters.
We are moving away from the classical methods of identification of microorganisms by cultivation
on a variety of media. Modern techniques of chemical analysis enable us to determine qualitatively and
quantitatively extremely low concentrations of chemicals. It is now possible to obtain the
"fingerprint" of a bacterium by passing the growth medium through a gas-chromatograph which shows
the characteristic spectrum of metabolites produced by that organism. Even a few cells of E. coli can
be detected in this way and water can be monitored continuously for fecal contamination. The use of
this modern method and the fluorescent antibody technique described by Pavlova and her co-workers
point to the development of more sensitive and rapid methods of detecting fecal contamination of
natural waters. It is hoped that this approach will lead to the eventual development of a continuous
automatic monitoring process which will make use of a single chemical test for fecal contamination
which will be both sensitive and representative.
H. Leclerc, France
The technique of Shattuck of enzymic extraction is better than the defective technique of
Lancefield for streptococci. The authors' technique is of interest because it differs from the methods
used for secondard human or animal faecal organisms and such very simple methods as Mead's using
tyrosine discarboxylic acid and fermentation with sorbitol. The fluorescence method improves
identification but is more costly and complicated. It is not essential, however, for the identification of
streptococcus D.
T J. Stamps, Rhodesia.
Certain pathogens such as poliovirus and S. typhosa can outlast E. coli especially in oxidation
ponds. Is it not therefore better to utilise more persistent organisms such as Str. faecalis as sewage
contaminant indicators?
71
The introduction of membrane filtration techniques and highly specific culture media have made
the detection of fecal bacteria and particularly fecal streptococci relatively simpler and more rapid.
They have the added advantage for routine laboratories of not requiring either highly complex
materials or skilled staff. However, there is a major disadvantage in the use of cultural methods. Quite
frequently the indicator bacteria are physiologically atypical. The work described in the paper under
discussion provides an excellent example of the unreliability of cultural techniques. By comparison the
fluorescent antibody technique has been shown to be highly specific for fecal streptococci.
The fluorescent antibody technique offers the greatest promise when it is considered in the context
of continuous monitoring. Samples of water could be rapidly assayed at regular intervals for fecal
contamination by mixing with fluorescent antibody in an automated system. The presence of fecal
streptococci would be detected by the formation of fluorescent pigments in positive samples. Pavlova
and her co-workers make use of the intensity of fluorescence to determine specificity of reaction. This
type of reaction has been used to an increasing extent as a diagnostic tool for pathogens in recent
years. It has gained acceptance because of the high degree of specificity and the rapidity of the test. A
potential drawback to its routine use is the requirement for a continuous supply pf specific antibody.
Use of the technique for fecal contamination of water samples would require regular distribution of
antibody to the testing laboratories. Individual preparation of serum would be technically difficult and
uneconomical.
The use of streptococci to indicate the presence of fecal contamination of water is fraught with
many pitfalls. It is important that the indicator organism have a die-away curve which is typical of the
common human pathogens in sewage. Streptococcus fecalis has a much higher degree of resistance in
natural waters than many other fecal bacteria. The rate of predation in native microorganisms on fecal
streptococci in natural waters would not be expected to parallel the rate of predation on most fecal
bacteria. Thus, one might be led to the false conclusion by a positive test for fecal streptococci that
fecal contamination had occurred recently, when in fact contamination had occurred some time ago
and the majority of fecal organisms had disappeared.
Another possible pitfall in the use of fecal streptococci as an indicator of fecal contamination is the
presence of bacteria belonging to this group on uncontaminated crops. Waters containing wastes from
food processing industries frequently yield false positive tests for fecal streptococci.
The presence of Escherichia coli in natural waters is a highly reliable test for recent fecal
contamination. This organism is present in huge numbers in human feces and its rate of decline in
natural waters mirrors that of important water-borne human pathogens, such as Salmonella typhosa.
The conventional tests for fecal coliforms are no less cumbersome than those for fecal streptococci. It
would be a significant advance if Pavlova and her co-workers could use their technique to specifically
detect low concentrations of E. coli in the presence of mixed bacterial populations in natural waters.
We are moving away from the classical methods of identification of microorganisms by cultivation
on a variety of media. Modern techniques of chemical analysis enable us to determine qualitatively and
quantitatively extremely low concentrations of chemicals. It is now possible to obtain the
"fingerprint" of a bacterium by passing the growth medium through a gas-chromatograph which shows
the characteristic spectrum of metabolites produced by that organism. Even a few cells of E. coli can
be detected in this way and water can be monitored continuously for fecal contamination. The use of
this modern method and the fluorescent antibody technique described by Pavlova and her co-workers
point to the development of more sensitive and rapid methods of detecting fecal contamination of
natural waters. It is hoped that this approach will lead to the eventual development of a continuous
automatic monitoring process which will make use of a single chemical test for fecal contamination
which will be both sensitive and representative.
H. Leclerc, France
The technique of Shattuck of enzymic extraction is better than the defective technique of
Lancefield for streptococci. The authors' technique is of interest because it differs from the methods
used for secondard human or animal faecal organisms and such very simple methods as Mead's using
tyrosine discarboxylic acid and fermentation with sorbitol. The fluorescence method improves
identification but is more costly and complicated. It is not essential, however, for the identification of
streptococcus D.
T J. Stamps, Rhodesia.
Certain pathogens such as poliovirus and S. typhosa can outlast E. coli especially in oxidation
ponds. Is it not therefore better to utilise more persistent organisms such as Str. faecalis as sewage
contaminant indicators?
71