84
Discussion
E.L. Shanas, Israel.
E.coli and faecal streptococcus are poor indicators of faecal pollution in chlorinated supplies.
Identifying E.coli phages which are probably more resistant to chlorine as are viruses might prove to
be a more reliable test in chlorinated supplies.
Reply
Mr. Shanas is right. E. coliphages are more resistant than coliform bacteria; we are performing
currently a study in which we try to prove that E. coliphages could be used as viral indicator in water
and wastewater. The results so far achieved are encouraging.
M. Gould, USA.
With regard to the finding of occasional E.coli in chlorinated samples it is important to distinguish
between free residual chlorine and combined chlorine residuals. We have never isolated E.coli or other
coliforms from water containing free residual chlorine but we have isolated E.coli on rare occasions
and other coliforms more frequently from samples containing combined or chloramine residuals.
Reply
The remark is correct; however in practice we find few E. coli and other coliform in 1000 ml which
were not detected in 100 ml samples. This was found to be important especially when chlorinated
water was recharged to wells and the coliforms that survived after chlorination multiplied in the
underground.
Reply to Prof. Leclerc
1) All the strains of E. coli used as hosts for specific bacteriophages have been identified first by
biochemical tests. Mainly by the IMViC test, by their reaction on EMB medium and growth
in Boric acid medium at 43°C. Three hundred various E. coli strains have been tested for
that purpose, furthermore, in order to ascertain that the reaction on MmFc medium is
compatible with the biochemical ones, 200 various E.coli and A. aerogenes strains have been
tested. The E.coli strains developed into dark blue colonies and the A.aerogenes into light pink
colonies. All the E.coli bacteriophages used in the test were isolated on these E.coli bacteria.
Being aware of the possibility of crossreaction with other Enterobacteriaceae, all the E.coli
bacteriphages isolated, have been tested for their host specificity to E.coli strains, and their
behaviour with various Salmonella as well as A.aerogenes strains of bacteria. Chosen for the test
were those bacteriophages with high specificity for E.coli bacteria. In addition parallel
determinations have been performed using the bacteriophage test and the elevated temperature
test (incubation at 44.5°C Geldreich). Among the hundreds of comparative tests performed
there was a good correlation, the number of positive results being in favour of the
bacteriophage test.
2) As to the second remark. We showed and stressed the fact that the test has been devised for
establishing bacteriological water quality, hence low contamination. Within these constraints
the test is very satisfactory and the results obtained are accurate. As pollution grows, of course,
the picture on the filter is less clear and therefore dilutions are advisable - But this is the
drawback of the filtration method in general.
Discussion
E.L. Shanas, Israel.
E.coli and faecal streptococcus are poor indicators of faecal pollution in chlorinated supplies.
Identifying E.coli phages which are probably more resistant to chlorine as are viruses might prove to
be a more reliable test in chlorinated supplies.
Reply
Mr. Shanas is right. E. coliphages are more resistant than coliform bacteria; we are performing
currently a study in which we try to prove that E. coliphages could be used as viral indicator in water
and wastewater. The results so far achieved are encouraging.
M. Gould, USA.
With regard to the finding of occasional E.coli in chlorinated samples it is important to distinguish
between free residual chlorine and combined chlorine residuals. We have never isolated E.coli or other
coliforms from water containing free residual chlorine but we have isolated E.coli on rare occasions
and other coliforms more frequently from samples containing combined or chloramine residuals.
Reply
The remark is correct; however in practice we find few E. coli and other coliform in 1000 ml which
were not detected in 100 ml samples. This was found to be important especially when chlorinated
water was recharged to wells and the coliforms that survived after chlorination multiplied in the
underground.
Reply to Prof. Leclerc
1) All the strains of E. coli used as hosts for specific bacteriophages have been identified first by
biochemical tests. Mainly by the IMViC test, by their reaction on EMB medium and growth
in Boric acid medium at 43°C. Three hundred various E. coli strains have been tested for
that purpose, furthermore, in order to ascertain that the reaction on MmFc medium is
compatible with the biochemical ones, 200 various E.coli and A. aerogenes strains have been
tested. The E.coli strains developed into dark blue colonies and the A.aerogenes into light pink
colonies. All the E.coli bacteriophages used in the test were isolated on these E.coli bacteria.
Being aware of the possibility of crossreaction with other Enterobacteriaceae, all the E.coli
bacteriphages isolated, have been tested for their host specificity to E.coli strains, and their
behaviour with various Salmonella as well as A.aerogenes strains of bacteria. Chosen for the test
were those bacteriophages with high specificity for E.coli bacteria. In addition parallel
determinations have been performed using the bacteriophage test and the elevated temperature
test (incubation at 44.5°C Geldreich). Among the hundreds of comparative tests performed
there was a good correlation, the number of positive results being in favour of the
bacteriophage test.
2) As to the second remark. We showed and stressed the fact that the test has been devised for
establishing bacteriological water quality, hence low contamination. Within these constraints
the test is very satisfactory and the results obtained are accurate. As pollution grows, of course,
the picture on the filter is less clear and therefore dilutions are advisable - But this is the
drawback of the filtration method in general.