A NEW APPROACH IN E.coli IDENTIFICATION
N. BURAS and Y. KOTT
Environmental Engineering Laboratories, Technion,
Israel Institute of Technology, Haifa, Israel
INTRODUCTION
Although serious efforts are directed into developing ways and media for the isolation
and quantification of pathogens in water (Livingstone, 1965; McCoy, 1968; Moore,
1951), the most accepted method for the determination of the bacteriological water
quality is still the quantitative evaluation of the coliform group of bacteria as a whole
(Standard Methods, 1965).
Lately a number of new methods have been described (Perry et al, 1944; Vaughn,
1951; Geldreich, 1965) in which the emphasis has been shifted from the coliform group
as a whole to the E. coli bacteria only as being indicators of water pollution. The singling
out of the E. coli bacteria or fecal coliforms, as they are referred to, is usually done by
inoculating the water sample to be tested into one of the known selective media for E.
coli (Boric acid or mFC Difco) and incubating afterwards at 43°C or 44.5°C (as the
particular test requires). At these temperatures it is presumed that the non fecal coliforms
do not develop. This double selection (through media and temperature) seems to be
inadequate, especially in water bodies in which the pollution is not too high and the
recovery of every E. coli present is of importance.
Mishra (1968), in his study on the evaluation of elevated temperature tests pointed out
that not all the coliforms isolated from feces could be detected in this way. Rao (1968),
testing feces samples showed that in addition to E. coli type I, about 20% of other
coliforms were usually found. Burman (1961) in his studies showed that the incubation at
optimal temperature of the organisms is of outmost importance for the development of
these bacteria - and that this was around 37°C.
Bacteriophages are well known for their specific attachment to host bacteria (Adams,
1959). This characteristic is routinely used in medical laboratories for an accurate
identification of bacterial strains, for example phage typing of Salmonella (Sechter, 1967)
or epidemiological studies for the exact determination of the source of infection (Ross,
1966).
It has been shown that E. coli bacteriophages are very specific in their attachment to
host bacteria and because of that are suitable for use as identifiers of E. coli bacteria
(Buras, 1970). It seemed therefore, that the most reasonable method for the
identification of E. coli in order to determine water pollution would be to use a highly
selective medium (Buras & Kott, 1969) with optimal temperature incubation and
identification by specific bacteriophages.
The purpose of this research was to carry out a comparative study of conventional
methods with the method using E. coliphages as E. coli identifiers. The study was carried
out on a number of water bodies with various degrees of pollution.
73
N. BURAS and Y. KOTT
Environmental Engineering Laboratories, Technion,
Israel Institute of Technology, Haifa, Israel
INTRODUCTION
Although serious efforts are directed into developing ways and media for the isolation
and quantification of pathogens in water (Livingstone, 1965; McCoy, 1968; Moore,
1951), the most accepted method for the determination of the bacteriological water
quality is still the quantitative evaluation of the coliform group of bacteria as a whole
(Standard Methods, 1965).
Lately a number of new methods have been described (Perry et al, 1944; Vaughn,
1951; Geldreich, 1965) in which the emphasis has been shifted from the coliform group
as a whole to the E. coli bacteria only as being indicators of water pollution. The singling
out of the E. coli bacteria or fecal coliforms, as they are referred to, is usually done by
inoculating the water sample to be tested into one of the known selective media for E.
coli (Boric acid or mFC Difco) and incubating afterwards at 43°C or 44.5°C (as the
particular test requires). At these temperatures it is presumed that the non fecal coliforms
do not develop. This double selection (through media and temperature) seems to be
inadequate, especially in water bodies in which the pollution is not too high and the
recovery of every E. coli present is of importance.
Mishra (1968), in his study on the evaluation of elevated temperature tests pointed out
that not all the coliforms isolated from feces could be detected in this way. Rao (1968),
testing feces samples showed that in addition to E. coli type I, about 20% of other
coliforms were usually found. Burman (1961) in his studies showed that the incubation at
optimal temperature of the organisms is of outmost importance for the development of
these bacteria - and that this was around 37°C.
Bacteriophages are well known for their specific attachment to host bacteria (Adams,
1959). This characteristic is routinely used in medical laboratories for an accurate
identification of bacterial strains, for example phage typing of Salmonella (Sechter, 1967)
or epidemiological studies for the exact determination of the source of infection (Ross,
1966).
It has been shown that E. coli bacteriophages are very specific in their attachment to
host bacteria and because of that are suitable for use as identifiers of E. coli bacteria
(Buras, 1970). It seemed therefore, that the most reasonable method for the
identification of E. coli in order to determine water pollution would be to use a highly
selective medium (Buras & Kott, 1969) with optimal temperature incubation and
identification by specific bacteriophages.
The purpose of this research was to carry out a comparative study of conventional
methods with the method using E. coliphages as E. coli identifiers. The study was carried
out on a number of water bodies with various degrees of pollution.
73