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652 Sonderthema: Mikrobiologische Methoden in der Lebensmittelanalytik «
Microorganisms in liquid samples
Simple testing options exist to detect or
enumerate microorganisms
Rolf Steinmüller
Testing liquid samples, including water, for microorganisms presents challenges not
seen in testing other sample types. Water samples often contain viable microorganisms
injured by chlorine treatment, and liquid samples in general present a challenge to collect
representative test samples. We offer a choice of test systems to detect, or enumerate,
microorganisms in challenging liquid samples.
Dr. Rolf Steinmüller
» Contact
Dipl.-Biologe, Division
Manager Germany,
Neogen Europe Ltd.
«
The Colitag (Presence/Absence) Water
Test Kit uses an U.S. Environmental Protection
Agency (EPA)-approved selective
and differential medium to detect total
coliforms and E. coli in water and liquid
samples in as little as 16 hours.
The Filter is a disposable membrane
filtration system that uses ampouled media
to detect and provide quantitative
results for a wide variety of microorganisms
in liquid samples. The new disposable
system utilizes cellulose membrane
filter technology, and ampouled liquid
media, to detect and quantify target organisms.
The system is available with either
white or black filters, and each lid has
a magnifying circle to make the small colonies
easier to identify. Various 2 mL media
ampoules are available for use with
the system to detect a variety of microorganisms
in a variety of liquid sample types.
A testing method to detect
coliforms and E. coli in water
Colitag represents the next generation of
tests to detect potentially dangerous coliforms.
Unlike other tests, Colitag’s patented
system resuscitates and detects chlorine-injured
coliforms, including E. coli.
Other tests can miss these weakened coliforms,
which may include bacteria capable
of causing human illness.
The system allows users to easily go beyond
simple coliform detection at the level
of 1 colony forming unit (CFU) per 100 mL.
It also allows the simultaneous identification
of the coliform of utmost concern,
E. coli. Simply detecting coliforms provides
a good indication of the overall sanitation
level of a facility. But, solely detecting
coliforms does not indicate whether
the coliforms that were found are innocuously
environmental, or the more potentially
dangerous E. coli.
Fecal coliforms and E. coli can be detected
using the Colitag system, if
4-methylumbelliferyl-β-D-glucuronide
(MUG) positive E. coli are present in the
sample, a bright blue fluorescence will be
seen when subjected to ultraviolet light.
The sample may also be checked for indole
positive E. coli, by adding Kovac’s reagent.
A reddish-purple colour will form on the
surface of the solution with the presence
of indole positive E. coli.
After a single 24-hour incubation, and
with very little extra effort, the assay
allows users to go beyond coliform de-
» Dezember 2012 | DLR