Escherichia coli, which is abbreviated as E. coli, refers to the rod-shaped bacterium that occur naturally in the lower intestines of endotherms, or warm blooded organisms, including human beings, as well as reptiles and fish. While most of these gram-negative organisms are harmless, some of the serotypes can result in serious food poisoning due to food contamination, which is a common reason for product recalls. There are five strains of E. coli that cause diseases. Some of these diseases include hemolytic uremia, copious bloody discharge, unique diarrhea, and Enterohemorrhagic (EHEC) class.
Importance
of E. coli Testing
While E. coli are basically harmless,
they exist in the same conditions that are conducive for human pathogens. As
such, microbiological
quality assurance tests check for these organisms in order to identifying
the effectiveness of effluent disinfection in nutraceutical and pharmaceutical products,
as well as on animal products and wastewater treatment plants. These organisms
are easily detectable, which implies that the impact of a particular treatment
in destroying various pathogens can be confirmed by the absence of E.
coli.
The growing use of E. coli as an
indicator can be attributed to the new techniques for microbiological testing
that employ rapid detection systems to detect them, in addition to its listing
in industry standards such as the U.S. Pharmaecopia. Current techniques produce
results in 3-7 days depending on the methodology used for different
industries.
Nutraceutical
and Dietary Supplements
According the U.S.
Pharmaecopia protocol <2022>, tests performed on 10 grams of a
product should not contain any E. coli. A 1:10 dilution of the product is
incubated at 30 - 35C for 24–48 hours, before 1.0 ml can be transferred to
MacConkey broth (10 ml). This mixture is then incubated at 42-44C for another
24-48 hours. Afterwards, part of the MacConkey broth is mixed with MacConkey
agar and incubated at 30-35C for 18-24 hours. In the event that typical
colonies appear, transfer them to Levine Eosin Methylene-blue agar and incubate
at 30-35C for 24-48 hours. Examine the colonies under reflected or transmitted
light. If you cannot detect a green-metallic shine or blue-black appearance
using either light sources respectively, it implies that the sample does not
contain E. coli.
Pharmaceutical
Microbiology
According the U.S. Pharmaecopia protocol
<62>, no
E. coli should be found in 10 grams of the product. A 1:10 dilution of the
product is prepared and incubated at 30-35C for 18-24 hours. 1.0 ml of this
mixture is then transferred to MacConkey broth (100ml) and incubated at 42-44C
for 24-48 hours. A loop is then transferred to MacConkey agar and incubated at
30-35C for 18-72 hours. The presence of E. coli is indicated by growth of
typical colonies, which is confirmed by performing an identification
test.
Food
Testing
Contrary to the other two industries, food testing adheres to the
Bacteriological Analytical Manual (BAM). The method used is MPN or most
Probable Number, which is a multi-step assay comprising a presumptive phase in
LST tubes, confirmation phase in BGLB tubes, and completed phase in EC tubes.
The assay consists of sequential dilutions of the sample product that are
inoculated in broth media. Gas positive scores from each of the phases are then
contrasted to a statistical table to obtain an estimate of the number of
organisms in the product.
E. coli grows poorly at 44-45C, which
makes it difficult to detect using conventional tests. In addition, it is
acid-tolerant with the ability to grow and survive at pH values as low as 3.6 –
4.4, though it can be destroyed by subjecting it to heat of about 70C for about
2 minutes (as is the case for certain foods). The unique characteristics of E.
coli cause traditional tests to be task intensive, and may still be unable to
detect the microorganisms in certain conditions.
Fortunately, current rapid testing
methodologies are simpler to perform, use less disposables and labor, and
enable a faster microbiology quality assurance process compared to traditional
methods. Rapid E. coli
tests are automated, accurate, deliver fast results in about 30 hours, and
minimize the possibilities of product interference.
Contact Biolumix to learn more
about E. coli testing.
Biolumix
3928 Varsity Dr.
Ann Arbor, MI 48108
Phone: (734) 984-3100
Fax: 734-222-1830
Email: info@mybiolumix.com
