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Frequently Asked Questions
1. What is the main principle of the Bactometer?
2. What is the sensitivity/detection limit of the
Bactometer? How is that different from the threshold of the system?
3. What are the types of test that can be performed
by the Bactometer?
4. Why is there a shelf life for the Bactometer
module, and is it reusable?
5. Is it required to prepare a standard curve for
every product so that the CFU can be determined based on the detection
time?
6.What is the difference between dilute to specification
and functional sterility?
1. What is the main principle of the Bactometer?
The main principle of the Bactometer is impedance microbiology,
which is the measurement of bacterial growth by monitoring the
movement of ions between electrodes (conductance), or the storage
of charge at the electrode surface (capacitance). Impedance microbiology
combines kinetic detection with traditional bacteriological media
for the enumeration of total bacteria, yeasts and molds, as well
as selectively monitoring for coliforms, lactic acid bacteria,
anaerobes and pathogens. As bacteria grow, they metabolize larger
weakly charged molecules (polysaccharides, fats, proteins) and
produce smaller charged metabolic by-products (organic acids,
fatty acids, amino acids). Impedance remains relatively constant
until the numbers of microorganisms present in the sample reach
a measurable electrical threshold.
2. What is the sensitivity/detection limit
of the Bactometer? How is that different from the threshold of
the system?
The Bactometer sensitivity is one viable CFU per sample well.
One CFU bacteria is generally detected in 9 hours where 1 CFU
of yeast can be detected in 19 hours. Although the Bactometer
can detect as little as 1 CFU per well, organisms must first grow
to a detectable level or threshold for the system to detect. The
threshold is defined as the number of organisms needed before
the instrument can make detection. The threshold for bacteria
is 100,000 CFU and the threshold for yeast/mold is 10,000 CFU.
The rate of the detection time is dependent on the initial concentration
of organisms in the product sample.
3. What are the types of test that can be
performed by the Bactometer?
The Bactometer incorporates testing with non-selective and selective
media that allows the detection of total aerobic plate count,
coliforms, yeast and mold, and lactic acid bacteria. The growth
of organisms can be incubated in the Bactometer at temperatures
of 15°C to 55° C such that a variety of flora can be detected.
4. Why is there a shelf life for the Bactometer
module, and is it reusable?
The shelf life for the module is 6 months. The module contains
stainless steel electrodes that allows for independent measurement
of the conductance and capacitance signal used in impedance detection.
The electrode is chemically conditioned to provide uniform performance
with a variety of media and products. The module should not be
reused or used after the expiration date.
5. Is it required to prepare a standard curve
for every product so that the CFU can be determined based on the
detection time?
A standard curve or calibration can be prepared for a given product
or group of products if the products are processed similarly and
the same flora are expected in the sample. For example a protocol
for raw meats and pasteurized milk would need to be calibrated
separately. However, where few organisms are expected (< 10
CFU), a calibration is not recommended. A more simple approach
of presence/absence is performed after the product has been diluted
in appropriate detection medium. (See question 6).
6.What is the difference between dilute to
specification and functional sterility?
A dilute-to-specification protocol dilutes the sample to the
required specification limit for product action or release. If
there is growth, the sample fails. If there is no detection, the
sample passes because the count is below the specification limit.
In a functional sterility application there is no allowable limit
and the product is not expected to contain any bacterial organisms.
Therefore, in a functional sterility application a pre-incubation
time is incorporated into the protocol. The pre-incubation time
is based on the target microflora. For total count, a pre-incubation
of 3-4 hours is recommended. For yeast/mold applications, a pre-incubation
of 18-24 hours is recommended.
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