Biology Reference
In-Depth Information
4.6.1. Analytical controls in molecular detection
Whenever possible, analytical controls should be included in the sam-
ple processing. For molecular detection, these normally include process
controls and amplification controls (
Table 4.3
). This is also illustrated in
Fig. 4.10
using viruses as an example. A control panel of model organ-
isms representing bacteria, viruses, and parasites can be used to moni-
tor the overall efficiency to recover the microorganisms from the three
kingdoms from different types of waters (treated as well as untreated
ground and surface waters) when using a specific combination of pro-
cessing steps (concentration, elution, and extraction). Positive process
controls are used to measure the recovery of target pathogen during the
whole extraction and test procedure, thus evaluating the efficiency of
the method as well as the error in human performance.
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When choos-
ing a heterologous microbe as process control, it is important that such
microbes simulate the recovery of the target organism from the water
sample as much as possible during sample treatment, but at the same
time they are unlikely to be naturally present.
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For example, for detec-
tion of enteric viruses, a number of nonenveloped positive sense single-
stranded RNA viruses have been suggested as process controls, such as
coliphage MS2,
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feline calicivirus,
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mengovirus strain (MC
0
),
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and
murine NoV.
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D'Argostino and co-workers performed a comprehensive
description of analytical controls used for virus detection in environmen-
tal samples from which the process and analytical controls are summarized
and broadened also in part to cover bacteria and parasites in the below
sections.
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4.6.1.1. Process controls
Process controls are used to control both sample treatment and test pro-
cedure and should therefore ideally be included at the beginning of the
actual sample treatment. However, in on-line sampling, or sampling directly
from tap in an outbreak situation, it is not possible to add controls before
sampling. Instead, they may be added after sample elution.
Sample Process Control (SPC)
is added to every test sample and to the
Target-Negative Process Control sample (TNPC, see below), ideally at
the start of analysis. It verifies if sample treatment has functioned cor-
rectly and identifies those samples in which sample treatment has failed.
The SPC must be detected in every sample. If the SPC cannot be added
to sample before concentration, it will only verify the step following its
addition.
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