Sample Processing - Waterborne Pathogens: Detection Methods and Applications - page 62

CHAPTER FOUR
Sample Processing
Helen Bridle 1 , Karin Jacobsson 2 , Anna C. Schultz 3
1 Heriot-Watt University, Institute of Biological Chemistry, Biophysics and Bioengineering, Riccarton,
Edinburgh, Scotland
2 Mikrobiologienheten, Uppsala, Sweden
3 DTU Food, National Food Institute, Technical University of Denmark, Mørkhøj Bygade, Søborg, Denmark
While this topic focuses on emerging methods for the detection of water-
borne pathogens, this chapter is devoted to sample processing which plays
a key role in the ultimate success of any detection technology. Many of the
techniques discussed in the following chapters process from microliters to a
few milliliters, whereas it may be necessary to sample hundreds of milliliters
to thousands of liters. Large sample volumes are required to gain a more
representative sample of a large water volume, as well as to increase the like-
lihood of detecting pathogens present at very low concentrations. Sampling
of a large volume over a period of time will, to some extent, compensate
for some spatial and temporal variations in pathogen distribution. Addition-
ally, the concentration aspect of sample processing is necessary to bring the
pathogen concentration into the detection limit of monitoring methods.
Furthermore, while some techniques would detect single pathogens the
time required for a single pathogen in a large volume of water to reach the
detection area/surface could be prohibitively long. Sample processing is also
important for isolation of the pathogen of interest and for removal of inter-
ferents which could disturb the detection process. The nature of problem-
atic interferents varies with the final monitoring technique employed and,
therefore, different sample processing methods may be required depending
upon the full scheme of detection.
This chapter will introduce different methods of sampling and give an
introduction to the basic processes behind different sample processing tech-
niques. The chapter is organized according to process order. First, initial
methods of concentration are presented followed by secondary concentra-
tion steps, which further reduce the volume and in some cases isolate the
pathogen of interest. There is some overlap between techniques used in
these stages. Next, a section is devoted to the extraction of nucleic acids
for detection by molecular methods. Analytical controls are important to
determine how well a process is working, in terms of recovery rate, and