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44 Emerging Bacterial Food-Borne Pathogens and Methods of Detection 847detection of fluoroimmuno-stained cells; bioluminescence with
IMS (Takahashi et al. 2000, Tu et al. 2000, Squirrel et al. 2002).DNA MicroarraysDNA microarrays consist of gene probes arrayed on a sub-
strate. Such arrays may be limited to select genes of interest
or be multigenome-wide in scope. Among other things, they
can be used for comparative genomic hybridization (also called
genomotyping), to study genome-wide gene expression or for
the detection of pathogens in a sample. They have quickly be-
come a powerful tool in genomic analysis of pathogens. The
microarray itself (often called a gene chip or biochip) consists
of a series of DNA molecules of known sequence called probes
that are fixed to a substrate (usually, a special type slide). These
probes consist of partial gene sequences, generated from PCR,
full-length cDNA, or oligonucleotides (Pagotto et al. 2005) of
the pathogens of interest. Such microarrays can be used to de-
tect a large number of pathogens in a sample or alternatively,
they can be used to perform expression studies of the whole
genome or select genes; for the purposes of this chapter we
will focus on the use of microarrays as a detection technology
only; for more detail regarding other applications of microar-
rays the reader is directed to reviews on the subject. A recent
review by Ojha and Kostrzynska (2008) highlights the applica-
tion of microarray technology in the field of veterinary research
for pathogen infection investigations, diagnostics, and studies of
host pathogen interactions. Similar research by Jin et al. (2005)
used microarray technology to investigateE. coliO157:H7.
Microarrays can also be used to assess similarities between
strains, characterize strains or subtype strains. Boyd et al. 2003,
Gaynor et al. (2004), Hain et al. (2006), Malik-Kale et al. (2007),
Parker et al. (2007), and Raengpradub et al. (2008) have de-
scribed the use of microarray technology to analyze strains at the
genetic level for comparative purposes. Volokhov et al. (2002),
(2003), Chen et al. (2005), Reen et al. (2005), Garaizar et al.
(2006), Anjum et al. (2007), Yoshida et al. (2007), Zhang et al.
(2007), Batchelor et al. (2008) have used microarrays to identify
various bacteria to species or subspecies level, detection of vir-
ulence or antimicrobial resistance genes and Call et al. (2001),
Chandler et al. (2001), Keramas et al. (2004), Kostrzynska and
Bachand (2006), Kostic et al. (2007), Quinones et al. (2007)
have used them for detection, identification, and characteriza-
tion of pathogens in a range of samples. Given the unlimited
amount of information available, microarrays can be designed
and built for a range of purposes such as, determining expres-
sion of specific virulence or antimicrobial resistance genes or
for more specific processes, such as study of invasion, flagel-
lar production, growth processes, or biofilm production. DNA
microarrays offer much promise for future studies in under-
standing pathogens, hosts, and production systems—they can
be used to model host–pathogen interactions and the effect of
various drugs or vaccines on a host or pathogen. Therefore, it
is likely that microarray technology will provide needed insight
into faster methods for detection and understanding the mech-
anisms of pathogenesis used by food-borne pathogens that can
be exploited to make food safer.Immunosensors or BiosensorsBiosensors are analytical devices that convert a biological re-
sponse into an electrical signal. Biosensors work on the principle
of a biological component that is coupled to a physiochemical
type transducer that collects signal and converts it to an elec-
tronic readout. A range of bioreceptors currently recognized for
use in pathogen detection include antibodies, enzymes, nucleic
acids, cellular, biomimetic, and bacteriophages (Velusamy et al.
2010). Biosensor technology has rapidly expanded in the last
10 years and as this chapter is completed, there will no doubt
be many more new applications emerging. Some of the more
promising technologies at this point are based on fiber optics
and electrochemical reactions. Velusamy et al. (2010) provide a
comprehensive overview of sensors for application in pathogen
detection.Fiber Optic BiosensorOptical fibers for the detection of pathogens work on the prin-
ciple of a fiber optic taper that sends excitation laser light to a
detection surface and receives emitted light. As such, fiber optic
technology has been reported to be very useful in the detection
of food-borne pathogens. Optical biosensors measure changes
in refractive index, fluorescence emission or quenching, chemi-
luminescence, and fluorescence energy transfer. One such fiber
optic biosensor operates by using an antibody sandwich format
on optic fiber to detect the capture of antigens using fluorescently
tagged conjugates. Geng et al. (2004) used a fiber optic-based
detection system to detectListeriain mixed cultures, and meat
sample enrichments with a detection level as low as 10–10^3
cells/mL. In a similar type approach, Kramer and Lim (2004)
developed a rapid automated fiber-based biosensor for the detec-
tion ofSalmonellain sprout rinse water. The sensor was capable
of detectingSalmonellawhen counts as low as 50 CFU/g were
inoculated into the seeds. Fiber optics have been used inListeria,
Salmonella,E. coliO157:H7, andClostridium botulinumtoxin
detection (Ogert et al. 1992, Strachan and Gray 1995, Simpson
and Lim 2005, Ko and Grant 2006) and for the detection of
S. aureus(Chang et al. 1996).Raman and Fourier Transform SpectroscopyThis technology is frequently used in whole organism finger-
printing but also has application in analysis of a sample of
interest. The technique does, however, depend on increasing
the population so that there is sufficient amount for biomass
analysis. Raman spectroscopy is an optical technique that uses
light scattering to detect pathogens (Schmilovitch et al. 2005).
Modifications of Raman spectroscopy using surface enhanced
technologies (Grow et al. 2003, Kalasinsky et al. 2007) have
also been developed (see below).Fourier Transform Infrared SpectroscopyFourier transform infrared spectroscopy (FTIR) is a nondestruc-
tive technique for pathogen detection that measures infrared loss