viding more timely access to microbial
data and indications of emerging product and process issues. Improved
pathogen detection capability has enabled Quality and Operations Management personnel to identify, respond to
and correct problems proactively, working to prevent finished product failure.
New methods have created more options
for processors and have necessitated the
development of performance criteria to
aid in the method selection process: that
is, on what basis does a processor compare a variety of test methods and make
an appropriate, knowledge-based selection?
Three such criteria have emerged uniformly across the food industry—speed,
accuracy and ease-of-use. The former
compares “total time to actionable result” (TTAR), the amount of time that
elapses between sample availability and a
test result. Accuracy, in brief, can be defined as the new method’s agreement
with official test methods or gold standards. These comparisons are generally
made on the bases of sensitivity and
specificity, inclusivity and exclusivity,
limit-of-detection (LOD), false-positive
and false-negative rates and other parameters. Finally, ease-of-use relates to the
level of technical expertise required to
“Historically, pathogen reduction efforts
focused on the pre-release screening of finished
product.”
conduct the test method and the extent
of materials required (e.g., instruments
and consumables). In profiling the four
detection technologies currently available—cellular, immunological, molecular
and spectrometric—this article will additionally provide comparisons based on
the selection criteria cited above.
Which Test to Choose?
Dating to the earliest days of microbiology, cell culture detection and recovery methods for pathogens have evolved
in complexity, selectivity and effectiveness since the late 19th century. To the
extent that they ideally produce a visible
bacterial colony as their endpoint, cell
culture methods have long been considered the gold standard of microbiology.
In brief, the method involves the suspension of a sample in solution; the
preparation of an optimal bacterial
growth medium with appropriate nutrients, pH level and metabolic indicators;
the mixing or plating of the sample and
Quantifying Pathogen Testing
In a recently released market research report entitled Food Micro—2008 to
2013, Strategic Consulting estimates that over 738 million microbiology tests
were performed in 2008 by the food processing industry worldwide. Routine
microbiology tests [total viable organisms (TVOs), coliform, yeast, etc.] accounted for more than 80% of these tests.
In 2008, food processors around the globe ran approximately 138 million
tests (in total) for a variety of pathogens, which had a market value of over $1
billion. Of this total, tests for Salmonella were the most frequent, followed by
tests for Listeria, E. coli O157 and Campylobacter.
For further information about this report, please visit www.strategic-consult.com or contact Tom Weschler at 802.457.9933 or weschler@strategic-consult.com.
media in a petri dish, tube or similar vessel; the incubation of the mixture at an
ideal bacterial growth temperature for a
prescribed period of time; and finally, a
quantitative assessment of the presence
or absence of countable bacterial
colonies. Adjustments to any of the
above method components—nutrients,
pH level, indicators, incubation time or
temperature—may be made to alter the
selectivity and outcome of the assay. Fastidious bacterial targets, such as Listeria
spp., may require multiple enrichments
and platings in a variety of selective
media to reduce competitors and enable
recovery of the organism.
From the standpoint of speed, cell
culture methods may require from several days to a week or more to generate
confirmed and actionable test results. In
terms of accuracy, many are considered
official, confirmatory and/or gold standard procedures—that is, a visible colony
of the target organism is produced. The
ease-of-use of cell culture methods is arguable. A trained lab technician, exercising good laboratory practices (GLPs), is
needed for the sample and media preparations, the multiple test manipulations
and the interpretation of results. With
the exception of a scale, glassware, water
bath, autoclave and incubator, most of
the materials used in cell culture test
methods are consumable and disposable.
Many media are also commercially available in pre-prepared, ready-to-use formats, in addition to pre-poured,
sample-ready plates. At least two companies now offer a sample-ready film format that is pre-coated with the
appropriate desiccated media and simply
requires sample inoculation and incubation.
The award-winning work of Philip
Perlmann and Eva Engvall on immunoassays in 1970 at the University of
Stockholm enabled the emergence one
decade later of commercially available,
enzyme-linked immunosorbent assay
(ELISA) technology for rapid foodborne
