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b y L i n d a L . L e a k e
So many rapid microbial tests, so lit tle time. That s
at once the dream come true and dream to come
o scientists everywhere. Faster methods and
continually emerging technologies have revolution-
ized microbial testing in recent years, slashing rst
hours, then days, o the time to get results.
Rapid testing is gaining momentum nationally and
internationally as an area o research and as a reliable
tool to monitor the kinds, numbers, and metabolites
o microorganisms related to ood spoilage, ood
preservation, ood ermentation, and ood saet y, says
Daniel Y. C. Fung ([email protected]), Proessor
o Food Science in the Dept. o Animal Sciences andIndustry at Kansas State University, Manhattan,
and a leading authority on rapid microbial testing.
Routinely traversing the globe to give lectures, con-
duct workshops, and discuss the role o rapid testing o
ood or saety and security, as well as o water, environ-
mental, air, industrial, and medical specimens, Fung lives
and breathes 24/7 with his nger on the pulse o whats
happening all over the planet relative to this hot topic.No one knows exactly how many microbio-
logical tests are done annually in the world, but the
number is increasing, Fung says. Based on dataavailable at this moment, about 3 3% o all test ing
is done in North America, 33% in Europe, and 33%
in the rest o the world. But in the next 1015 years,
the dynamics will change to 25% in North America,
25% in Europe, and 50% in the rest o the world.
He adds that his native China, with a population
o 1.3 billion, will set a bold new pace. When
China opens up to rapid testing, the market will
be huge. Southeast Asia, South America, Arica,
the Middle East , and the Pacic Rim will also
contribute to market growth in the years ahead.
Multi-Billion-Dollar IndustryAccording to the market report Food-Micro 2005
published by Strategic Consulting, Inc., Woodstock,
Vt. (w ww.strategic-consult.com), the global
market currently includes more than 625 million
ood industry microbiological tests completed in
200 5, with a market value exceeding $1.65 billion.
The ood sector represents the largest market
segment within the industrial microbiology market
and represents almost 50% o the total market, says
Thomas Weschler ([email protected]),
SCI President. The ood sector is more than double
the size o any other industrial segments, including the
pharmaceutical, beverage, environmental, industrialprocessing, and personal-care products sectors.
Since 1998, the market value or ood microbiology
has grown signicantly and has had an annual growth
rate o 9.2%, Weschler points out. Based on SCI
research, the ood microbiology testing market is
expected to grow to 822 .8 million tests in 2010 with a mar-
ket value o $2.4 billion, he relates. This represents a
projected annual growth rate o 5 .6% in test ing volume.
Driving this growth worldwide is an increase in ood
consumption, consumer demand, industrys ood saet y
priorities, and regulation, Weschler says. The accelera-
tion o the conversion o tradit ional microbiological
test ing methods to rapid methods is a unction o thosephenomena. It s no surprise that, despite the higher
Advancing RapidMicrobial Testing
Purdue University microbiology professor Arun Bhunia (standing) andpostdoc toral rese archer Padm apriya Ban ada are usin g asystem that analyzes scattered laser light to quickly identifybacteria in food samples.Photo by Tom Campbell, courtesy of Purdue Universi ty
Faster methods and continually emerging technologies
have revolutionized microbial testing in recent years.
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cost per test, these newer methods
are being used more requently
because they provide aster results
and/or ease-o-use benets
compared to traditional testing.
Nonetheless, traditional methods
still account or approximately
65% o the microbiological tests
perormed worldwide in the ood
market. Rapid counterparts, includ-
ing convenience-based (Petriflm,
or example), immunoassay-based,and molecular-based methods,
account or 3 5%, amounting to
220 million tests/year. Some
50% or more o all tests are run
to determine non-pathogens or
indicator organisms, according
to Food-Micro 2005.
By 2010, much will have
changed, says Weschler.
Traditional methods will still be the
predominant ones used, accounting
or 428.2 million tests/ year. However,
in 2010 traditional methods willrepresent only 52% o all tests
conducted, which is a reduction
o 12.4% rom 2005 based on
percentage o tests perormed.
All types o rapid methods
will make signicant gains in
usage during the coming ve-year
period, Weschler continues.
When combined, the annual test
volume o rapid methods will almost
double rom current levels and reach
394 .6 million tests in 2010, he elabo-rates. The gain in market value or
rapid methods will be even more
pronounced than t he test ing-volume
increases, since the rapid methods
have much higher average prices
per test than t raditional methods.
With such solid growth
prospects, the ood sector
is a market segment that all
diagnostic manuacturers need to
understand and, where they are
not currently present, possibly
enter, Weschler advises.
Reality Check
Despite these developments, its
critical to keep the big picture in
perspective, says Michael Doyle
([email protected]), a ood microbi-
ologist and Director o the Center
or Food Saety at the University o
Georgia, Grin. Rapid methods to
Rapid Microbial Testing continued...
Oxoid Ltd., Hampshire, UK
(www.oxoid.com), has designed
the Oxoid Listeria Rapid Test
or the detection o Listeria
species in many di erent oods,
including dairy, raw vegetables,
meats, poultry, and sh. The
procedure includes the use
o two enrichment broths or
the maximum recovery and
growth o Listeria ollowed by an
immunoassay using the testing
device. Ater adding the sampleto the testing device, result s
are available in about 20 min. A
blue line in the result window on
the testing device is a positive
result and indicates the pres-
ence o Listeria fagella antigen.
3M, St . Paul, Minn.
(www.3m.com), introduced
the 3M Petriflm EL Plate, a
sample-ready culture medium
that allows or the detection
o Listeria species, including
Listeria monocytogenes.The results can be inter-
preted quantitatively, which
could help identiy hot spots
and contamination sources. It
provides results in about 30 hr
rom the time o sample collec-
tion. An addit ional att ribute o
this testing kit is that is requires
no enrichment, which means
less risks o cross-contamina-
tion due to culture transers.
Whatman plc, Florham
Park, N.J. (www.whatman.
com), oers the FTA
Concen-trator-PS, a portable two-stage
lter co-developed with the
Food and Drug Administration
that can detect Cryptosporidium,
Giardia, Cyclosporia, and other
dangerous parasites in resh
produce and water supplies.
The eld test , which will be
used primarily by regulatory
agencies and municipalities,
takes as lit tle as 15 min, and
denitive results can be
obtained the same day.The device uses FTA, a
proprietary chemically treated
matrix that rapidly isolates
and protects nucleic acids atroom temperature. The sample
is passed through the matrix,
concentrating and destroy-
ing parasites. The device
immobilizes and preserves
the organisms DNA , which
can be tested with a simple
polymerase chain reaction
to conrm the presence o
any number o parasites.
Sword Diagnostics, Inc.,
a new company based at the
National Center or Food Saetyand Technology, Chicago, Ill.
(www.sworddiagnostics.com),
announces its groundbreak-
ing benchtop rapid test or
environmental Listeria that
provides results in just 16 hr.
The Saber Detection System
combines immunoassay capture
with Raman detection, an
advanced optical technique
that measures wavelength
shits . This system has the
ability to detect the presenceo microorganisms in concentra-
tions start ing at 102/mL.
Purdue University
researchers have developeda new system Bacteria Rapid
Detection Using Optical Scat-
tering Technologythat analyzes
scattered laser light to quickly
identiy bacteria or applications
in medicine, ood processing,
and homeland security,
reportedly at one-tenth the cost
o conventional technologies
(Bayraktar et al., 2006).
With this system, photons
bounce o o the colony, and
the pat tern o scat tered lightis projected onto a screen
behind the Petri dish. This
light-scatter pattern is
recorded with a digital camera
and analyzed with sophisticated
sotware to identiy the types
o bacteria. Using this method,
it takes less than 5 min to
identiy harmul organisms.
To date, the system has been
proven to accurately identiy six
species o Listeria, plus select
species o Salmonella , Vibrio,Escherichia coli, and Bacillus.
Recently Released Rapid Tests
Samples are addedtothe Saber DetectionSystem for automatedsample processing.
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Decagon Devices
1/2 ISL 4C
detect pathogens are still not rapid, he purports .
Most methods require 824 hr to get results.We need to get it down to less than 15 min.
Progress is being made toward that goal,
he says. The Food and Drug Administra-
tion, U.S. Dept . o Agriculture, and the ood
industry have initiatives to promote ood saety
programs based on Hazard Analysis and Critical
Control Points (HACCP) principles, he points out.
That work can benet greatly rom real-time
microbial tests that take minutes, not all day.
Thus ar, Doyle says, no test is sensitive
enough to match the regulatory gold standard o
one detectable target organism in a 25-g sample.
We currently need 103105 target bacteria/mLsample to detect target organisms, he relates.
Scientists are get ting the minimum down
to 103/mL, but we still need better ways to
concentrate bacteria to increase sensitivity,
Doyle emphasizes. Breakthroughs in this regard
should be orthcoming in the next ew years.
Catherine Donnelly (catherine.donnelly@
uvm.edu), Proessor o Microbiology in the Dept.
o Nutrition and Food Sciences at the University
o Vermont, Burlington, is energized by current
rapid test happenings and the prospects o
new developments. Its a really exciting time
to be a ood microbiologist , she says. Theadvantages testing technology provide are
outstanding. Rapid tests are user riendly,
accurate, and approved by AOAC International.
There are a variety o options or users.
Embracing reality in her renowned work
with Listeria, Donnelly is quick to point out
that rapid microbial testing is character-
ized by good news and bad news.
The good news is the technology, she
explains. The bad news is that some equip-
ment and instruments come with a het y price
tag. Some rapid test s are more cost e ective
than others. But it s important to keep inmind that some expensive instruments are
cheaper than employing and training a person
to do less-expensive testing methods.
Theres additional good news or most o theood industry, Donnelly saystheres not much
dierence in results between expensive tests
and inexpensive tests, so users can decide what
is most appropriate or their specic budget.
The blue line in this rapid test indicates the presence ofListeria.Photo courtesy of Kansas State University
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Rapid Microbial Testing continued...
Enrichment Essentials
The all-important enrichment step the time it takes to
grow pathogens to detectable levelsis the greatesthindrance to rapid microbial testing, says Dong-Hyun Kang
(oodsaety_2 [email protected]), Associate Proessor o
Food Science in the Dept. o Food Science and Human
Nutrition at Washington St ate University, Pullman.
Most enrichment steps take so much time that
we dont get test results or 102 4 hr, Kang says.
I we can nd a really good stimulant or a bacterial
target or a pat hogen we can decrease the enrich-
ment time to 46 hr. So its critical to ocus more
research on reducing the enrichment time. FT
Denver Instruments1/2 Horiz No Bleed
Linda L. Leake, Contr ibutin g Editor,Food Safety Consultant,
Wilmington, N.C.
Top-Ten Attributes of an Ideal Rapid Test
Daniel Y. C. Fung, Proessor o Food Science, Kansas State University,
Manhattan, says that many actors contr ibute to making a rapid test idealto use.
1. Accurate for the intended purposes. It considers sensitivit y, minimal
detectable limits, specicity o test system, versatilit y, potential applica-
tions, and comparison to reerence methods.
2. Speedy and productive. It includes time in obtaining results and the
number o samples processed per run, per hour, and per day.
3. Cost effective. The initial, per-test, reagent, and labor costs are
reasonable.
4. Acceptable. It is acceptable by the scientic community and regula-
tory agencies.
5. Simple to operate. The test takes into consideration sample prepa-
ration, operation o test equipment, and computer versatility.
6. Amenable to training. Location (on or o site), length o t ime, andqualications o operator are all actors.
7. User-friendly reagents. Preparation, stability, availability, and
consistency o reagents need to be considered.
8. Great company reputation.
9. Exceptional technical service. Speed, availability, cost, and scope
all count.
10. Optimum utility and space requirements.
R E F E R E N C EBayraktar, B., Banada, P.P., Hirleman, E. D., Bhunia, A.K., Robinson,
J.P. and Rajwa, B. 2006. Feature ext raction rom light-scatter patterns oListeria colonies or identifcation and classifcation. J. Biomedical Optics.11(3): 034006.