Advancing Rapid Microbial Testing

7/30/2019 Advancing Rapid Microbial Testing

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pg 6868 09.06 www.ift.org

[ L A B O R A T O R Y ]

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

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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.

[email protected]

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.

Advancing Rapid Microbial Testing

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