Listeria monocytogenes transfer during slicing of delicatessen meats

Dr. Elliot RyserDepartment of Food Science and

Human NutritionMichigan State University

East Lansing, MI

September 14, 2011

Listeriosis Outbreaks Traced to Listeriosis Outbreaks Traced to Delicatessen-Sliced TurkeyDelicatessen-Sliced Turkey

May – Dec 2000: 16.9 million lbs recalled

29 cases

4 deaths

3 miscarriages

June 2001: 16 cases of acute febrile gastroenteritis (no deaths)

October 2002: 27.4 million lbs recalled

46 cases

7 deaths

3 miscarriages

Predicted Annual Listeriosis Cases (Log Scale) from Different Food Scale) from Different Food Categories in Categories in the United States (FDA/FSIS, 2003)the United States (FDA/FSIS, 2003)

DM = Deli meats; FNR = Frankfurters (not reheated); P= Pâté and Meat Spreads; UM= Unpasteurized Fluid Milk; SS= Smoked Seafood; CR = Cooked Ready-To-Eat Crustaceans; HFD = High Fat and Other Dairy Products; SUC = Soft Unripened Cheese; PM = Pasteurized Fluid Milk; FSC = Fresh Soft Cheese; FR = Frankfurters (reheated); PF = Preserved Fish; RS = Raw Seafood; F = Fruits; DFS= Dry/Semi-dry Fermented Sausages; SSC = Semi-soft Cheese; SRC = Soft Ripened Cheese; V = Vegetables; DS = Deli-type Salads; IC= Ice Cream and Frozen Dairy Products; PC = Processed Cheese; CD = Cultured Milk Products; HC = Hard Cheese.

USDA Listeria Alternatives Implemented October 2003

Deli Deli Meat Recalls, 1994 - 2005Meat Recalls, 1994 - 2005

0

2

4

6

8

10

12

1994 1995 1996 1997 1999 2000 2001 2002 2003 2004 2005 2006

Year

Nu

mb

er o

f re

calls

Ham

Turkey

Chicken

Beef

Corned Beef

Other

> 84 recalls> 53 million lbs

Year Number of Recalls

Recalled Product (lbs)

2006 1 3752007 3 86002008 7 16,0002009 3 39,0002010 6 170,0002011 6 9,500

10

Gombas et al., 2003 0.4% of manufacturer-sliced 2.7% of delicatessen-sliced

Draughon et al., 2006 0.2% of manufacturer-sliced 1.4% of delicatessen-sliced

Deli-sliced meat still 7 times more likely to be contaminated

Sales 24.4% manufacturer-sliced 75.6% delicatessen-sliced

Current ConcernsCurrent Concerns

~ 1,600 listeriosis cases annually including ~255 fatalities~ 290 of 1,600 listeriosis cases from deli

meats: ~ 42 pre-sliced, ~ 248 deli-sliced~ 46 fatalities from deli meats~ 6 fatalities from pre-sliced~ 40 fatalities from deli-sliced

Raw materials

Manufacture Slicing Food contact

surfaces Packaging

Retail Slicing Product handling Deli environment

Consumer Refrigerator Slicing Product handling Environment

Contamination primarily occurs after processing

Distribution of Distribution of ListeriaListeria spp. in spp. in

a Local Deli/Restauranta Local Deli/Restaurant------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Location Listeria L. seeligeri L. innocuaL. mono------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Basement 35 20 7 8

Kitchen 50 27 11 12

Front line 7 7 0 0

Sandwich line 20 9 8 3

Seafood case 5 0 5 0

Cheese case 9 4 5 0

Meat case 7 4 3 0

Display floor 10 3 2 5

Open back case 1 1 0 0

Board (meat, cheese) 10 1 9 0

Slicer (Hobart, sandwich line) 8 7 0 1

Slicer (Bizerba, deli) 5 4 0 1

Slicer (Bizerba, cheese) 2 2 0 0

Slicer (Hobart, basement sandwich line) 0 0 0 0

Slicer (Hobart), basement, cheese 1 1 0 0------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Total 170 90 50 30------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

_________________________________________________Location Listeria pos/ # of positive visits

# tested (%) Listeria LM_______________________________________________________Basement 35/70 (50) 13 4Kitchen 50/84 (60) 14 6Front line 7/42 (17) 4 0Sandwich line 20/56 (36) 14 3Cases(meat, cheese 42/154 (27) 13 5floor, seafood)Slicer (H,SL) 8/70 (11) 4 1Slicer 1(B,deli) 5/70 (7) 2 1Slicer 2(B,deli) 2/70 (3) 1 0Slicer 1/103 (1) 1 0(Cheese, basement)Slicer 0/70 (0) 0 0(meat, basement) _________________________________________________________________

1.1. Transfer of Transfer of L. monocytogenesL. monocytogenes to to different components of a deli slicerdifferent components of a deli slicer

2. L. monocytogenes transfer to deli meats during slicing

3. Impact of biofilm formation and sublethal injury on Listeria transfer to deli meats

4. Development of a risk assessment for L. monocytogenes in deli meat

Back plate

Table

Guard frontGuard back

Collection area

Blade

Guard holder

Hobart Berkel

Food Residue Behind the BladeFood Residue Behind the Blade

Product inoculation and slicing 1-cm strip on surface of product inoculated to

contain L. monocytogenes at 108 CFU/cm2 Held 1 hour at 5°C before slicing

Sampling method after each slice 1-ply composite tissue method (Vorst et al.

2004. J. Food Prot. 67:2212-2217)

-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

Collecti

on a

rea

Back

plate

Table

Blade

back

Blade

front

Guard

bac

k

Gurad

fron

t

Blade

table

Guard

hold

er

Lo

g C

FU

Hobart blade 1 Hobart blade 2 Berkel blade

Other components of the slicer will be contaminated if a positive product is sliced on a commercial machine, not just the product being sliced

1. Transfer of L. monocytogenes to different components of a deli slicer

2.2. L. monocytogenesL. monocytogenes transfer to deli transfer to deli meats during slicingmeats during slicing



• Slicer blade to product

• Product to slicer blade to product

Slicer blade inoculated with a turkey slurry to contain ~103, 105, and 108 Lm CFU/blade

Held 1 hour at 21 – 23°C before slicing

3 replicates

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 2 4 6 8 10 12 14 16 18 20

slice

Lo

g C

FU

/slice

Turkey

Salami

Bologna

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5

10

15

20

25

0 5 10 15 20 25 30

Slice number

Cu

mu

lati

ve

Tra

ns

fer

(%)

Turkey

Salami

Bologna

103 CFU/blade Turkey: Slice

28 Bologna: Slice

20 Salami: Slice

23• Except for salami, 99% of the original L. monocytogenes population is transferred in the first 10-15 slices, but much is unaccounted for.Assumption is that Listeria is spread into the immediate environment, remains on the blade or dies offWith salami continual transfer likely exceeds 30 slices

Products– turkey, salami, bologna Surface inoculated to contain 105 and

108 CFU/cm2 1-cm strip on the product surface Held 1 hour at 4.5°C before slicing

Slicer inoculation Inoculated product sliced 5 times to

contaminate the blade at approximately 103 and 105 CFU/blade

Product transfer Uninoculated product sliced sequentially 24 - 36 replicates

0.0

0.5

1.0

1.5

2.0

2.5

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3.5

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4.5

5.0

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Slice number

Lo

g C

FU

/slic

e

IT-US

IS-UT

IS-US

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20

Slice number

Cu

mu

lati

ve T

ran

sfer

(%

)

IT-UT

IT-US

IS-UT

Salami followed by salami Slice 30

Salami followed by turkey Slice 10

Turkey followed by salami Slice 17

-1

0

1

2

3

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5

26-3

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31-3

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36-4

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41-4

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46-5

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66-7

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76-8

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81-8

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86-9

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91-9

5

96-1

00

Lo

g C

FU

/gro

up

Berkel bladeHobart blade 2Hobart blade 1



3.3. Impact of biofilm formation and Impact of biofilm formation and sublethal injury on sublethal injury on ListeriaListeria transfer to transfer to deli meatsdeli meats


Conditioning layer: meat, meat exudate

Unlikely to meet moisture requirement will rely on RH of the operation and food

products for moisture Cleaning and friction from slicer will

disrupt biofilms Attached bacteria and food particles

likely, but not biofilms

Persistent strains of L. monocytogenes attach to food contact surfaces and form biofilms more readily than non-persistent strains

Sublethal injury enhances resistance of Listeria to environmental stresses and leads to more persistent strains

L. monocytogenes strains Strong and weak biofilm

formers Healthy, starved, cold-

stressed and chlorine-injured

Inoculate to contain ~108 CFU/blade

Allow to dry, incubate blades in humidity chamber at 78% RH, 22°C, 6 and 24 h

24 replicates for healthy and cold-injured models each, and 36 replicates all others combinations

Sequential Transfer to Turkey, Healthy

00.5

11.5

22.5

33.5

4

0 5 10 15 20 25 30

Slice number

Lo

g C

FU

/sli

ce Strong, 6 h

Strong, 24 h

Weak, 6 h

Weak, 24 h

Transfer of Uninjured Transfer of Uninjured L. monocytogenes L. monocytogenes to Salamito Salami

0.0

1.0

2.0

3.0

4.0

5.0

0 5 10 15 20 25 30

Slice number

Lo

g C

FU

/slic

e

Strong, 6 h

Strong, 24 h

Weak, 6 h

Weak, 24 h




4.4. Development of a risk assessment for Development of a risk assessment for L. monocytogenesL. monocytogenes in deli meat in deli meat

Risk Assessment Risk Assessment FrameworkFramework

Hazard Identification

Exposure Assessment

Hazard Characterization[Dose-Response]

Risk Characterization

Description of the Hazard (agent in the food) And adverse effects

What is the probability of consuming contaminated food AND what are the likely numbers of a pathogen in the food at the time of consumption

A mathematical model which predicts theprobability of an adverse effect from a given dose.

• Provides a RISK ESTIMATE• What is the nature andlikelihood of the health risk?• Who and how many arelikely to become ill?• What are the sources ofvariability and uncertainty inthe information used?

Jaykus et al. 2007

Contamination Levels at retail (cfu/g)

Growth in the retail refrigerator

Contamination level atconsumption (log CFU)/g)

Contamination level per serving

Lag time Growth rate Storage time Refrigeration temperature Maximum growth

Serving size

Enumeration dataL. monocytogenes distribution in food

Prevalence

Initial contamination level (log cfu/g)

Cross contamination during deli slicing

Growth in the home refrigerator

L. monocytogenes transfer rate product composition type of slicer blade

Left-overportions

% frequency data

Jaykus et al. 2007

Slicing a contaminated product will lead to contamination of all slicer components

> 90% of Listeria transfer from the blade to the product occurs during the first 10-15 slices of delicatessen meats after mechanical or knife slicing

Deli meats will “clean” the slicer blade, but with varying effectiveness

Additional Factors Impacting Listeria Transfer

Product composition Moisture, Fat

Product temperature Order in which products are sliced Model and design of the slicer Characteristics of L. monocytogenes

Healthy vs. injured Strong or weak biofilm former

Avoid the first 10 slices?

Do opened packages of non-recalled product pose a significant risk?

• Dr. Keith L. Vorst• Dr. Lindsey Keskinen• Dr. Zhinong Yan• Dr. Bradley P. Marks• Dr. Ewen Todd• Dr. Gary Burgess• Amanda Benoit

Funding FDA USDA-NAFSS USAD-NISFI

Referencec : www.slideshare.com

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Listeria monocytogenes transfer during slicing of delicatessen meats

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