Listeria monocytogenes transfer during slicing of delicatessen meats

Dr. Elliot Ryser Department of Food Science and Human Nutrition Michigan State University East Lansing, MI September 14, 2011

Listeriosis Outbreaks Traced to Delicatessen-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 Categories in 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 Meat Recalls, 1994 - 2005 0 2 4 6 8 10 12 1994 1995 1996 1997 1999 2000 2001 2002 2003 2004 2005 2006 Year Number of recalls Ham Turkey Chicken Beef Corned Beef Other > 84 recalls > 53 million lbs

Year Number of Recalls Recalled Product (lbs) 2006 1 375 2007 3 8600 2008 7 16,000 2009 3 39,000 2010 6 170,000 2011 6 9,500

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 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 Listeria spp. in a Local Deli/Restaurant ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Location Listeria L. seeligeri L. innocua L. 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 4 Kitchen 50/84 (60) 14 6 Front line 7/42 (17) 4 0 Sandwich line 20/56 (36) 14 3 Cases(meat, cheese 42/154 (27) 13 5 floor, seafood) Slicer (H,SL) 8/70 (11) 4 1 Slicer 1(B,deli) 5/70 (7) 2 1 Slicer 2(B,deli) 2/70 (3) 1 0 Slicer 1/103 (1) 1 0 (Cheese, basement) Slicer 0/70 (0) 0 0 (meat, basement ) _________________________________________________________________

1. Transfer of L. monocytogenes to different 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 front Guard back Collection area Blade Guard holder

Hobart Berkel Food Residue Behind the Blade

Product inoculation and slicing
1-cm strip on surface of product inoculated to contain L. monocytogenes at 10 8 CFU/cm 2
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)

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

Slicer blade to product
Product to slicer blade to product

Slicer blade inoculated with a turkey slurry to contain ~10 3 , 10 5 , and 10 8 Lm CFU/blade
Held 1 hour at 21 – 23 ° C before slicing
3 replicates

10 3 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 off  With salami continual transfer likely exceeds 30 slices

Products– turkey, salami, bologna
Surface inoculated to contain 10 5 and 10 8 CFU/cm 2
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 10 3 and 10 5 CFU/blade
Product transfer
Uninoculated product sliced sequentially
24 - 36 replicates

Salami followed by salami
Slice 30
Salami followed by turkey
Slice 10
Turkey followed by salami
Slice 17

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 ~10 8 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

Transfer of Uninjured L. monocytogenes to Salami

Risk Assessment Framework 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 the probability of an adverse effect from a given dose . • Provides a RISK ESTIMATE • What is the nature and likelihood of the health risk? • Who and how many are likely to become ill? • What are the sources of variability and uncertainty in the information used? Jaykus et al. 2007

Contamination Levels at retail (cfu/ g ) Growth in the retail refrigerator Contamination level at consumption (log CFU) / g) Contamination level per serving
Lag time
Growth rate
Storage time
Refrigeration
temperature
Maximum growth
Serving size
Enumeration data
L. 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-over portions
% frequency data
Jaykus et al. 2007

Sl icing 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

Listeria monocytogenes transfer during slicing of delicatessen meats

by dedmark on Sep 23, 2011

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Listeria monocytogenes transfer during slicing of delicatessen meats — Presentation Transcript