Preventing Introduction, Growth and

Cross-Contamination of Listeria monocytogenes

©2006 Department of Food Science - College of Agricultural Sciences at Penn State UniversityPenn State is committed to affirmative action, equal opportunity, and the diversity of its workforce.

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Contamination

Introduction– LM is brought into the facility from an

outside source Growth

– LM present in the facility/food has the ability to multiply

Cross-contamination– LM present in the facility/food is

transferred to another food or surface

Introduction of LM

Employees

Rodents/Pests

Customers

Vendors

Contaminated Food

RetailFacility

Non-food items

Retail establishments are open to the public

Restrictions & controls should be designed to complement normal operations

Introduction of LM

Employees– Sources

Ill employees Unclean hands, clothing

– Prevention Good personal hygiene Restriction of ill employees Training

Introduction of LM

Vendors– Sources

Ill vendors Unclean hands or clothing

– Prevention Restriction from high risk areas Training/vendor agreements

Introduction of LM

Customers– Sources

Ill customer

Unclean hands

– Prevention Facilitate proper handing of food

– Tongs, single use paper

– Instructions for proper handing

Introductions of LM

Rodents/Pests– Sources

Feces Rodents/pest carrying LM on feet and body

– Prevention Pest control program Maintenance of indoor and outdoor facilities

Introduction of LM

Contaminated Food– Sources

Raw products (meat, poultry, fruits, vegetable)

Ready-to-eat foods– Prevention

Vendor assurances (HACCP plan, testing) Vendor audits

Introduction of LM

Non-food Items– Sources

Contaminated packaging, other supplies

– Prevention Receiving standards

Growth of LM

Since it is not possible to eliminate all sources of LM in the retail environment, preventing growth is essential– On Food– On Equipment – In the Environment

Controls to Prevent Growth

1. Adequate time and temperature

controls

2. Proper cleaning and sanitation

3. Good personal hygiene

Time/Temperature Controls

Cold Holding (Refrigeration)41ºF for 7 days

OR

45ºF for 4 days

– LM can grow at refrigeration temperatures, so holding time is important

– Control of LM growth is the basis for 2005 Food Code cold holding temperature/time combinations

Growth of Listeria monocytogenes CFA 433 in chicken broth when

incubated at 47.7. 38.3, 34.7, and 33.4oF. Adapted from S.J. Walker et al. (1990).

4

5

6

7

8

9

0 10 20 30 40 50 60

Time (days)

log

10 c

fu/m

l

47.7F

38.3F

34.7F

33.4F

Time/Temperature Control

Date Marking– Requires active managerial control– Applies to:

Certain high risk foods Foods held for greater than 24 hours

– After prepared by a food establishment– After opened, if a processed food

Estimated Reduction of Cases of Listeriosis from Limits on Refrigeration Temperatures

Maximum Refrigerator Temperature

Cases of Listeriosisa

Median

5th Percentile

95th Percentile

Baselineb 2105 ¾c ¾c

7 °C (45 °F) maximum 656 331 761

5 °C (41 °F) maximum 28 1 126

a Values for the median, upper and lower uncertainty levels.b The baseline uses the full empirical distribution of refrigerator temperatures from the Audits International (1999) survey.c The baseline number of cases of listeriosis is fixed based on CDC surveillance data.

Source: FDA/CFSAN and USDA. 2003. Quantitative Assessment of Relative Risk to Public Healthfrom Foodborne Listeria monocytogenes among Selected Categories of Ready-to-Eat Foods

Time/Temperature Controls

Hot holding– Minimum of 135ºF

No temperature control– Can be held for no longer than 4 hours at

ambient temperatures

Cleaning & Sanitation

Prevention of LM growth requires a sanitation program that is:– Properly designed– Properly carried out

Target areas– Food contact equipment at room temperature– Refrigerated storage & display cases

Controls to Prevent Cross-Contamination

Cleaning & Sanitation

Good Personal Hygiene

Proper Flow of Food & Employees

Cleaning & Sanitation

To prevent cross-contamination– Always clean between working with raw

and ready-to-eat products– Regularly clean to reduce chance that

contaminated product transfers to uncontaminated product

Personal Hygiene

Handwashing stations– Easily accessible to

promote frequent handwashing

– Properly supplied Appropriate training

– Employees should understand concept of cross-contamination

Proper Flow of Food

Facility design– Separation of raw and ready-to-eat

areas– Adequate storage and work space

Refrigeration Preparation tables Display cases

Flow of Employees

Facility design– Location of hand washing facilities– Locations of locker & rest rooms– Separation of raw and ready-to-eat

areas Designated tasks for employees Designated work areas

Flow of Employees

Service Area / Cooler

Prep Table Prep Table

Dry Storage Refrigerated Storage

ReceivingRefuse Storage

Dishwashing Area

Locker / Rest Rooms

Handwashing Sink

Coo

ler

Customer Entrance

Employee Entrance

Prevention of LM

Prevent– Introduction–Growth–Cross-contamination