Listeria Guidance – Part 1
Sally Hasell
Purpose of Guide 1
1. Gives an overview of the issues – why controls are needed
and why this need is becoming greater than ever
2. Identifies how Listeria gets into food via the environment,
contaminated surfaces, ingredients and equipment
3. Explains why there must be a focus on RTE foods that
support the growth of Listeria
4. Discusses microbiological limits and how they are applied
5. Describes how to setup, document and implement a
Listeria Management Programme
What makes Listeria special?
1. Grows at low temperatures i.e. during refrigerated storage
of food and in chillers
2. Grows in most types of packaging – vacuum packing does
not inhibit it
3. Is everywhere in the environment, so can potentially be reintroduced into clean areas at any time
4. Is able to invade the cells of people with poor immune
systems and cause very severe often fatal illness
Why Listeria needs to be controlled
1. Cases are few (20 a year) but high mortality rate (25%)
and includes babies
2. If a large quantity of highly contaminated food got into the
market, many could be hospitalised and die
3. Vulnerable consumers such as the elderly and those with
poor immune systems are an increasing group
4. Food preferences are increasing the volume and types of
RTE foods that Listeria can survive and grow in
Listeria sp.
•Only Listeria monocytogenes is a significant human pathogen
•Other members e.g. L.innocua are rarely harmful but share
other characteristics with L.monocytogenes
•This means finding any type of Listeria in food or somewhere
it should not be, means that control is needed or has failed
Growth in food as a critical factor
•Small numbers of Listeria are unlikely to be a problem for healthy adults
but as numbers increase, the potential for illness increases
•When number get really high, even healthy adults can become ill.
If Listeria can grow in a food, over time a small number can quickly
become a large number, especially if temperature control not good
HIGHEST RISK FOOD ARE THOSE THAT SUPPORT THE GROWTH
OF LISTERIA AND ARE STORED CHILLED FOR MORE THAN 3 DAYS
Control strategies
• Listeria present are destroyed or removed - apply a
listericidal step, wash, incoming ingredient specs
•Limit the potential for growth in the food e.g. low pH (<4.4),
water activity <0.92, combinations of pH and water activity and
other hurdles, freeze, some packaging
•Prevent/protect from recontamination, especially after a
listericidal step
Preventing recontamination
A major problem is when food gets contaminated after a
listericidal step e.g. cook the ham and then slice and package
Need to make sure that cannot get contaminated – slicers,
conveyor belts, aerosols, condensation drips, work flow, people
Focus cleaning and sanitation on this part of the process i.e
create a high care hygiene area and monitor effectiveness
How many is too many?
•Healthy consumers can tolerate small numbers of Listeria in
their food but vulnerable consumers may not.
•Thus important that Listeria should not be detected in food
intended for these consumers e.g. infants.
•Foods that are consumed regularly by all consumers should
also be Listeria free e.g. spreads, butter, milk
• Foods like salads need to make sure fresh and washed to
keep numbers as low as possible
How many Listeria is too many?
Food should never have more than 100cfu/g of Listeria
monocytogenes present.
When counts are >100cfu/g it is obvious that Listeria controls
have failed •Incoming ingredients
•Processing control steps failed
•Contamination from equipment, environment
Listeria limits and Regulators
•Zero limits typically set to support strategies to reduce the
incidence of listeriosis and for foods known to be problematic
Std 1.6.1 for example
•Now international agreement that the focus is on not letting
numbers get above 100cfu/g and this most often is because of
contamination during processing and then growth during chilled
storage
Microbiological targets
Product Characteristics of the food and
risk
processing
group
L. monocytogenes level targets
At the end of
processing
At the end of
shelf life
High
Absent in 25g
Absent in 25g
Medium Processed RTE foods in which
growth will not occur
Absent in 25g
Not more than
100cfu/g
Low
L. monocytogenes
not a pathogen of
concern
Testing not usually
required. Not
more than
100cfu/g
Processed RTE foods in which
growth can occur (during storage in
final packaging) and the food stored
refrigerated for > 3 days
Products where the occurrence
and/or survival is highly unlikely
Microbiological limits
Regulatory limits that may apply to a product
•Food Standards Code Std 1.6.1
•Product safety limits for dairy products (DPC1)
•Operator defined limits
•Customers
•Countries to which exporting food
Listeria Management Programmes
A record of how a business manages Listeria • What controls are in place e.g. specifications, cleaning/
sanitation, training, monitoring, responding to failures, new
products and processes reviewed
•How they are done e.g. new staff get trained, pasteurisation
failures responded to, out of spec ingredients rejected, lab
results acted on, new equipment checked
Listeria Management Programmes
Provides an overview of the Listeria control system so that
everyone (management, auditor, regulator, customer) knows
what is being done, their role and how to see and know when
it is failing
Critical aspects of a LMP
•It is written down
•Everyone who needs to be involved is
•It truly reflects what is happening in the processing
environment
•Observations made are responded to
•It is a living document
•It is focussed on the key factors that could be the source of
contamination