Food Protection Trends - September/October 2022 - 392

The advantage of collector samples is that a relatively few
samples can give an indication of the likely presence of Listeria
in a processing area. The disadvantage of collector samples is
that they do not reflect the source of the Listeria found. For
example, Listeria present on an operative's footwear could have
originated anywhere that the operative has walked since the
footwear was last cleaned.
For all sample points, a direct action plan should be detailed if
a Listeria positive is detected. These could include the following:
* For Listeria found at barrier sampling points, review the
barrier performance. For example, if Listeria is found at
the exit of a disinfectant spray tunnel, review whether
the disinfectant concentration is correct, whether the
speed of the tunnel conveyor is unchanged, whether all
spray nozzles are present and working, whether products
are placed on the conveyor correctly (i.e., the previously
noted monitoring parameters).
* For Listeria found on known sources and vectors, review
source and vector controls and frequencies. For example,
if L. monocytogenes is found on the surface of a floor crack,
which is known to harbor L. monocytogenes and which is
controlled by disinfecting the floor every 8 h, increase the
disinfection frequency to every 6 h.
For Listeria found on collectors, establish the following:
◊ Where has the Listeria come from?
◊ Where could it be spread to via environmental or
product vectors?
* For Listeria found on food processing equipment posthygiene,
review the cleaning and disinfection program. Has
the cleaning program generically failed, e.g., are there
accompanying high ATP, total viable count, or Enterobacteriaceae
levels? Or was it working correctly but unable
to control Listeria? If the cleaning program performance
was ostensibly acceptable, the cleaning program could be
further improved by additional energy inputs from chemicals,
temperature, or mechanical action, or by additional
dismantling of the equipment prior to cleaning.
For Listeria found on collectors (probably the most likely
indicator of Listeria presence in the environment), what is the
Listeria strain?
* Is it a random strain that might be indicative of sporadic
isolation? This may be a temporary or transient strain that
would be removed with cleaning and disinfection.
* Is it a recurring strain that may be indicative of strain persistence?
This may indicate an unknown or uncontrolled
Listeria source within the manufacturing infrastructure.
All sample points, their purpose, and the actions that should
be taken if they test positive should be described in a sampling
plan. In addition, the position of all sampling points should be
detailed on a map of the food processing area.
Environmental sampling journey
Many factory environmental sampling plans have been built
up over a number of years and have been influenced by staff
392 Food Protection Trends September/October
changes, product and process changes, customer (retailer)
requirements, and legislation. Their original purpose may
have been lost, and they may essentially be random in nature
with no clear purpose. The adoption of a new environmental
sampling plan, such as to facilitate the Listeria 5-point system,
is really a sampling journey and consists of four stages (Fig. 4):
Stage 1: Adoption of a pathogen management system
such as the 5-point system outlined above. Many existing
environmental sampling plans have aspects of source and
vector identification, collector, and posthygiene samples. The
source, vector, and collector samples are usually not structured,
and there may be a preponderance of samples from after
cleaning and disinfection (posthygiene).
Cleaning procedures used to control Listeria are part of a
defined prerequisite plan to control the risk of a specific hazard,
and GMPs and EU legislation require that the cleaning and
disinfection procedures and their frequency thus need to be
validated, monitored, and verified. This is also a requirement
of the Global Food Safety Initiative endorsed audit standards,
such as the British Retail Consortium Global Standard
for Food Safety version 8, which specifically mentions the
need for verification after cleaning and disinfection (3). The
presence of this requirement in auditing standards leads to
perhaps excessive posthygiene sample numbers. In addition,
there is usually a wealth of monitoring evidence concerning
the success of the cleaning operation (visual assessment,
ATP or other rapid method assessment of cleanliness prior to
disinfection, operative and supervisor check-off sheets) that
should diminish the need for verification samples.
The major omission in many existing sampling plans is
barrier samples. In stage 1, therefore, barrier samples are
usually added, posthygiene samples reduced, and collector
samples refocused.
Stage 2: " Seek and destroy. " The term " seek and destroy "
was first coined by Dr. John Butts in the United States and is
described in Malley et al. (18). The prime purpose of stage 2
is to identify potential sources and vectors of Listeria with the
aim of eliminating or controlling them. This process can take a
long time and involve hundreds of samples. There are three key
factors involved:
* A formal assessment of the high hygiene area for likely
sources and vectors by the site PEP team (step 8 of the
PEP). This should be undertaken during all types of
processing conditions, such as production, cleaning
windows, downtime, and maintenance work.
* Assessment of the risk of each source or vector. For a
source, this is based on the likely presence of Listeria at
the source and its ability to spread from the source; for
a vector, it is based on the likely presence of Listeria at
the vector and the vector frequency. The determination
of Listeria on the potential sources and vectors with the
highest risk should be established first.
* It is very unlikely that Listeria will always be present in
samples taken from a source or vector, even though it
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