Food Protection Trends - January/February 2023 - 34

For instance, a facility identifying a pathogen, such as
Listeria monocytogenes, as a potential hazard in ready-to-eat
food must implement sanitation preventive controls. Efficacy
of cleaning and sanitizing protocols (sanitation) requires a
verification process, such as an environmental monitoring
program (4, 24). There are several environmental monitoring
program methods and tools to assist facilities in verifying
if sanitation protocols are effective, including an in-house
or third-party laboratory to perform microbial swabbing
for aerobic plate counts, yeasts, molds, Enterobacteriaceae,
Escherichia coli, and Listeria species (or specifically targeting
the pathogen L. monocytogenes). In addition, rapid methods
and tools may also be used as means to verify sanitation,
such as the detection of ATP, allergens, and protein and
carbohydrate residues.
Specifically, ATP is a molecule that drives cellular function
and is found in all biological materials, including cell-containing
food matter. Rapid quantification of ATP is possible
by using a bioluminescence assay. This assay consists of the
consumption of ATP in a reaction between luciferin and
luciferase, which produces a fluorescent light (9). The light
intensity from this reaction can be quantified by using an
ATP luminometer, which estimates ATP in relative light
units (RLU) (5). RLU levels are readily displayed on the
luminometer in as little as 15 s, providing efficient and rapid
results. RLU levels above facility-set thresholds indicate that
a surface may not have been adequately cleaned, as biological
material is still present on the surface. These set thresholds
may vary between the type of food facility, type of surface,
and cleaning and sanitizing protocols. For these reasons, it
can be challenging to extrapolate ATP data across food facilities,
especially in terms of microbial risk.
Given the relative convenience, cost efficiency, quick
results, and usefulness in evaluating the cleanliness of surfaces,
it is not surprising that ATP assays are frequently used
in food facilities, despite disparate evidence regarding the
ability to predict the presence of microbial hazards (14, 18,
20, 21). A laboratory-based surface study performed by Lane
et al. (18) concluded that although ATP bioluminescence
could be used to measure Listeria innocua on stainless steel
and high-density polyethylene coupons, it was unreliable on
wood surface coupons. ATP bioluminescence was also compared
against aerobic plate counts to evaluate the sanitation
of cutting boards (20). Both ATP and aerobic plate counts
were comparable when evaluating the sanitation efficacy on
cutting boards with bacterial inocula (20). In a preoperational
survey of 30 retail delis, Hammons et al. (14) found a
fourfold increase in the likelihood of detecting L. monocytogenes
when ATP measurements increased by 1 log RLU on
corresponding surfaces. Conversely, a different study found
no statistical difference in ATP RLU levels between Listeria
spp.-positive and-negative food contact surfaces in five commercial
apple packinghouses (21). Therefore, the usefulness
of ATP is goal specific, as data describing ATP as an indicator
34
Food Protection Trends January/February
of microorganisms vary on the basis of facility, surface, and
process, among other factors (1). In addition, the use of ATP
is facilitated by an understanding of a cleanliness baseline
before and after cleaning activities.
An under-investigated area along the food supply chain
is at the transportation and distribution center level (often
described as the area between packing and processing and
retail) (30). Distribution centers fall under the Preventive
Controls for Human Food Rule, as they hold human food for
consumption and thus must develop and implement a riskbased
food safety plan. Although limited data on microbial
hazards in this environment exist, there is concern regarding
the possible introduction of environmental pathogens to
products in distribution centers (31). Many areas within
distribution centers are held at refrigeration temperatures to
maintain food quality and safety during storage, and prior
research has shown Listeria survival and persistence in these
temperatures and environments (7, 29, 31). To generate data
in this environment and address this concern, a microbial
survey was conducted in 17 food distribution centers to
quantify Listeria spp. on non-food-contact surfaces. In
addition, other attribute data (e.g., ATP, sanitation protocol
frequency) were collected to investigate associations with
Listeria (31). This study used Listeria spp. as an index
organism for L. monocytogenes due to the sensitive nature of
detecting an L. monocytogenes-positive sample in an active
food distribution center (8). The objective of this study was
to determine if ATP bioluminescence levels were associated
with Listeria spp., as these data were collected concurrently
from environmental surfaces.
MATERIALS AND METHODS
Microbiological sampling
Seventeen distribution centers handling fresh produce
were visited once between December 2019 and March
2021. These distribution centers represented two firms
selected from a convenience sample of firms identified with
assistance from the funding organization (31). These centers
handle items other than produce, such as meat, poultry,
and nonconsumables. Approximately 18 environmental
surface samples were collected per facility (n = 300) by
using Sponge-Sticks with 10 ml of Dey-Engley neutralizing
broth (3M, St. Paul, MN). Sample sites were chosen on the
basis of the facility design, size, and general location (e.g.,
shipping and receiving docks, cold storage) to distribute
samples collected throughout the facility. Only non-foodcontact
surfaces were sampled, such as floors, pallets,
shelving, and equipment, using 30 by 30 cm areas. Foods
and food contact surfaces (e.g., packaging) were not sampled
as requested by the participating firms. However, non-foodcontact
surfaces serve as harborage sites, which can lead to
cross contamination on food-contact surfaces. Samples were
coded to blind the laboratory to collection site locations
prior to microbiological analysis. After sampling, sponges
Food Protection Trends - January/February 2023

Table of Contents for the Digital Edition of Food Protection Trends - January/February 2023
