Food Protection Trends - May/June 2023 - 216

The COVID-19 pandemic has led to mask-wearing in
public and particularly in restaurant and hospitality settings
where there may be close human-to-human interaction.
Educating the public on properly fitting a mask, whether
single-use medical or reusable cloth, has been a challenge, as
well as communicating best practices about mask reusability.
Mask-wearers may frequently adjust the mask to fit properly
over the nose, mouth, and chin when talking or performing
activities. Although there is no evidence to suggest transmission
of SARS-CoV-2 via fomites (hands, surfaces, foods,
etc.), there have been studies to show persistence of the virus
on masks for up to 21 days on inoculated personal protective
equipment when soils were present, which was investigated
specifically to address how long masks could be used before
replacing (13). Because of supply chain shortages, expense,
and implications about waste and pollution, increasing the
time or frequency that a single mask could be worn has
been a significant topic of discussion. However, adjusting
and touching a mask while handling contaminated raw and
ready-to-eat (RTE) foods could lead to transmission of
diseases, such as those caused by foodborne pathogens. Some
information has been provided about how to reuse masks
safely, such as handling the mask by the ear loops or head
straps and storing in paper sacks to allow the mask to dry (for
pathogen die-off), implying that there is an assumption that
used masks are considered contaminated and require careful
handling (3).
During the COVID-19 pandemic, the authors observed
a cooking class in which the chef adjusted their mask while
performing food preparation demonstrations. If foodborne
diseases can be transmitted because of cross-contamination
of utensils or towels, it is possible that a mask could also
serve as a vehicle of foodborne pathogens if not changed
when contaminated. For example, touching a mask while
handling or preparing raw foods followed by touching a mask
while preparing RTE foods could plausibly create a crosscontamination
scenario in which pathogens are transferred
from raw to RTE foods. In an observational study, crosscontamination
occurred up to 43 times in a single meal
preparation activity (16), and current efforts to mask in
public settings and foodservice establishments could increase
the number of or opportunities for cross-contamination if
masks must be adjusted frequently.
The objectives of this project were to evaluate masks as
vehicles of pathogen cross-contamination between food-handling
tasks (slicing contaminated raw chicken and chopping
lettuce) and determine which factors (inoculation level and
slicing time or number of touches), if any, significantly affect
the transfer of bacteria from inoculated chicken to masks and
from contaminated masks to lettuce. To address these objectives,
lab personnel sliced contaminated raw chicken while
touching a medical mask at predetermined time intervals.
The masks were then used as a contamination source while
chopping lettuce by touching the mask at predetermined
216 Food Protection Trends May/June
time intervals. Inoculated chicken, masks, and lettuce were
sampled, and Escherichia coli were enumerated to determine
the log CFU per gram or square centimeter from chicken to
mask and mask to lettuce. The present research highlights
another potential route of cross-contamination during food
preparation. Food safety training professionals, as well as
those who work in laboratory settings, should consider
developing protocols and recommendations for employees
that encourage using disposable masks and changing them
between tasks.
MATERIALS AND METHODS
Design of experiments
To quantify cross-contamination via masks during food
preparation, disposable medical masks were placed on a
mannequin and touched at predetermined time intervals
while slicing inoculated chicken breasts. Touched masks
were then used as the contamination source while chopping
lettuce. All samples were serially diluted and plated onto E.
coli/Coliform (EC/C) Petrifilm (3M, St. Paul, MN). The
project flow is depicted in Fig. 1.
Preparation of nonpathogenic surrogate panel of E. coli
Five E. coli strains (panel MP-26 [ATCC BAA-1427,
BAA-1428, BAA-1429, BAA-1430, and BAA-1431],
Manassas, VA) were maintained at −80°C on protectant
beads (Microbank, Pro-Lab Diagnostics, Ontario, Canada)
in tryptic soy broth (TSB) with glycerol (Difco, BD, Franklin
Lakes, NJ). A single bead for each strain was transferred
into 10 ml of TSB and incubated at 37°C for 24 h for an
overnight culture. For each replication, strains were streaked
individually onto tryptic soy agar (Difco) and incubated at
37°C for 24 h. Single colonies were transferred into 10 ml of
TSB for overnight incubation of 37°C for 24 h. Following
incubation, each strain was centrifuged (9,000 rpm [8,000
× g], 10 min) and washed with 0.1% peptone twice, after
which 5 ml from each strain were combined to create a 25-ml
cocktail (ca. 9.2 ± 0.1 log CFU/ml, counted with a PetroffHauser
counter). From the high-inoculation cocktail, 0.25
ml was used to create a low-inoculation cocktail (ca. 6.8 ± 0.4
log CFU/ml). Each strain in the surrogate panel, as well as
the high- and low-inoculation cocktails, was serially diluted
in 0.1% peptone and plated on EC/C Petrifilm. The panel of
nonpathogenic E. coli was used because it has been shown
to be representative of several Enterobacteriaceae on meat
products.
Preparation and inoculation of chicken breasts with E. coli
Two noninoculated chicken breasts were sampled with a
sponge to ensure no EC/C was detected on the surface (EZReach
polyurethane sponge sampler, World Bioproducts,
Libertyville, IL). Sponges were diluted with 0.1% peptone
and serially diluted before plating on EC/C Petrifilm, which
was used for convenience and efficiency. No EC/C was
Food Protection Trends - May/June 2023

Table of Contents for the Digital Edition of Food Protection Trends - May/June 2023
