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TABLE 2.  Numbers of microorganisms detected in bucket solution after wiping experiments

Organism

L. innocua

E. coli

B. cereus

MS2

Treatment

Positive input control
(mean CFU/PFU ±
standard deviation)

Bucket solution (mean
CFU/PFU ± standard
deviation)

% transferred to and
remaining in bucket
solutiona

PBS
QAC
QAC + soil
PBS
QAC
QAC + soil
PBS
QAC
QAC + soil
PBS
QAC

9.58 ± 0.74
9.60 ± 0.28
8.83 ± 0.37
8.13 ± 0.18
6.33 ± 0.43
5.81 ± 0.20
10.01 ± 0.07
10.06 ± 0.03
9.98 ± 0.03
8.52 ± 1.09
7.80 ± 0.18

9.49 ± 0.99
N/A-LOEb
N/A-LOEb
8.54 ± 0.78
N/A-LOEb
N/A-LOEb
10.54 ± 0.22
9.48 ± 0.19
9.96 ± 0.03
8.39 ± 0.99
N/A-LOEb

99.1
N/A-LOEb
N/A-LOEb
105.0
N/A-LOEb
N/A-LOEb
105.3
94.2
99.8
98.5
N/A-LOEb

QAC + soil

7.46 ± 0.35

6.56 ± 0.38

87.9

Transferred to, and remaining in, the bucket solution was calculated by dividing the number of organisms detected in the bucket
solution by the number of organisms detected in the positive input control and multiplying by 100 [(bucket solution mean/
positive input control mean) × 100].

a

Not applicable (N/A), when the organism was completely inactivated by the disinfectant (limit of enumeration [LOE] reached)
and ratios could not be determined.

b

It is important to note that the results shown in this study
are limited to the organisms included, the use of selective
media (which may prevent recovery of injured cells),
presence of laminated surfaces, the QAC product chosen, and
the use of terry-cloth bar towels. Because we did not account
for injured cells, our results could have underestimated
surviving populations on the surfaces and in the bucket
water, meaning that the number of organisms transferred
from one surface to another, and into the bucket solution,
could have been higher. Future studies using nonselective
medium or increasing the incubation time on selective
medium would be an appropriate next step. In addition, it
was not possible to standardize wiping pressure because of
the large surface area of the surfaces studied. We also did not
measure the concentration of the QAC after it was prepared
(although we did follow manufacturer's instructions) because
we were attempting to simulate a real-life scenario as much as
possible. Front-of-house retail food service employees are not
likely to measure QAC concentration in prepared solutions,
and if they did, there is no record of the accuracy of those
measurements. Although measuring the active ingredient
concentration in studies such as these is not always common,
measuring the QAC concentration, especially after the
addition of soil, would have been interesting, but was

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Food Protection Trends November/December

outside the scope of this study. It has also been shown that
the efficacy of QACs can be reduced by cloth towels (5),
and that effect was not characterized in the current study.
Some common practices also include a cleaning step before
disinfection, and a cleaning step was not characterized here.
Hence, this study only evaluated disinfection, although it
should be noted that the surfaces were very clean, with the
exception of a very small amount of inoculum, at the onset
of the experiments. Further method-development studies to
optimize and standardize wiping actions, such as pressure
on larger surfaces, are warranted, as discussed in Sattar and
Maillard (14), as well as those that investigated the effect of
cleaning a surface before disinfection, and how QACs are
affected by cloth towels in this scaled-up model.
The data for the microbial concentrations in bucket
solutions after wiping are provided in (Table 2). Note that,
when organisms were present and not inactivated by the
QAC, their concentrations were very high and represented
>85% of the initial inoculum enumerated from the positive
control surface. In all cases, high concentrations of the
microbes were detected in the control (PBS) bucket solutions
after wiping. This suggests that the absence of disinfectant use
in cloth and bucket cleaning protocols could result in survival
of vegetative bacteria, viruses, and spores, some of which
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