Food Protection Trends - November/December 2020 - 399

area. They observed high aerobic plate counts for both
cleaning cloths and on the associated surfaces after cleaning
in the absence of a disinfectant. What was interesting in the
current study was that the efficacy of the disinfectant was
maintained even in the presence of a relatively high soil load,
despite suggestions that a higher concentration of QAC is
needed to be efficacious in the presence of high soil (5).
Medrano-Félix et al. (10) demonstrated that households in
which a QAC disinfectant intervention was introduced had
reduced numbers of E. coli on kitchen countertops over time,
compared with households that did not receive the QAC
intervention, which showed no change or increased numbers
of E. coli on countertops. Our work also demonstrates the
efficacy of QAC disinfectants against representative gramnegative and gram-positive bacteria, even in the presence of a
significant organic load.
The results for bacteriophage MS2 are shown in Fig. 4. The
results for the positive control (PBS as bucket solution, no
disinfectant) showed that quantifiable cross-contamination
occurred through wiping of S3. With the first wipe, approximately 2.5 log PFU/surface was removed and/or inactivated,
giving a concentration of 6.1 ± 0.9 log PFU on S1. After submerging the cloth in PBS and using that cloth to wipe down
S2, 3.7 ± 0.9 log PFU was transferred, with 3.0 ± 0.3 log
PFU/surface then transferred to S3, representing subsequent
cross-contamination. After submerging the cloth in PBS for
a second time, the MS2 was not detected on S4 after the last
wiping event, at least within the enumeration limit of the
assay (which was < 2.78 log PFU/surface).
The data for QAC, with and without added soil, were
similar but not identical to that for PBS. In the absence
of added soil, MS2 became undetectable on S2, showing
some benefit of the QAC in preventing long-term crosscontamination. For QAC with 5% soil experiments,
cross-contamination was never completely ameliorated
since quantifiable virus was present even on S4, albeit
the concentrations of MS2 for S3 and S4 were low, at 3.6
± 0.1 log PFU/surface and 3.4 ± 0.3 log10 PFU/surface,
respectively. For all three treatments, rapid inactivation and/
or removal of virus occurred between the positive control
and S2; thereafter, inactivation or cross-contamination was
either marginal or nonexistent (because the assay limit of
enumeration had been reached).
MS2 was chosen for use as a surrogate for human enteric
viruses, specifically HNV. It has been shown that HNV has
long-term persistence (weeks) on surfaces, and in general,
QACs have poor efficacy against HNV (19). The results of
this study were somewhat surprising if taken in the context
of MS2 being used to model HNV behavior. The fact that
so much of the virus was lost between the positive control
and S2, whether or not the disinfectant was present, suggests
that MS2 was effectively removed by the act of wiping. There
is little information on the efficacy of rubbing to remove
HNV, with one study showing approximately 1 log removal

of HNV depending on the type of cloth used (8). In the
same study, the impact of cloth type on the transferability of
HNV surrogates (MS2 and PRD1 bacteriophages and feline
calicivirus) to stainless steel surfaces was evaluated and found
to be cloth dependent, ranging from very little transferred to
around 3 log PFU. Hence, we should be cautious in assuming
that HNV would be removed by cloth wiping because there
are many variables in our study that were not evaluated.
Unfortunately, because removal appeared to be so effective,
there was only a small window (about 1 log PFU) in which
to evaluate efficacy of the QAC, not enough to make any
compelling conclusions about sanitizer efficacy. In short,
further studies are required to truly understand the behavior
of HNV with respect to cross-contamination and inactivation
in reusable cloth-and-bucket scenarios.
Results for wiping experiments with B. cereus differed
quite considerably from those for the vegetative bacteria and
MS2. In the absence of a disinfectant (PBS control), 8.8 ±
0.1 log CFU/surface remained on S1 after the first wiping
step, suggesting that approximately 1.2 log CFU/surface
was removed by the act of wiping when compared with the
positive control. After submerging the cloth in PBS and then
using that cloth to wipe down S2, a total of 7.0 ± 0.4 log CFU/
surface was transferred. This degree of cross-contamination
remained relatively consistent for subsequent wiping steps
(S3 and S4). When QAC without added soil was used as the
bucket solution, very similar results were observed, strongly
suggesting that the QAC had no sporicidal effect on B. cereus.
This was not unexpected because the efficacy of QACs on
spores has been shown to be formulation dependent (6). The
addition of 5% soil to the disinfectant solution had something
of a protective effect in wiping experiments, with only 0.8 log
CFU/surface removed in the first wiping action and relatively
consistent cross-contamination (8.4 ± 0.1 log CFU/surface,
8.3 ± 0.1 log CFU/surface, and 7.8 ± 0.1 log CFU/surface for
S2, S3, and S4, respectively) occurring thereafter.
Collectively, B. cereus spores were readily transferred from
surface to surface, regardless of the solution used for wiping
experiments. The spores were resistant to inactivation by the
QAC and may have been protected by the addition of soil. As
was the case for the vegetative bacteria, cross-contamination
appeared less efficient if first preceded by rinsing the cloth
in the bucket water (as was the case for S1 versus S2 and S3
versus S4) as compared with two sequential wipes without a
cloth rinse (S2 versus S3). These data clearly demonstrate the
environmental resilience of spores and their ease of spread
from surface to surface using reusable cloths, regardless
of whether or not a QAC disinfectant is present. This was
perhaps expected because some studies of disinfection of C.
difficile spores have found that QAC-based disinfectants did
not have sporicidal properties (7). The results of this study
support those of previous ones (18) showing that C. difficile
spores are easily transferred by reusable cloths to surfaces
across multiple wiping events.

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