Food Protection Trends - November/December 2020 - 396

TABLE 1. Cross-contamination efficiency ratios of microorganisms from an inoculated
laminate surface to a clean laminate surface with a single wiping step using the
cloth and bucket method
Organism

L. innocua

E. coli

B. cereus

MS2

Treatment

CFU/PFU on surface 1-
dirty (mean ± standard
deviation)

CFU/PFU on surface 1-
clean (mean ± standard
deviation)

Cross-contamination
efficiency (mean ± standard
deviation)a

PBS
QAC
QAC + 5% soil
PBS
QAC
QAC + 5% soil
PBS
QAC
QAC + 5% soil
PBS
QAC

7.24 ± 0.99
3.77 ± 0.27
4.18 ± 0.29
5.26 ± 1.26
3.19 ± 0.42
3.72 ± 0.30
8.85 ± 0.06
9.04 ± 0.34
9.13 ± 0.16
6.34 ± 0.96
5.51 ± 0.94

6.79 ± 0.88
LOEb
3.51 ± 0.38
5.08 ± 1.29
LOEb
3.01 ± 0.40
8.75 ± 0.08
8.90 ± 0.22
9.20 ± 0.07
5.80 ± 0.86
4.41 ± 0.78

1.08 ± 0.06
N/Ab
1.20 ± 0.05
1.05 ± 0.05
N/Ab
1.28 ± 0.17
1.01 ± 0.01
1.01 ± 0.02
0.99 ± 0.02
1.09 ± 0.03
1.26 ± 0.17

QAC + 5% soil

5.50 ± 0.88

4.76 ± 0.22

1.15 ± 0.18

Cross-contamination efficiency was calculated as a ratio of the total number of organisms on the inoculated side of S1d to the total
number of organisms on S1c after the first wiping event (S1d/S1c).

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

terry-cloth bar cloth was dunked in a solution and used to
wipe the contaminated area in a back and forth motion to the
clean side of the surface (S1c). By determining the number
of microorganisms remaining on S1d, and the number that
were moved to S1c by the cloth during wiping, we were able
to determine the efficiency of cross-contamination from the
initial contamination source to a clean surface, also known as
the initial cross-contamination event (Table 1). The efficiency
of cross-contamination was calculated as a ratio of the number
of organisms enumerated from S1d to the number of organisms enumerated from S1c. A result close to 1.0 indicated that
close to an equal number of the test organisms were found on
both the inoculated and the cross-contaminated sides of S1
after wiping and that the organism was easily moved from one
side of the surface to the other. Cross-contamination efficiency
ranged from 0.99 to 1.28, showing the test organisms were
moved efficiently from the inoculated side of S1 (S1d) to the
clean side of S1 (S1c). In some cases, this occurred even when
the disinfectant was used, with or without soil. This shows that
the initial wiping of a contaminated surface using the traditional cloth and bucket method easily spreads organisms to clean
areas of the same surface.
The efficacy of disinfection was dependent upon microorganism, bucket solution type, and sequence of wiping

396

Food Protection Trends November/December

actions. These data are provided in Figs. 2 through Figs. 5
as log PFU or CFU transferred to a surface for each of the
sequential wiping actions. For E. coli and L. innocua, when
the bucket contained PBS alone (control), cross-contamination occurred with each sequential wiping step, although its
efficiency reduced with subsequent wiping events (Figs. 2 and
3). By the fourth wiping event, about 5-log less CFU were
deposited on the clean recipient surface. Further, cross-contamination appeared less efficient if first preceded by rinsing
the cloth in the bucket solution (as was the case for S1 vs. S2
and S3 vs. S4) as compared to two sequential wipes without a
cloth rinse (S2 versus S3).
When the bucket contained the QAC solution, with or
without added soil, the disinfectant quickly inactivated
both L. innocua and E. coli and effectively prevented crosscontamination, which was negligible after the first wipe
(S1c) and below assay enumeration limits (< 2.78 log CFU/
surface) for S2, S3, and S4.
Overall, these results were expected because it is readily
accepted that quaternary ammonium compounds are
effective in inactivating vegetative gram-positive and gramnegative bacteria (6). These data are consistent with the study
of Scott and Bloomfield (15), in which two different types
of cloths were evaluated for cleaning in a food-preparation

Food Protection Trends - November/December 2020

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