Page 117 - Journal of Special Operations Medicine - Summer 2016

distilled water and inoculated with approximately Figure 2 Number of water reservoirs containing E. coli and
500 million bacterial cells, or CFUs. Two reservoirs other biological contaminants following cleaning treatment.
were used as controls: a positive control that was in- Both bleach and the CamelBak cleaning tablet are effective at
oculated but not cleaned and a negative control that reducing the numbers of total bacteria (expressed as CFUs) after
was filled with distilled water but not inoculated. All treatment. The blue bar indicates reservoirs from which 1 CFU
were incubated for a total of 4 weeks at ambient tem- was detected. The maroon bar indicates reservoirs from which
more than 1 CFU was detected.
perature in an open-air outdoor shed. Water samples
from the reservoirs were collected and plated for
bacterial growth before and after cleaning with the
bleach, baking soda, and a proprietary CAMELBAK
Cleaning Tab.

After 4 weeks of incubation, it was found that all sam-
ples had significant contamination before any cleaning
treatment. Organisms other than E. coli were noticed
and determined by visual inspection. All the plates had
too many colonies to count after 24 hours, and there
was no significant difference in bacterial growth among
the three treatment groups. Discussion
One interesting result of this study was the fact that ster-
After treatment, it is significant to note that the proprie- ile distilled water allowed E. coli to survive for at least
tary cleaning tablet was most effective at removing all E. 4 weeks in the water reservoir while Honolulu County
coli with no organisms remaining in the posttreatment municipal city water did not. Our initial hypothesis was
water samples (Figure 1). Bleach was also effective at that the bacteria would survive longer in municipal city
removing E. coli. Seventeen of the 20 reservoirs (85%) water due to the greater abundance of dissolved solutes
had no E. coli after the bleach treatment. In addition, and micronutrients. This result may be explained by
both of these treatment methods were also effective at the fact that city water is often treated with chlorine,
reducing total bacterial levels (E. coli and other contam- which is known to inhibit bacterial growth. A subse-
9
inating organisms) (Figure 2). quent search of the literature revealed that certain bacte-
rial species may be able to survive for up to 16 years in
pure distilled water. 10,11 Based on these results, it is not
However, baking soda was the least effective in clean-
ing, with at least 70% of the samples having at least advisable to clean a water hydration system by merely
one organism posttreatment. The proprietary tablet and washing it with distilled water, as distilled water is not
bleach did significantly better than baking soda (P < antibacterial and may favor the survival of certain bac-
.001 based on a Fisher’s exact test). There were no teria. It is also not advisable to fill a hydration system
significant differences between the cleaning tablet and reservoir with distilled water and let it sit for any period
bleach (P = .231 based on Fisher’s exact test). of time as this may allow the accumulation of environ-
mental bacteria. Chlorinated water appears to be the
best choice for use with these systems for its antibacte-
Figure 1 Number of water reservoirs containing E. coli rial property.
after cleaning treatments. Both bleach and the CamelBak
cleaning tablet are effective at reducing the numbers of E. coli It was also interesting to note that bleach and the pro-
(expressed as colony forming units [CFUs]) after treatment. prietary cleaning tablet manufactured by CamelBak
The blue bar represents reservoirs that had at least one were the most effective cleaning agents. Both com-
organism post-treatment and the maroon bar represents pounds tend to kill bacteria by the release of chlorine
reservoirs that had more than one organism post-treatment.
into solution, which acts to block cellular metabo-
lism. 12,13 As there was no statistically significant dif-
ference between the two, it can be assumed that they
were both capable of delivering bactericidal chlori-
nated compounds into the bacterial cell. Although
baking soda has been reported to have some antibac-
terial activity, it appears to be more effective when
combined with sodium dodecyl sulfate. The lack of
that compound in the baking soda used in this study
may have contributed to its failure in adequately
cleaning the water reservoirs. 14

Cleaning Methodologies for E. coli Isolate 103