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the surface of the gram-negative bacterium, and
E. coli
is known to have some 10
6
LPS
molecules per cell (Caroff and Karibian, 2006). The interaction of
E. coli
with its immediate
surrounding may to a cetain extent therefore be controlled by these molecules. For instance,
Foppen et al. (2010) found an association between
E. coli
serotype, on one hand, and
attachment efficiency on the other hand. Though the transport mechanisms in the Kampala
aquifers of the strains we used in this work are unknown, the specific serotype O21:H7 may
possibly possess certain characteristics that allow its preferential transport through the
aquifers in the Kampala area, and probably some 60% of the strains possessed this particular
serotype.
According to Garabal et al. (1996),
E. coli
strains belonging to a specific serotype or
serogroup do not themselves confer virulence, rather, it has often been demonstrated that
serotyping can be used as an indicator for pathogenicity, since there is a high positive
correlation between certain serotypes and (entero)pathogenicity. In this work, five serotypes
were identified: O21:H7, O14:H15, O14:H4, O91:H28, O108:H45, and a group with O-
undefinable serotypes. It is interesting to note that all definable O-serogroups were associated
with (diarrheal) diseases: Jenkins et al. (2006) and Kang et al. (2001) reported isolation of
E.
coli
O21 from patients with diarrhea, while Knobl et al. (2001) also identified a pathogenic
E.
coli
isolate of serogroup O21. Furthermore,
E. coli
belonging to O14 and O91 serogroups are
known to be associated with urinary tract infections and diarrhea with life threatening
complications (Stenutz et al., 2006, Bettelheim, 1978). Finally,
E. coli
O108 has been isolated
from faeces of adults with urinary tract infections (Bettelheim, 1978).
7.6 Conclusions
Based on the work from the Kampala springs, the following conclusions can be drawn:
•
Almost all springs we sampled had high concentrations of thermotolerant coliforms,
nitrate and chloride, whereby nitrate and chloride were correlated. This suggested that
waste water, which is so abundantly present and disposed of in Kampala, was the
source of contamination of the springs.
•
Based on column experiments, we concluded that the transport of the
E. coli
strains
was remarkable similar: some 82 % of the strains had a maximum relative
breakthrough concentration between 0.5 and 1, while some 75% of the 40 strains we
tested had similar attachment efficiency values in the order 10
-3
and 10
-4
. We
attributed this to the way in which the strains were harvested: from springs, and
therefore at the termination points of flowlines. Such strains may therefore possess
certain cell characteristics that might have influenced their selective transport in the
subsurface giving rise to their similar transport characteristics in our columns.
•
There was, however, no statistically significant correlation between measured cell
properties (zeta potential, motility, cell size, cell aggregation, and hydrophobicity) and
transport parameters (
f
, Ω
and
k
and (C/C
0
)
max
).
•
The transport of all strains was not only affected by kinetic attachment, but also by
equilibrium sorption. For this, we do not have a good explanation for this equilibrium
sorption phenomenon we observed.
•
Of the strains we tested 58% were of the O21:H7 serotype. This suggests that the
specific serotype O21:H7 may possess certain characteristics that allow its
preferential transport through the aquifers in the Kampala area.
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