View/Open - ARAN - National University of Ireland, Galway

Chapter 6
attributable to a small number of outlying high values for these strains
which impacted significantly on the mean OD. If those outlying values were
not considered the evidence of difference is much less. As discussed in
chapter 5, the observation that S. enterica biofilm density does not
increase over time using a microtitre plate method has also been reported
elsewhere [56, 149, 165]. Previous authors have also suggested that the
use of microtitre plate systems may have limitations due to a limited
surface area indicating that bacteria may reach a saturation level where
the volume of attached cells peaks over time depending on conditions [165,
191]. The small surface area of biofilm substratum may also not reflect
conditions in food processing areas where the surface areas may be much
larger and open to nutrient flow and contact with contaminants. However,
this may be a limitation to all laboratory based biofilm development
models as it may not be possible to replicate all biofilm development
conditions found in food processing areas.
6.5. Overall comparison of biofilm development in CBR and
microtitre plate
When the strains were assessed for biofilm development using the CBR in
most instances the density of biofilm formed by S. Agona strains was
greater than the biofilm formed by S. Enteritidis strains over 48 hours at
22°C. This broadly corresponds with what was reported using the
microtitre plate based method for 48 hours (based on the mean density of
the strains). However the results were less consistent using the microtitre
plate method.
However, in many instances the results of the 168 hour biofilm formed
using the CBR did not correlate with the findings of the microtitre plate
method after 168 hours. The S. Enteritidis strain S09-0717 was a dense
Page 201