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

Chapter 6
reason for this may be due to only one surface (concrete) contained within
the reactor, which may reduce variability due to mixing of surface
associated properties contained in the enclosed reactor environment.
Alternatively a reason for variation may be due to a less robust
methodology in determining the true extent of variation of mean log 10
density. When mean log 10 density was assessed, as described in chapter 2,
the mean log 10 density was based on 9 observations (counts performed
once on each of 3 coupons x from 3 separate CBR runs) while the method
described in chapter 3 was based on 6 observations (counts performed
once on each of 3 coupons x from 2 separate runs). The results presented
chapter 4 were based on 6 observations (counts performed 3 times on 1
coupon x from each of 2 runs). This change was made to manage the time
available to complete the experiments however it also serves to illustrate
the extent to which the full extent of variability within a single strain may
be underestimated by limitations of methodology. In the latter
experiments because of using fewer coupons the difference in repeated
measures (represented by SD) was smaller. The use of a larger number of
coupons will provide a more comprehensive indication of the ruggedness
of the method and the extent of variation between repeated measures of
the same strain (repeatability). Therefore multiple measurements are
required to confirm apparent differences of biofilm density between
strains examined and differences reported based on less robust methods
may be questionable.
To summarize, the investigation of repeatability of the research performed
on multiple contact surfaces using the CBR, measured by SD values,
appears to correspond with what has been reported elsewhere.
Furthermore the data presented here enhances the understanding of the
density of Salmonella enterica biofilm formation through the use of
Page 207