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Chapter 6
glass, 0.18-0.94 on steel, 0.17-0.70 on polycarbonate, 0.05-0.68 on
concrete and 0.08-0.28 on tile (figures based on results presented in
chapter 2, Tables 2.3-2.5). The SD varied between the 13 strains and there
appeared to be no pattern of larger or smaller SD values for any particular
strain or serovar.
As described in chapter 2, the previous research performed using the CBR
[72, 117, 124] suggests that the repeatability, when measured using the SD,
is similar to what has been achieved in this thesis. However, in most
instances the research to date has examined a limited number of replicate
surfaces or repeated experiments. It is also evident that the large number
of strains tested in this thesis and the 5 surfaces examined simultaneously
allow for the most comprehensive investigation to date of the density of
Salmonella biofilm formation on multiple surfaces and of the variance of
repeated measures using the CBR.
Joseph et al. investigated the biofilm density of 3 S. enterica serovars on
concrete, plastic and steel but did not report the SD of the duplicated
experiment [71]. Nevertheless the work performed by Joseph et al. is
widely used as a reference to demonstrate biofilm formation on contact
surfaces and resistance to sanitizers. The repeatability of measurements
when examining the efficacy of the disinfectant against a pre-established
biofilm in this study was similar also to that reported elsewhere [117, 134,
150].
Interestingly, the SD values were much lower when assessing log 10
reduction of viable cells attached to concrete post treatment (details in
chapter 4) than when assessing mean log 10 density on 5 surfaces
simultaneously, as described in chapter 2 and chapter 3. It is possible that a
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