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Chapter 3
Table 3.2: Difference between the 48 hour and the 168 hour biofilm (measured in Mean Log 10 CFU/coupon)
Strain Glass Steel Polycarbonate Concrete Tile
N 168H 48H Diff P 168H 48H Diff P 168H 48H Diff P 168H 48H Diff P 168 48H Diff P
†
†
†
†
H
†
S09-0494 6/9 7.26 5.41 1.85 0.001 6.92 5.80 1.11 0.001 6.67 6.33 0.33 0.011 7.59 7.08 0.51 0.001 7.87 7.56 0.31 0.018
SL483 6/9 5.91 5.81 0.10 0.553 5.29 6.12 -0.84 0.007 5.46 5.59 -0.13 0.003 7.08 6.75 0.34 0.033 7.52 6.94 0.58 0.001
S09-0419 6/9 6.30 5.41 0.89 0.001 6.00 6.28 -0.28 0.087 6.25 6.53 -0.28 0.260 6.93 7.00 -0.06 0.906 7.73 7.23 0.49 0.001
SL1344 6/9 5.97 5.15 0.83 0.015 6.59 5.71 0.87 0.001 6.30 6.10 0.20 0.050 7.47 6.78 0.69 0.001 7.62 7.17 0.44 0.001
S09-0717 6/9 6.73 4.85 1.88 0.001 6.87 4.73 2.14 0.001 6.80 5.20 1.61 0.001 7.65 6.43 1.21 0.001 8.04 7.02 1.02 0.001
Table 3.2 displays the mean log 10 density of cells recovered from the surfaces after 48 and 168 hour biofilm formation. The strains examined
included 2 Salmonella enterica subspecies enterica serovar Agona strains (S09-0494 and SL483), 2 S. Typhimurium strains (S09-0419 and
SL1344) and 1 S. Enteritidis strain (S09-0717). The difference between the density of cells recovered after the 48 and 168 hours is also
displayed through the use of mean difference (Diff= mean density at 168hours –mean density at 48 hours) and p values. † Any comparison of
the two methods (48 hour and 168 hour biofilm development) needs to be made with a great degree of caution as the 148 hour biofilm was
not fully removed from the surface (See SEM images Figure 3.2 and 3.3 for illustration of biofilm remaining on surface). However in most
instances the mean log density of cells recovered from the surfaces after 168 hours growth was still higher than the mean log 10 density of cells
recovered from the surface when grown for 48 hours.
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