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Chapter 2
range of 0.05-0.12 on granite, 0.05-0.22 on marble, 0.05-0.21 on stainless
steel, 0.10-0.41 on white silestone and between 0.01-0.19 on beige
silestone [98]. The SD values were based on four repeated experiments
with three replicates used on each occasion (n=12). The low SD values
reported in the text may indicate the level of stability when using a closed
batch-flow model where each test material is examined separately (no
mixing of nutrients or planktonic cells in contact with multiple surfaces)
[98]. Moreover, the limited number of variables such as flow of nutrients,
shear stress and position within a multi-coupon reactor system (robustness
of method) may have contributed to the low SD values gained in the
research.
Stocki et al. examined biofilm formation of S. Enteritidis and S.
Typhimurium on plastic materials (vinyl, nylon, hemp plastic, farmers belt,
plastic) commonly used for manufacturing conveyor belts in egg processing
facilities [67]. Stocki and colleagues calculated the mean log 10 density of
cells of the five belt types by enumerating the log 10 CFU/cm -2 of cells
recovered from a set of 5 belt pieces stored in 3 petri dishes (n=15 for each
belt type).The surfaces were incubated at 28°C for a total of 14 days to
form a biofilm, consisting of 7 days incubation pre- and 7 days posttreatment
with disinfectant. Despite the repeated measures and extensive
use of replicates, Stocki et al. found large variation in measurement which
was still evident post log transformation of the data. The large variation
between repeated measurements was highlighted through the use of
interquartile range for non parametric data which ranged between 0-2.5
log 10 CFU/1cm 2 depending on material and strain tested [67].
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