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Chapter 5
5. Abstract
Examining biofilm density on food contact surfaces, as described in
Chapters 2 to 4 is time consuming and expensive. Consequently, studies of
this kind are frequently limited to a small number of strains of particular
interest. As a result, a number of lower cost and high throughput methods
for studying biofilm properties have been described. Screening to identify
strains with potential to form a dense biofilm by these high throughput
methods is frequently used as a preliminary step in biofilm studies. In this
chapter, two of these methods are applied to the strains to assess if the
different approaches give comparable or complementary results.
Growth of all strains studied on culture media (congo red agar) indicated
that all strains displayed the red, dry and rough morphology which is said
to be consistent with dense biofilm formers. Using the microtitre plate
assay, the data suggests that S. Agona strains generally formed a more
dense biofilm than S. Typhimurium and S. Enteritidis at room temperature.
However this trend was less apparent when the biofilm was formed at 37°C.
In most instances, the density of biofilm as assessed in the microtitre plate
did not increase over the extended period of time at room temperature.
However, when the biofilm was formed at 37°C for the extended time of
168 hours the mean density increased for 10 of the 13 strains. However,
the large variation in measurements of biofilm density in replicate wells,
even with an individual strain in a single microtitre tray experiment
suggests that caution is needed in drawing conclusions from a limited
number of experiments.
Biofilm formed in the microtitre plate was also treated with disinfectants
sodium hypochlorite, sodium hydroxide and benzalkonium chloride for up
to 90 minutes. The disinfectants were not effective at eliminating all viable
cells from the microtitre plate system. This was broadly consistent with
finding in the CDC biofilm reactor.
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