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Chapter 5
5.4. Discussion
The results from assessment of biofilm related properties with the use
congo red agar demonstrated that all 12 S. enterica strains displayed a red,
dry and rough colony morphology. The P. aeruginosa strain 27853
displayed a metallic shine on the surface of the colonies on the CR agar
plate which was different than the S. enterica strains. This morphology was
similar to the rdar morphology displayed by Udea et al. who also
characterised the colony morphology of P. aeruginosa strains [232]. Which
suggests the slight difference in colony morphology is most likely
species/genus related.
The presence of the rdar morphology suggests that the strains synthesized
both curli and cellulose [167]. It has been suggested that these
components may support dense biofilm formation in comparison to strains
lacking curli or cellulose [28, 77, 87, 167]. However, as all the isolates
displaying the rdar morphology, it was not possible to demonstrate an
association between the rdar morphology and increased biofilm density.
The indication that all strains studied form curli and cellulose correlates
with the finding that all strains were able to form a biofilm using the
microtitre plate method and the CBR (chapters 2-4). Previous authors have
suggested that dense biofilm formers can be successfully identified through
examining colony morphology on CR agar [28, 77, 82, 87, 167, 226].
However, other authors have questioned the discriminatory power of this
method suggesting that S. enterica biofilm formation may be more related
to biofilm attachment substrata [67] or the nutrient content provided to
the biofilm [32, 96].
There are also significant limitations to the use of congo red agar to
identify biofilm components. Colony morphology is subject to reader
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