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Chapter 2
2.6.5. Mean log 10 density of S. Agona biofilm cells
Table 2.3 presents the mean log 10 density (CFU/coupon) of S. Agona cells
attached to glass, stainless steel, polycarbonate, concrete and glazed tile.
Table 2.3 also provides an indication of the level of intra-laboratory
reproducibility through the use of the standard deviation (SD). The results
suggest that S. Agona S09-0371 formed a more dense biofilm than all other
S. Agona strains. The sequenced S. Agona reference strain SL483 also
formed a dense biofilm on glass, stainless steel and polycarbonate but
formed a less dense biofilm than all other strains on concrete and tile.
Based on the results presented in Table 2.3 the S. Agona strains associated
with the outbreak (S08-0601 and S09-0494) do not appear to be more
dense biofilm formers than any of the other S. Agona strains examined and
if anything form a less dense biofilm compared with S09-0371.
Possible differences between the biofilm density for the S. Agona strains
was further evaluated. Table 2.3 displays the difference in mean log 10
density of biofilm produced by the S. Agona strains by subtracting the
mean log 10 density values for the respective strains from each other. The
results provided in Table 2.3 indicate that there were only minor
differences at best between all strains with PFGE type SAGOXB.0066. As a
result the S. Agona strain S08-0601 was used as representative of this PFGE
type for further comparisons. Based on the results presented in Table 2.3
there appears to be little difference between the S. Agona PFGE type
SAGOXB.0066 (S08-0601) and the S. Agona variant strain (S09-0046 –
differs by 2 band based on PFGE analysis) with p>0.05 on all 5 surfaces. In
relation to comparisons with strains entirely unrelated to the outbreak
there was a tendency for the S. Agona SAGOXB.0066 related strains to
form a less dense biofilm than the other strains tested.
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