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Chapter 3
3.4.2. Biofilm density over an extended period of time
Table 3.2 displays the mean log 10 density of cells recovered from the
surfaces after 168 hours biofilm formation. As displayed in Figure 3.2 and
3.3 the 168 hours biofilm was not fully removed from the surface by
sonication therefore the viable counts from the 168 hour biofilm most
likely underestimate the density of biofilm on the surface. Nevertheless in
most instances the mean log 10 density of cells recovered from the surfaces
after 168 hours growth was higher than the mean log 10 density of cells
recovered from the surface when grown for 48 hours. The exceptions were
S. Agona SL483 on steel and polycarbonate (p0.05 on all 3 surfaces).
The largest difference between the number of cells recovered from the
surfaces after 48 and 168 hour biofilm development was seen for the S.
Enteritidis strain S09-0717 (p=0.001 for all 5 surfaces). The mean log 10
density of cells recovered from the surface after S. Agona S09-0494 biofilm
and S. Typhimurium SL1344 biofilm was established also increased after
the extended period of time (p≤0.05 on all 5 surfaces).
The difference in biofilm density after the extended period of time was also
apparent through the use of SEM. As displayed in Figure 3.2, the mean
log 10 density of cells attached to all 5 surfaces after 168 hour biofilm
formation appears more densely populated than after 48 hour biofilm
formation using the S. Agona outbreak strain S09-0494. Moreover the cells
of the 168 hour biofilm structure also appear more tightly attached to each
other than the biofilm formed after 48 hours which indicates that a mature
biofilm may form over the longer period of time.
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