View/Open - ARAN - National University of Ireland, Galway

Chapter 3
3.5. Discussion
As illustrated in the SEM images provided in the results (Figure 3.2) the
biofilm was not completely removed from the five surfaces examined (glass,
steel, polycarbonate, tile and concrete). This suggests that the biofilm
formed after 168 hours may be more tightly attached to the surface than
the 48 hour biofilm. As a result the biofilm was more difficult to detach and
recover using the conditions validated previously for the 48 hour biofilm.
The finding of Salmonella biofilm remaining on the surface after sonication
limits the validity of assessing 168 hour biofilm density by enumeration of
recovered cells. However, increasing the duration of sonication or the
intensity of sonication used (kHz) resulted in a reduction in the number of
cells recovered from the surface. Also, as discussed in chapter 2,
alternative options such as confocal microscopy and grid counting were not
possible on all surfaces. Therefore viable plate counting post sonication
remained the most appropriate method for determining the number of
cells remaining on the surface.
A limitation of some published work is that a number of authors have not
provided details on validation of biofilm removal techniques via sonication
[72, 114, 118, 122, 124] including authors removing S. enterica biofilm
formation by other techniques [71, 105, 150]. The use of SEM analysis and
quality control experiments to validate conditions chosen allows
researchers to ensure all limitations relating to the data are apparent.
Hamilton et al. also highlighted the importance of validating biofilm
removal and disaggregation methods. Incorrect reporting of biofilm density
can have major implications, such as an under-estimation of biofilm cells
attached to a surface [183].
Giaouris et al. also confirmed that a 7 day S. Enteritidis biofilm was not
removed from the stainless steel surface via bead vortexing [188]. The
Page
107