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Chapter 3
authors suggested that plate counting in addition to conductance
measurements (assessment of kinetics in broth used for growth) allowed a
more accurate estimate of number of biofilm cells [188]. However the
conductance measurement may not be possible if other chemicals such as
disinfectant agents are added. It may also be possible for the kinetics to be
disrupted while the cells remain viable but not culturable [161].
Previous authors have suggested that sonication results in the recovery of
more biofilm cells attached to a surface than scraping [195]. With the
exclusion of S. epidermidis on steel, Bjerkan et al. reported that sonication
recovered more S. aureus, Enterococcus faecalis, and Propionibacterium
acnes biofilm cells from steel and titanium implants than scraping methods
[195]. The finding that sonication resulted in recovery of more cells than
scraping or swabbing the surface was also validated through the use of
SEM as discussed in chapter 2. Kobayashi et al. demonstrated that
sonication with vortexing was more effective for recovering S. aureus
biofilm attached to prosthetic device than vortexing alone [196]. Moreover,
through the plate count and molecular biology techniques Kobayasi et al.
reported that the number of biofilm cells recovered from the surface
correlated with an increase in the sonication time allowed, under which
sonication for 30 minutes at 40 kHz resulted in the highest yield of cells
[196].
Monsen evaluated the effect of sonication on viable cells of a number of
gram negative and gram positive organisms [181]. Similar to what was
reported in this thesis, Monsen et al. indicated that for most of the
bacteria sonication for 7 minutes at 20 kHz resulted in no reduction in the
number of viable cells recovered [181]. This suggests that the longer time
periods may have resulted in reducing the number of viable cells possibly
trough the disruptive nature of the sonication process.
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