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Chapter 4
may prevent removal of the bacteria from the surfaces via swabbing,
despite the cells remaining viable [221]. Therefore, it is possible that the
use of disinfectant products with more than one active agent may result in
an under estimation of viable cells remaining [221]. In addition, the high
log 10 reduction of cells may also be a reflection of the biofilm substratum.
As demonstrated in chapter one and two of this thesis, concrete is
associated with a more dense biofilm compared with other surfaces such
as stainless steel. The propensity to support dense biofilm formation may
be due to increased surface roughness which may also increase resistance
to disinfectant agents.
Joseph et al. assessed the log 10 reduction in viable Salmonella cells in
biofilm (48 hour development) after treatment with sodium hypochlorite
(10, 20, 50 and 100 ppm) and iodophor for 5 intervals of 5-35 minutes [71].
The results from the research suggested that inactivation of S.
Weltevreden biofilm with hypochlorite (no cells detected) was faster on
cement and steel than on plastic (15 min vs. 20 minutes). Joseph et al. also
reported that exposure for 20 minutes to 100ppm to hypochlorite
(100mg/L or 0.01% solution) resulted in no viable cells detected [71]. This
does not correlate with the findings reported in this chapter. However, the
use of cotton swabs to remove the biofilm was used in this research
without providing details of confirmation of complete removal via
microscopy or other methods may cast some doubt on the confidence that
can be placed in their conclusions.
4.4.3. The log 10 reduction achieved by benzalkonium chloride
The results presented in this chapter indicated that benzalkonium chloride
was the least effective disinfectant against a 48 hour and 7 day Salmonella
biofilm. The most substantial reduction (1 log 10 reduction) was achieved
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