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Chapter 4
4.3.3. Assessing the efficacy of disinfectants against an established 168
hour biofilm
Table 4.4 summarizes the mean log 10 density of cells recovered from the
concrete test surfaces after the development of a biofilm over an extended
period of time (7 days-168 hours). The mean log 10 density of viable cells
was assessed for four Salmonella strains- S. Typhimurium strains SL1344, S.
Agona SL483, S. Agona outbreak related strain S09-0494 and S. Enteritidis
strain S09-0717. There were limited differences between the 4 strains
when grown for 168 hours on the concrete surfaces.
The mean log 10 density of cells recovered from the S. Typhimurium SL1344
was 9.74 CFU/coupon. After contact with sodium hydroxide for 10 minutes
there was a ~1.5 log 10 reduction in the number of cells recovered
(8.24CFU/coupon). After 90 minutes there was an average of a 2 log 10
reduction in the number of cells recovered from the SL1344 biofilm. This
trend was similar for the two S. Agona strains SL483 and S09-0494.
However, sodium hydroxide was slightly less effective for reducing the
number of cells recovered from the S. Enteritidis biofilm (< 1 log 10
reduction).
Sodium hypochlorite was less effective at reducing the number of cells
than sodium hydroxide. The mean log 10 density of cells recovered from the
S. Typhimurium SL1344 biofilm after 10 minutes exposure was 9.48
CFU/coupon and was only marginally reduced to 9.40 CFU/coupon after 90
minutes exposure which indicates there was ≤0.2 log 10 reduction after
extensive contact with the disinfectant. This suggests that increased time
of exposure appeared to have a limited effect.
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