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

Chapter 4
4.3. Results
4.3.1. Suspension test to establishing Minimum Inhibitory Concentration
(MIC)
Table 4.2 displays the results of the MIC assay which indicates that a
concentration of 0.5M (sodium hydroxide), 250mg/L (sodium hypochlorite)
and 0.01% (benzalkonium chloride) were sufficient to inhibit all bacterial
growth after incubation with the bacterial suspension for 24 hours at 37°C.
The same MIC was reached across all 4 strains used for biofilm research in
this chapter (highlighted in bold). Two of the thirteen strains (S09-0471 and
S09-0004) had a lower MIC.
4.3.2. Assessing the efficacy of three disinfectants against an established
48 hour biofilm
Table 4.3 demonstrates the mean log 10 density of cells recovered from a
biofilm (without contact with any disinfectant agent—control coupons) and
the mean log 10 density of cells recovered from a biofilm after contact with
sodium hydroxide (1M), sodium hypochlorite (500mg/L) and benzalkonium
chloride (0.02%) for 10-, 45- and 90-minutes.
There was very little difference between the mean log 10 density of cells
recovered from the S. Agona SL483 biofilm and the S. Typhimurium SL1344
biofilm not in contact with the disinfectant (control coupons). Treatment
with sodium hydroxide reduced the number of viable cells recovered (for
both S. Agona SL483 and S. Typhimurium SL1344 biofilms). After exposure
for 10-, 45- and 90-minutes with sodium hydroxide no cells were recovered
from the 48 hour biofilm. Therefore the mean log 10 reduction after contact
with sodium hydroxide was 7.63 CFU/coupon (strain SL1344) and 7.66
CFU/coupon (strain SL483). In addition, no cells were recovered when
Page
135