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Chapter 4
As previously discussed Buckingham-Meyer et al. also used sodium
hypochlorite at multiple concentrations (100mg/L, 500mg/L and 1000mg/L)
to treat Pseudomonas species and Staphylococcal species biofilm on glass
surfaces using four biofilm models, including the CBR [117]. Three of the
methods used had a biofilm development time of 48 hours and two hours
for the dried surface method as described under CEN guidelines EN13697
[117]. The results indicated that exposure to sodium hypochlorite at any of
the concentrations against a 48 hour biofilm developed using the CBR only
resulted in a ~1-2 log 10 reduction. However the use of other methods such
as the dried surface biofilm or the static biofilm method generally resulted
in a much greater log 10 reduction in the number of cells recovered from the
surface (2-4 of reduction) [117, 133]. They also indicated that a two-fold
increase in concentration of sodium hypochlorite had little to no additional
impact [117].
Benzalkonium chloride (molecular formula C 6 H 5 CH 2 N(CH 3 ) 2 RCl) is a
quaternary ammonium compound synthesized from ammonium chloride
(NH 4 Cl) [208]. Previous research has reported multiple species including
Serratia and Pseudomonas species had the ability to proliferate in a low
concentration benzalkonium chloride solution leading to contamination of
the disinfectant product [209-210]. Benzalkonium chloride resistant
bacteria have also been linked to increased resistance to antibiotics [16,
136]. Based on the user concentration recommended by the disinfectant
manufacturer, Vestby et al. used a concentration of 0.02% to investigate if
the ability of Salmonella strains to persist in the environment was
associated with resistance to disinfectants. They reported that a cleaning
product with 0.02% benzalkonium chloride only resulted in marginal
reduction of cells recovered from the surface (0.8-1 log 10 reduction) [113].
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