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Chapter 4
found in the food processing environment and may act as a source of
recontamination in food processing plants [203]. Concrete has a high
propensity to support biofilm formation using the CDC biofilm reactor
model as described previously in this thesis. Biofilm formation on concrete
has also been demonstrated elsewhere [71, 141].
4.1.2. The CEN recommendations for reporting disinfectant efficacy
The European Committee for Standardisation (CEN-Comité Européen de
Normalisation) have developed protocols and guidelines for assessing the
efficacy of disinfectant products sold within the European Union [130].
According to the European suspension test (EN1040) a ≥5 log 10 kill
(99.999%) is necessary to prove the efficacy of a disinfectant against P.
aeruginosa or S. aureus in a planktonic broth suspension [131]. It is
recommended that testing is performed at 20°C or room temperature with
a contact time of 5 minutes and incubation at 36-37°C. However as the
standard EN1040 is based on a suspension tests only it does not require
evaluation of the performance of the disinfectant for removal or
destruction when the bacterial cells attached to a surface.
The current standard EN13697:2001 requires a ≥4 log 10 reduction in cells
attached to a surface after contact with an antibacterial agent [133]. The
procedure should be applicable for cultures of P. aeruginosa, S. aureus, E.
coli and Enterococcus hirae. The test should be performed at room
temperature (18-35°C) with a contact time of 5 minutes with optional
additional times of 1, 15, 30 and 60 minutes. A suspension equivalent to a
0.5 McFarland (~1.5-5x10 8 CFU/ml) is made from an overnight culture of
the test bacteria. A small volume (500µl) of the suspension is added to the
face of the surface (stainless steel-grade B finish) within the confines of a
petri dish and allowed to dry at 37°C. After the suspension has dried onto
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