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Chapter 4
4. Abstract
In the previous chapter evidence was presented that the density of
Salmonella enterica biofilm can continue to increase over an extended
period of time after it becomes established. There is evidence to suggest
that biofilm formation also enhances bacterial resistance to disinfectant
treatment. The survival of cells may result in bacterial re-growth on
surfaces in the presence of nutrients and favourable conditions resulting in
cross contamination of work-surfaces, equipment or food. This research
evaluated the efficacy of sodium hypochlorite, sodium hydroxide and
benzalkonium chloride against a standard (48 hours) and extended (168
hours) S. enterica biofilm. Sodium hydroxide was effective at eradicating a
standard 48 hour Salmonella biofilm as no viable cells were detected after
a 10 minute contact time. In addition to failure to detect growth by
enumeration of cells following biofilm detachment after sodium hydroxide
exposure, no growth was detected when the entire biofilm attached to a
coupon was placed in broth for 24 hours. However, the same
concentration of sodium hydroxide was not effective at eradicating all
viable cells from an extended biofilm (168 hours). Sodium hypochlorite and
benzalkonium chloride resulted in a reduction of viable cells directly after
exposure however neither of the disinfectants were effective at eliminating
all viable cells from the 48 hour or 168 hour biofilm. Studies on the efficacy
of chemical disinfectants intended for application in the control of biofilm
should include assessment against an established biofilm. In particular
studies should examine a biofilm formed over an extended period of time
as it may be that eradication of established biofilm with standard chemical
disinfectants alone is not possible.
4.1. Introduction
Salmonella readily forms biofilm on food contact surfaces in both industrial
and domestic settings [130]. Salmonella biofilm growth has been examined
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