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Chapter 1
based disinfectant) the strains tested exhibited reduced susceptibility to
antibiotics. This research reported that the adapted S. Typhimurium strains
displayed a fourfold reduction is susceptibility to ciprofloxacin,
chloramphenicol, tetracycline and ampicillin [128].
However other authors have suggested that the use of disinfectants such
as triclosan may actually increase the Salmonella strains susceptibility to
antibiotics such as ciprofloxacin [137]. As a result of contact with triclosan,
Tabak et al. demonstrated that the S. Typhimurium biofilm cells had
increased susceptibility to ciprofloxacin. The treatment involved sequential
treatment of the biofilm (formed on the air-liquid interface) with 500µg ml -
1
of triclosan for 30 minutes followed by 1 hour treatment with
ciprofloxacin solutions (0-500 µg ml -1 ) [137].
1.16.2. Methods for evaluating the efficacy of disinfectants against
Salmonella biofilm
Disinfectant companies often market their products as active against
Salmonella however these claims are often based on suspension test
results on planktonic cells [134]. To investigate the efficacy of disinfectants
in food processing and domestic environments, the methods applied
should be as close to “real life” conditions as possible [130].
Suspension tests are usually performed using a microtitre plate based
system where a panel of disinfectants at fixed concentrations are added to
a known concentration of bacterial culture for a period of time after which
the number of surviving cells is measured either by plate counts, optical
density or staining [132, 138-139]. This method of testing culturable cells
may have some relevance for studying the methods of cell entry and
subsequent killing, however these tests are of limited value in assessing
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