Efficacy testing of commercial disinfectants against foodborne pathogenic and spoilage microbes in biofilm-constructs

This paper describes the evaluation of poloxamer-hydrogel biofilm-construct s for the routine efficacy testing of disinfectants at normal use strength. Aqueous solutions of poloxamer Pluronic F127 show thermoreversible gelatio n, being liquid at temperatures <15 <degrees>C but firm gels at temperature s >15 degreesC. Chilled poloxamer solutions (30% w/v) were made up in a try ptone soy broth and inoculated with stationary-phase cultures of 14 foodbor ne spoilage microbes, including Pseudomonas, Bacillus, Staphylococcus, Micr ococcus, enterobacteria and a yeast, as well as pathogen test-strains, incl uding Listeria and Salmonella. Drops (either 200 mul or 100 mul) were place d onto pre-warmed, sterile, stainless steel discs held in sealed Petri dish es. The constructs were incubated for 5 h at 30 degreesC and all strains gr ew well in the poloxamer hydrogel. Incubated poloxamer gels and their discs were transferred to solutions of commercial disinfectant formulations cont aining either amphoteric surfactants, hydrogen peroxide with peracetic acid or silver ions, sodium hypochlorite, or alcohols with and without additive s. After 5 min at 25 degreesC the test pieces were removed from the disinfe ctant solution and transferred to a neutraliser at 10-15 degreesC. These te sts were carried out in triplicate. The gets dispersed rapidly, releasing t he cells and enabling a count of the viable cells. All formulations effecte d a >5-log kill of planktonic challenges within 5 min. An effective killing of microbial cells within the biofilm-constructs was shown when the reduct ion was at least 0.3 log units. The results were highly reproducible, with patterns of susceptibility varying as a function of the organism, disinfect ant type, and concentration. The experiments support the view that poloxame r hydrogels can be used for testing the disinfectant efficacy of various fo rmulations against contaminants isolated from food and drink processes.