Research – Staphylococcus and Biofilms – Gram Negative Bacterial Control – Nisin – Ethanol

Nisin and ethanol have been used as antimicrobial agents in food industry. However, nisin alone could not inhibit the growth of gram-negative bacteria, except in combination with a chelating agent, EDTA, or organic acid. This research aimed to study the survival of Escherichia coli O157: H7, Salmonella Typhimurium TISTR 292 and Salmonella Enteritidis DMST 17368 after treatment with nisin at 100, 200, 300, 500, 800, or 1000 IU/mL and ethanol at 70%, 50%, 30%, 20%, or 10% (v/v) alone and in combination. None of all nisin concentrations could reduce the growth of target strains. While 20% ethanol (v/v) having no negative effect on human health, could slightly reduce the growth of target strains. However, the combination of nisin at 500, 800 or 1000 IU/mL and 20% ethanol displayed significant growth reduction at 15 min were below 1 log CFU/mL. Thus, the minimum inhibitory concentration of nisin and ethanol was 500 IU/mL and 20% (v/v), respectively. The release of fatty acid, genetic materials and scanning electron microscope suggested that nisin-ethanol treated cells have altered permeability causing bacterial growth inhibition. Comparison treatment of combined solution and commercial chloride based sanitizer were done for all target strains on stainless steel surface. Survivals of three target strains were below 1 log CFU/mL. The result suggested that combined solution of nisin and ethanol may be a beneficial sanitizer for food industry to inhibit the growth of E. coli O157:H7 and Salmonella sp.

The combination of nisin and ethanol, first report, could inhibit growth of Gram negative bacteria under the mild condition and short time. This combination solution could be used as a sanitizer solution for food industry and reduce the risk of consumer directly contacting on strong chemical agents.

This study investigated the effect of material types (polystyrene, polypropylene, glass, and stainless steel) and glucose addition on Staphylococcus aureus biofilm formation, and the relationship between biofilm formation measured by crystal violet (CV) staining and the number of biofilm cells determined by cell counts was studied. We also evaluated the efficacy of chlorine sanitizer on inhibiting various different types of S. aureus biofilms on the surface of stainless steel. Levels of biofilm formation of S. aureus were higher on hydrophilic surfaces (glass and stainless steel) than on hydrophobic surfaces (polypropylene and polystyrene). With the exception of biofilm formed on glass, the addition of glucose in broth significantly increased the biofilm formation of S. aureus on all surfaces and for all tested strains (P ≤ 0.05). The number of biofilm cells was not correlated with the biomass of the biofilms determined using the CV staining method. The efficacy of chlorine sanitizer against biofilm of S. aureus was not significantly different depending on types of biofilm (P > 0.05). Therefore, further studies are needed in order to determine an accurate method quantifying levels of bacterial biofilm and to evaluate the resistance of bacterial biofilm on the material surface.

Biofilm formation of Staphylococcus aureus on the surface was different depending on the surface characteristics and S. aureus strains. There was low correlation between crystal violet staining method and viable counts technique for measuring levels of biofilm formation of S. aureus on the surfaces. These results could provide helpful information for finding and understanding the quantification method and resistance of bacterial biofilm on the surface.