Once attached these organisms are less susceptible to the Nisin is an antibacterial peptide that is proven to be an effective killing effects of sanitizers (1). A novel approach to controlinhibitor of Gram-positive bacteria and can retain much of its ling bacterial biofilms is to inhibit the initial adhesion of original activity when noncovalently immobilized on a surface. bacteria as opposed to removing them once they have ad-The ability of adsorbed nisin to withstand exchange by the milk hered. Nisin (3510 Da), a peptide that when free in solution proteins a-lactalbumin, b-casein, b-lactoglobulin, and bovine seexhibits antimicrobial activity, has been shown to retain rum albumin on surfaces that had been silanized with dichlorodiemuch of its original activity after adsorption to silanized thylsilane to exhibit high and low hydrophobicities was examined silica (2), and treatment of silica surfaces with an adsorbed using in situ ellipsometry and bioassays of nisin activity following layer of nisin has proved effective in inhibiting growth of sequential adsorption with each milk protein. Kinetic behavior was recorded for nisin adsorption for 1 and 8 h, followed in each adhered cells of Listeria monocytogenes (3), a major foodcase by rinsing in protein-free buffer solution and sequential conborne pathogen.
tact with a single milk protein for 4 h. Concerning nisin adsorption
An important problem affecting the long-term stability of to each surface, a higher adsorbed mass was consistently recorded such surface preparations would be elution of adsorbed nisin on the hydrophilic relative to the hydrophobic surface, indepenby other surface-active components dissolved in solution. dent of adsorption time. While desorption was greater from the The purpose of this work was to begin to study some of the hydrophilic surface in the 1-h test, the amount desorbed was quite factors that determine how well immobilized nisin can resist similar on each surface in the 8-h tests. The sequential data were removal by proteins relevant to its area of application. In this interpreted with the assumptions that nisin organization at the work, in situ ellipsometry was used to monitor adsorption of interface involved adsorption in at least two different states, possinisin on silanized silica and its sequential adsorption behavbly existing in more than one layer, and that in the absence of ior with the milk proteins a-lactalbumin (a-lac), b-casein, exchange, upon addition of the second protein, adsorbed mass would increase by an amount equivalent to its experimentally ob-b-lactoglobulin (b-lg), and bovine serum albumin (BSA).
served monolayer coverage. According to this interpretation the mass of nisin exchanged was generally higher on the hydrophobic MATERIALS AND METHODS than on the hydrophilic surface. b-casein was the most effective eluting agent among the proteins studied, while a-lactalbumin was Solution Preparation the least effective. Both bovine serum albumin and b-lactoglobulin were moderately effective in exchanging with adsorbed nisin, with
A pure grade of nisin was obtained from Aplin and Barrett, a greater amount of nisin being removed by bovine serum albumin. Ltd. (Dorset, UK). Activity was indicated as 5 1 10 7 U/g These results were consistent with those of the bioassays, which (Lots NP 26/2 and NP 72). Sodium phosphate buffer solushowed nisin activity was greatest following contact with a-lac tions were prepared using chemicals of analytical grade and and lowest following contact with b-casein.