Prevention of Initial Bacterial Attachment by Osteopontin and Other Bioactive Milk Proteins

Abstract

A considerable body of work has studied the involvement of osteopontin (OPN) in human physiology and pathology, but comparably little is known about the interaction of OPN with prokaryotic cells. Recently, bovine milk OPN has been proposed as a therapeutic agent to prevent the build-up of dental biofilms, which are responsible for the development of caries lesions. Bioactive milk proteins are among the most exciting resources for caries control, as they hamper bacterial attachment to teeth without affecting microbial homeostasis in the mouth. The present work investigated the ability of OPN to prevent the adhesion of three dental biofilm-forming bacteria to saliva-coated surfaces under shear-controlled flow conditions in comparison with the major milk proteins α-lactalbumin, β-lactoglobulin, αs1-casein, β-casein and κ-casein, as well as crude milk protein. OPN was the most effective single protein to reduce the adhesion of Actinomyces naeslundii, Lactobacillus paracasei subsp. paracasei and Streptococcus mitis. β-casein and crude milk protein also had a pronounced effect on all three species, which suggests binding to different microbial surface structures rather than the blocking of a specific bacterial adhesin. Bioactive milk proteins show potential to delay harmful biofilm formation on teeth and hence the onset of biofilm-related oral disease.

Keywords: actinomyces; bacterial adhesion; biofilms; caseins; dental caries; lactobacillus; microfluidic device; osteopontin; streptococcus.

Figure 1

Effect of osteopontin (OPN), α_s1-casein (A-Cas), β-casein (B-Cas), κ-casein (K-Cas), α-lactalbumin (A-Lac), β-lactoglobulin (B-Lac) and crude skim milk protein (Milk) on the adhesion of Actinomyces naeslundii (a), Lactobacillus paracasei (b) and Streptococcus mitis (c). Summary data from three biological replicates. For each treatment, adhesion was quantified in nine fields of view. Bars normalized to control group. Error bars = SD. * p < 0.05; ** p < 0.01, *** p < 0.001 (One-way ANOVA followed by Dunnett’s post hoc test).

Figure 2

Representative bright field images of adherent bacterial cells. Only osteopontin and crude skim milk protein were able to significantly reduce the attachment of all three bacterial species. PBS = phosphate buffered saline. Bars = 20 µm.