Synergistic Effect of Polysaccharide Gums and Antimicrobial Agents on Susceptibility and Protein Expression of Select Pathogenic Microorganisms in Milk

The quest for the use of natural ingredients as preservatives and antimicrobial agents is rising. Polysaccharide gums are usually used as emulsifying agents and as preservatives. The objective of this study was to investigate the combined effect of five different polysaccharide gums and antimicrobial agents on growth, susceptibility and protein expression of select pathogenic microorganisms in milk. Antimicrobial susceptibility and protein concentration were determined by disc diffusion and Pierce BCA assay, respectively. The proteome pattern and the number of protein spots were determined by two-dimensional gel electrophoresis. The results showed that xanthan (6.68±0.02 Log CFU/mL) caused the most growth inhibition of Salmonella enterica, compared to the control. Inclusion of pectin led to a significant (P<0.0001) 2-log reduction of Salmonella enterica during a 2-day refrigerated storage (4 oC). The highest inhibition zones (20.50±0.70) was observed in E. coli O157:H7 exposed to carrageenan-maltodextrin-cefixime. The proteome pattern was impacted by the gums with protein band of size 30kDa being the most prominent band. The highest number of protein spots (35) were obtained in locust bean treated samples. These findings indicated that tested gums affected microbial protein expression and were effective in inhibitory activity against tested pathogens specifically Escherichia coli O157:H7, thus gums hold great promise as some antimicrobial agents. Further characterization of protein targets is warranted.