Many studies have linked the antimicrobial properties of kefir with the presence of bacteriocins and organic acids. In the present work, results obtained from bacteriostatic and bactericidal studies, and from RP-HPLC, Mass Spectrometry and proton NMR analysis, show that a sample of milk kefir grains is able to produce an antimicrobial fraction, denoted FK-1000, composed of sugars and amino acids, predominantly polymers of alanine, doublets of tyrosine and phenylalanine. Since this fraction is a lyophilized product whose molecular profile is different from bacteriocins and simple carboxylic acids, its antimicrobial effect cannot be attributed to these molecules, or to alcohols or hydrogen peroxide. The fraction is bactericidal against weak-acid-resistant MRSA and weak-acid resistant P. aeruginosa at pH 5, and is bacteriostatic against both pathogens at pH 7. In combination formulation, the FK-1000 fraction is able to increase fivefold the effect of streptomycin against P. aeruginosa and it is not toxic to human epithelial cells at antimicrobial concentrations. 16 S rRNA microbiota analysis of antimicrobial-producing and non-producing kefir grains demonstrated that they are distinct. In summary, the results indicate that milk kefir grains can produce different classes of molecules with potent antibiotic activity against resistant bacteria.
Using clonal phylogenetic methods, it has been demonstrated that O111:H25 atypical enteropathogenic E. coli (aEPEC) strains belong to distinct clones, suggesting the possibility that their ability to interact with different hosts and abiotic surfaces can vary from one clone to another. Accordingly, the ability of O111:H25 aEPEC strains derived from human, cat and dogs to adhere to epithelial cells has been investigated, along with their ability to interact with macrophages and to form biofilms on polystyrene, a polymer used to make biomedical devices. The results demonstrated that all the strains analyzed were able to adhere to, and to form pedestals on, epithelial cells, mechanisms used by E. coli to become strongly attached to the host. The strains also show a Localized-Adherence-Like (LAL) pattern of adhesion on HEp-2 cells, a behavior associated with acute infantile diarrhea. In addition, the O111:H25 aEPEC strains derived either from human or domestic animals were able to form long filaments, a phenomenon used by some bacteria to avoid phagocytosis. O111:H25 aEPEC strains were also encountered inside vacuoles, a characteristic described for several bacterial strains as a way of protecting themselves against the environment. They were also able to induce TNF-α release via two routes, one dependent on TLR-4 and the other dependent on binding of Type I fimbriae. These O111:H25 strains were also able to form biofilms on polystyrene. In summary the results suggest that, regardless of their source (i.e. linked to human origin or otherwise), O111:H25 aEPEC strains carry the potential to cause human disease.
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