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Georgieva R., Danguleva A., Stefanova Todorova N., Karapetkov N., Rumyan N., Karaivanova E.
Lactina Ltd., Bulgaria

The rapid growth of probiotic market stimulates more profound examination of already existing probiotic strains or searching of new ones for different applications. Adhesion to host tissues, in particular to epithelial cell line, is a well established probiotic criteria as it provides prolonged persistence in the gut and more efficient host-microbial interaction. Cell-surface hydrophobicity is often considered as the primary factor influencing the strength of bacterial adhesion. In the present study the cell-surface hydrophobicity of 40 lactic acid bacteria and bifidobacteria was measured and the bacteria’ capacity to adhere to human epithelial cells was assessed.

Two groups of Lactobacillus, Bifidobacterium and Streptococcus thermophilus strains from the microbial collection of Lactina Ltd were tested: (i) 22 industrially important strains included in different health formulas and (ii) 18 new potentially probiotic strains interesting for future application. Bacterial cell-surface hydrophobicity was assessed by measuring microbial adhesion to hydrocarbons (MATH) using hexadecane and the percentage of hydrophobicity (H%) was calculated. Human adenocarcinoma cell line HT-29 (ATCC® HTB-38TM) was used for the adhesion assay. The results were expressed as: (i) percentage of adhesion (A%) calculated after determination of cfu/ml of initial and adherent cells on appropriate agar media and (ii) adhesion index- average number of adherent cells in 20 microscopic fields. Bacterial strains were scored as nonadhesive (≤40 bacteria), moderate adhesive (41-100), highly adhesive (101-200) and strongly adhesive (>200 bacteria).

On base of cell surface-hydrophobicity and the adhesion to HT-29 cell line most of the strains were scored as adhesive (77 %), as strains with moderate to high adhesion were the dominant part of the group. Four L. casei/rhamnosus (LLC-J31; LLC-115; LLC-4k; LLRh-V410;), two L. fermentum (LLF-01; LLF-43) strains and 1 Str. thermophilus (LST-Rt4) demonstrated strong adhesion index. Weak adhesion was registered for most L. bulgaricus and L. reuteri strains. All strains (35%) characterized as hydrophobic (H>45%) adhered well to the cell line, but 47 % of the hydrophilic strains (H<17%) including L. helveticus, L. bulgaricus, L. lactis and Str. thermophilus strains were also estimated as good adhesive. Three of the strains into the latter (hydrophilic) group (LLH-108; LLL-14 and LLB-02) showed among the highest percentages of adhesion.

The combined approach for studying the adhesive ability of selected lactic acid bacteria and bifidobacteria gave us good differentiation between nonadhesive and adhesive strains, and also allows discrimination between intermediate (less and more) adhesive strains. Good correlation between adhesion capacity and cell-surface hydrophobicity for hydrophobic strains could be used as precondition for selection of adhesive probiotic cultures in future work. However, the high adhesion capacity of certain hydrophilic strains demonstrates that surface hydrophobicity is not the sole crucial determinant of bacteria-gut epithelium interaction. Therefore, for hydrophilic strains the MATH method should not be used as an estimate for adhesion capability. The obtained valuable information for the possible colonization of human intestine will help for optimization the composition of different probiotic products including strains with more beneficial effects.

Keywords: Probiotic, Adhesion, Hydrophobicity, Lactic acid bacteria, Bifidobacteria

Georgieva R., et al. (2016). Cell-surface hydrophobicity and adhesion ability to human epithelial cell line of industrially important lactic acid bacteria and bifidobacteria. Conference Proceedings of IPC2016. Paper presented at the International Scientific Conference on Probiotics and Prebiotics, Budapest (p. 96.). IPC2016

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