# Marine microalgae Biomolecules and Their Adhesion Capacity to _Salmonella enterica_ sv. Typhimurium
## 4 Discussion
Alkaline fractions that exhibited the greatest adhesion capacity (LA-s, GA-s) did not have a high carbohydrate content (around 16%) and exhibited heterogeneous monosaccharide composition with absolute content around 5% glucose, 4% galactose, and 2.3% mannose. This observation suggests that adhesins specificity was not entirely a function of the total amount of particular saccharide structures. The _Salmonella_ adhesion is mediated via protein-carbohydrate or a protein-protein interactions [57], thus proteins and glycosides (SQG and DGG) in alkaline fractions could be synergistically cooperating with polysaccharides binding to bacteria through other mechanisms. For _Salmonella_ Typhimurium, the object of this study, protein-protein interactions are mediated by fimbial and non-fimbrial adhesions and involve the extracellular matrix components of the host cell [58; 59; 60; 61; 62; 63]. Several studies reported that milk and colostrum fractions containing proteins (\(\beta\)-lactoglobulin, \(\alpha\)-lactalbumin) and glycoptides (glycomacropeptide) show anti-adherence properties against _Salmonella_ Typhimurium, _Salmonella enteritidis_, enteropathogenic _Escherichia coli_, and entero hemorrhagic _E. coli_, among others [64; 65; 11; 66]. [PERSON] et al. [67] showed that human-milk-derived sulfated glycolipids inhibited the \(S\). Typhimurium pathogenesis in vitro. The high content of proteins observed in the active microalgal extracts and the presence of glycosides suggested that these molecules might also play an important role in the adhesion process. The aqueous fractions, GW-p or LW-p, with an adhesion capacity similar to the positive control, were composed mainly of (1\(\to\)3)-linked \(\beta\)-glucans, and it is possible that the type-1 adhesins--the most important adhesin found in _Salmonella_--recognized and bound to glucose present in these fractions. [PERSON] et al. [68] determined the binding affinities of the purified FimH lectin from _E. coli_ for several hexoses. The lectin binding site is highly specific for mannose; however, their results showed that FimH can bind to other saccharides, such as fructose and glucose, but their affinity is reduced when compared to mannose. Furthermore, according to [PERSON] et al. [69], the binding-receptor domain interacts with almost all mannose OH groups, indicating that a glycosidic linkage at O-3 may not be detrimental for the binding since the unit still contains other OH groups to interact. The fractions mainly composed of highly branched (1\(\rightarrow\)3),(1\(\rightarrow\)6)-linked \(\beta\)-glucan, LW-s and GW-s, did not present any potential to adhere to bacteria. This result suggests that unsubstituted O-6 was somehow important for the interaction with \(S\). Typhimuriumium. [PERSON] et al. [69] reported that the O-6 of mannose directly interacts with the backbone of the Asp47 residue, the side-chain oxygen of Asn46 residue, and the NH\({}_{2}\) terminal group of the FimH receptor-binding domain, thereby the substitution at O-6 of glucans may have been deleterious for the binding affinity. [PERSON] et al. [19] correlated the amount of mannan, glucan, and proteins of yeast cell wall fractions and yeast autolyase products from several strains with their binding capacity to _E. coli_ and \(S\). Typhimuriumium. For _Salmonella_, the binding affinity was highly correlated with the presence of glucans, whereas the mannan content was important for _E. coli_ binding. In accordance with [PERSON] et al. [19], we believe that many factors influence the binding affinity to these pathogens, together with the mannan and/or glucan content. The polymer three-dimensional structure is also a critical factor for the adhesion process, considering that a pure standardized mannan did not bind to _E. coli_[70], and _E. coli_ with mannose-specific adhesins did not colonize all mannose-containing tissues [71]. Furthermore, the adhesion process might involve other non-specific, hydrophobic, or electrostatic interactions [72].