albicans, which is responsible for at least 85% of human candidiasis (Rein, 1997), and A. neuii, which is the second most frequent microorganism isolated in the Ison and Hay grade II and III vaginal microbiota represented by bacterial vaginosis-related organisms (Verhelst et al., 2005) and has been also associated with bacterial vaginosis in women with intrauterine devices (Chatwani & Amin-Hanjani, 1994). Four of the lactobacilli enhanced the adherence of C. albicans and A. neuii to HeLa cells, which contrasts with previous findings, where pathogen adhesion inhibition was reported (Boris et al.,
1998; Osset et al., 2001). This fact suggests that this trait is strain specific. In fact, although the formation of a ternary complex pathogen–Lactobacillus–epithelial cell might enhance the antimicrobial effect of the lactic acid generated Selleck PD-1 inhibitor by this selleck chemicals bacteria (Boris et al., 1997; Coudeyras et al., 2008), these ternary complexes could also enhance the pathogen adhesion as has been observed with Lactobacillus acidophilus and the adhesion of C. albicans to
the contraceptive vaginal ring (Chassot et al., 2010). Adhesion of A. neuii was very responsive to the addition of the extracellular proteins of the lactobacilli in a strain-dependent fashion. Five of them enhanced adsorption of the pathogen, thus reproducing the results obtained when whole bacterial cells were used. It is worth mentioning the extraordinary adhesion increment brought about by L. gasseri Lv19, which could be due to the secretion of an aggregation-promoting factor–like protein. In fact, it has
already been described that these factors act as bridges between pathogen and human cells (Marcotte et al., 2004). This synergistic effect has also been described for some exopolysaccharides produced by several probiotic Resveratrol bacteria, including L. rhamnosus GG (Ruas-Madiedo et al., 2006). Interestingly, the extracellular proteins of L. plantarum Li69 and of L. salivarius Lv72 markedly inhibited the adhesion of A. neuii to HeLa cells. Among the different proteins secreted by these strains, several contained LysM domains, such as two peptidoglycan-binding proteins of Lv72. The LysM domain has been proposed to be the attachment site of the autolysin AcmA of Lactococcus lactis to peptidoglycan (Steen et al., 2003). Recently, an extracellular chitin-binding protein from L. plantarum, containing this domain, has been shown to attach to the cell surface and to selective bind N-acetylglucosamine-containing polymers (Sánchez et al., 2010). Notably, the Lv19 extracellular proteome, which enhanced A. neuii adhesion, did not include any LysM-bearing polypeptides. It is thus conceivable that binding of the LysM-bearing proteins to the A. neuii surface might block the ligands that recognize the surface of the HeLa cells, as already shown for other proteins (Spurbeck & Arvidson, 2010).