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Probiotics can release bioactive substances that can inhibit the growth and biofilm formation of pathogenic microorganisms such as Streptococcus mutans. In this context, we evaluated whether the supernatants of Lactobacillus strains isolated from caries-free subjects can inhibit S. mutans, one of the most important bacteria for dental caries. First, the supernatants of 22 Lactobacillus strains were screened for antibacterial activity against S. mutans in planktonic cultures. All 22 Lactobacillus strains studied (100%) showed antibacterial activity. Thereafter, the Lactobacillus strains with the greatest reductions in the planktonic S. mutans cultures were tested on biofilms. The L. fermentum 20.4, L. paracasei 11.6, L. paracasei 20.3 and L. paracasei 25.4 strains could significantly reduce the number of S. mutans cells in biofilms formed in hydroxyapatite (p < 0.05). This reduction was also confirmed by scanning electron microscopy analysis and was not caused by the decreased pH value in the medium (p > 0.05). In addition, the supernatants of these probiotic strains could also reduce the total biomass of S. mutans biofilms (p < 0.05). In conclusion, most of the Lactobacillus strains tested have some antibacterial activity against S. mutans. L. fermentum 20.4, L. paracasei 11.6, L. paracasei 20.3 and L. paracasei 25.4 produce bioactive substances that caused a significant reduction in S. mutans biofilms.

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This study isolated Lactobacillus strains from caries-free subjects and evaluated the inhibitory effects directly on three strains of C. albicans, two clinical strains and one reference strain. Thirty Lactobacillus strains were isolated and evaluated for antimicrobial activity against in vitro C. albicans biofilms. L. paracasei 28.4, L. rhamnosus 5.2 and L. fermentum 20.4 isolates exhibited the most significant inhibitory activity against C. albicans. Co-incubation between these microorganisms resulted in deterrence of biofilm development and retardation of hyphal formation. The hindrance of biofilm development was characterized by the downregulated expression of C. albicans biofilm-specific genes (ALS3, HWP1, EFG1 and CPH1). L. paracasei 28.4, L. rhamnosus 5.2 and L. fermentum 20.4 demonstrated the ability to exert antifungal activity through the inhibition of C. albicans biofilms.

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Probiotics have been described as a potential strategy to control opportunistic infections due to their ability to stimulate the immune system. Using the non-vertebrate model host Galleria mellonella, we evaluated whether clinical isolates of Lactobacillus spp. are able to provide protection against Candida albicans infection. Among different strains of Lactobacillus paracasei, Lactobacillus rhamnosus and Lactobacillus fermentum, we verified that L. paracasei 28.4 strain had the greatest ability to prolong the survival of larvae infected with a lethal dose of C. albicans. We found that the injection of 107 cells/larvae of L. paracasei into G. mellonella larvae infected by C. albicans increased the survival of these insects compared to the control group (P = 0.0001). After that, we investigated the immune mechanisms involved in the protection against C. albicans infection, evaluating the number of hemocytes and the gene expression of antifungal peptides. We found that L. paracasei increased the hemocyte quantity (2.38 x 106 cells/mL) in relation to the control group (1.29 x 106 cells/mL), indicating that this strain is capable of raising the number of circulating hemocytes into the G. mellonella hemolymph. Further, we found that L. paracasei 28.4 upregulated genes that encode the antifungal peptides galiomicin and gallerymicin. In relation to the control group, L. paracasei 28.4 increased gene expression of galiomicin by 6.67-fold and 17.29-fold for gallerymicin. Finally, we verified that the prophylactic provision of probiotic led to a significant reduction of the number of fungal cells in G. mellonella hemolymph. In conclusion, L. paracasei 28.4 can modulate the immune system of G. mellonella and protect against candidiasis.

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Streptococcus mutans and Candida albicans are found together in the oral biofilms on dental surfaces, but little is known about the ecological interactions between these species. Here, we studied the effects of S. mutans UA159 on the growth and pathogencity of C. albicans. Initially, the effects of S. mutans on the biofilm formation and morphogenesis of C. albicans were tested in vitro. Next, we investigate the influence of S. mutans on pathogenicity of C. albicans using in vivo host models, in which the experimental candidiasis was induced in G. mellonella larvae and analyzed by survival curves, C. albicans count in hemolymph, and quantification of hyphae in the host tissues. In all the tests, we evaluated the direct effects of S. mutans cells, as well as the indirect effects of the subproducts secreted by this microorganism using a bacterial culture filtrate. The in vitro analysis showed that S. mutans cells favored biofilm formation by C. albicans. However, a reduction in biofilm viable cells and inhibition of hyphal growth was observed when C. albicans was in contact with the S. mutans culture filtrate. In the in vivo study, injection of S. mutans cells or S. mutans culture filtrate into G. mellonella larvae infected with C. albicans increased the survival of these animals. Furthermore, a reduction in hyphal formation was observed in larval tissues when C. albicans was associated with S. mutans culture filtrate. These findings suggest that S. mutans can secrete subproducts capable to inhibit the biofilm formation, morphogenesis and pathogenicity of C. albicans, attenuating the experimental candidiasis in G. mellonella model.

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Estudos prévios demonstraram que algumas cepas de Lactobacillus podem inibir Streptococcus mutans. Assim, cepas de Lactobacillus pertencentes à microbiota oral residente de indivíduos saudáveis precisam ser investigadas como possíveis estratégias de prevenção para a cárie dentária e outras infecções bucais. O objetivo deste estudo foi avaliar o efeito de cepas do gênero Lactobacillus isoladas de indivíduos livres de cárie sobre S. mutans utilizando modelos de estudo in vitro e in vivo. No estudo in vitro, trinta cepas de Lactobacillus isoladas da cavidade bucal foram avaliadas quanto à atividade antibacteriana contra S. mutans em crescimento planctônico. A seguir, as cinco cepas que apresentaram maior atividade antibacteriana foram selecionadas para o estudo dos efeitos antimicrobianos sobre biofilmes de S. mutans em discos de hidroxiapatita. Para estudo in vivo, foi selecionada a cepa de Lactobacillus com maior efeito inibitório sobre biofilme de S. mutans, procurando-se avaliar seus efeitos no desenvolvimento de cárie experimental em ratos. Os resultados demonstraram que a maioria das cepas de Lactobacillus testadas foi capaz de inibir as células de S. mutans em crescimento planctônico, alcançando percentual de redução de até 99 %. As cepas, com maior percentual de inibição, selecionadas para os testes em biofilme foram uma de L. fermentum e quatro de L. paracasei. Todas as cinco cepas foram capazes de inibir a formação do biofilme de S. mutans, entretanto diferenças estatisticamente significantes só foram observadas para três das cepas testadas. Assim, para os testes de cárie dentária em ratos foi utilizada apenas uma das cepas de L. paracasei. O tratamento com essa cepa levou a uma redução do número de UFC / mL de S. mutans presentes na cavidade bucal dos animais, mas não apresentou efeito sobre o desenvolvimento de cáries dentárias. Em todos os grupos experimentais foram observadas áreas de desmineralização do esmalte, mas lesões cavitárias não foram detectadas. Concluiu-se que as cepas isoladas de L. fermentum e L. paracasei estudadas apresentam potencial probiótico e pode ser consideradas para uso na cavidade bucal, pois possuem atividade inibitória sobre S. mutans e diminuem a formação de biofilme por esse micro-organismo cariogênico (AU)

Previous studies have demonstrated that certain strains of Lactobacillus can inhibit Streptococcus mutans. Thereby, Lactobacillus strains belonging to the oral microbiota resident from healthy subjects need to be investigated as possible strategies to prevent dental caries and other oral infections. The aim of this study was to evaluate the effect of Lactobacillus spp. strains isolated from caries-free subjects on S. mutans using study models in vitro and in vivo. In the in vitro study, thirty Lactobacillus strains recovered from the oral cavity of caries-free subjects were evaluated for antibacterial activity against S. mutans in planktonic culture. Next, the five strains that showed higher antibacterial activity were selected for the study of antimicrobial effects on biofilm of S. mutans formed on hydroxyapatite disks. For in vivo study, we selected the Lactobacillus strain with greater inhibitory effect on S. mutans biofilm, in order to evaluate its effects on the development of experimental caries in rats. The results showed that most of the tested Lactobacillus strains were able to inhibit S. mutans cells in planktonic culture, reaching a percentage reduction up to 99 %. The strains with higher percentage of inhibition selected for biofilm tests were one strain of L. fermentum and four of L. paracasei. All five of these strains were able to inhibit biofilm formation of S. mutans, however statistically significant differences were only observed for three strains. Thus, for the dental caries test in rats was used only one strain of L. paracasei. Treatment with this Lactobacillus strain has led to a reduction in the number of CFU / mL of S. mutans in the oral cavity of the animals but had no effect on the development of dental caries. In all experimental groups enamel demineralization areas were observed, but cavitary lesions were not detected. It was concluded that L. fermentum and L. paracasei strains tested have a potential probiotics and could be used in the oral cavity because they have inhibitory activity against S. mutans and reduce biofilm formation by this cariogenic microorganism(AU)

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