The beneficial effect of milk kefir on respiratory heath has been previously demonstrated; however, water kefir and kefiran in the context of respiratory viral infections have not been investigated. Water kefir and kefiran could be alternatives to milk kefir for their application in persons with lactose intolerance or milk allergy and could be incorporated into vegan diets. Using mice models, this work demonstrated that the oral administration of water kefir or kefiran can modulate the respiratory Toll-like receptor (TLR3)-mediated innate antiviral immunity and improve the resistance to respiratory syncytial virus (RSV) infection. The treatment of mice with water kefir or kefiran for 6 days improved the production of interferons (IFN-β and IFN-γ) and antiviral factors (Mx2, OAS1, RNAseL, and IFITM3) in the respiratory tract after the activation of the TLR3 signaling pathway, differentially modulated the balance of pro- and anti-inflammatory cytokines, reduced RSV replication, and diminished lung tissue damage. Maintaining a proper balance between anti-inflammatory and pro-inflammatory mediators is vital for ensuring an effective and safe antiviral immune response, and the results of this work show that water kefir and kefiran would help to maintain that balance promoting a controlled inflammatory response that defends against infection while minimizing tissue damage.

Orally administered Lacticaseibacillus rhamnosus CRL1505 enhances respiratory immunity, providing protection against respiratory viruses and Streptococcus pneumoniae. However, the capacity of the CRL1505 strain to improve respiratory immunity against Gram-negative bacterial infections has not been evaluated before. The aim of this work was to evaluate whether the Lcb. rhamnosus CRL1505 was able to beneficially regulate the respiratory innate immune response and enhance the resistance to hypermucoviscous KPC-2-producing Klebsiella pneumoniae of the sequence type 25 (ST25). BALB/c mice were treated with the CRL1505 strain via the oral route and then nasally challenged with K. pneumoniae ST25 strains LABACER 01 or LABACER 27. Bacterial cell counts, lung injuries and the respiratory and systemic innate immune responses were evaluated after the bacterial infection. The results showed that K. pneumoniae ST25 strains increased the levels of TNF-α, IL-1β, IL-6, IFN-γ, IL-17, KC and MPC-1 in the respiratory tract and blood, as well as the numbers of BAL neutrophils and macrophages. Mice treated with Lcb. rhamnosus CRL1505 had significantly lower K. pneumoniae counts in their lungs, as well as reduced levels of inflammatory cells, cytokines and chemokines in the respiratory tract and blood when compared to infected controls. Furthermore, higher levels of the regulatory cytokines IL-10 and IL-27 were found in the respiratory tract and blood of CRL1505-treated mice than controls. These results suggest that the ability of Lcb. rhamnosus CRL1505 to help with the control of detrimental inflammation in lungs during K. pneumoniae infection would be a key feature to improve the resistance to this pathogen. Although further mechanistic studies are necessary, Lcb. rhamnosus CRL1505 can be proposed as a candidate to improve patients’ protection against hypermucoviscous KPC-2-producing strains belonging to the ST25, which is endemic in the hospitals of our region.

The immunomodulatory properties of exopolysaccharides (EPSs) produced by Streptococcus thermophilus have not been explored in depth. In addition, there are no comparative studies of the functional properties of EPSs produced by streptococci in different food matrices. In this work, EPSs from S. thermophilus SBC8781 were isolated after soy milk (EPS-s) or cow milk (EPS-m) fermentation, identified, and characterized in their abilities to modulate immunity in porcine intestinal epithelial cells. Fresh soy milk and cow milk were inoculated with S. thermophilus SBC8781 (7 log CFU/mL) and incubated at 37 °C for 24 h. The extraction of EPSs was performed by the ethanol precipitation method. Analytical techniques, including NMR, UV-vis spectroscopy, and chromatography, identified and characterized both biopolymer samples as polysaccharides with high purity levels and similar Mw. EPS-s and EPS-m had heteropolysaccharide structures formed by galactose, glucose, rhamnose, ribose, and mannose, although with different monomer proportions. On the other hand, EPS-s had higher quantities of acidic polymer than EPS-m. The biopolymer production of the SBC8781 strain from the vegetable culture broth was 200–240 mg/L, which was higher than that produced in milk, which reached concentrations of 50–70 mg/L. For immunomodulatory assays, intestinal epithelial cells were stimulated with 100 µg/mL of EPS-s or EPS-m for 48 h and then stimulated with the Toll-like receptor 3 agonist poly(I:C). EPS-s significantly reduced the expression of IL-6, IFN-β, IL-8, and MCP-1 and increased the negative regulator A20 in intestinal epithelial cells. Similarly, EPS-m induced a significant reduction of IL-6 and IL-8 expressions, but its effect was less remarkable than that caused by EPS-s. Results indicate that the structure and the immunomodulatory activity of EPSs produced by the SBC8781 strain vary according to the fermentation substrate. Soy milk fermented with S. thermophilus SBC8781 could be a new immunomodulatory functional food, which should be further evaluated in preclinical trials.

Kefir has been associated with beneficial effects on its host’s health. The previous works examining the impact of kefir on the immune system focused on milk kefir or the exopolysaccharides and bacterial strains derived from it, while water kefir has not been evaluated. Furthermore, studies have focused on kefir’s ability to modulate immune system hemostasis and exert anti-inflammatory effects, while its specific action on antiviral immunity has not been investigated. Thus, the aim of this work was to examine the potential immunomodulatory effects of water kefir on the intestinal innate antiviral immunity mediated by Toll-like receptor-3 (TLR3). Adult BALB/c mice fed water kefir ad libitum, diluted 1:5, 1:10, or 1:20 in the drinking water, for 6 consecutive days. On day 7, the treated groups and the untreated control mice received an intraperitoneal injection of the TLR3 agonist poly(I:C). Two days after the TLR3 activation, the intestinal damage and the innate immune response were studied. The intraperitoneal administration of poly(I:C) induced inflammatory-mediated intestinal tissue damage, characterized by the upregulation of interferons (IFNs), pro-inflammatory mediators (TNF-α, IL-15, IL-6), and factors involved in epithelial destruction (RAE-1 and NKG2D). The histological analysis of small intestinal samples showed that mice receiving water kefir 1:5 exhibited reduced edema and a lower inflammatory cell infiltration. Kefir-treated mice had significantly lower levels of serum LDH, AST, and ALT as well as intestinal TNF-α, IL-15, IL-6, RAE-1, and NKG2D. This group also showed higher concentrations of intestinal IFN-β, IFN-γ, and IL-10. The treatment with 1:10 of water kefir reduced intestinal damage and modulated cytokines but its effect was significantly lower than the 1:5 treatment, while the water kefir 1:20 did not modify the parameters evaluated compared to control mice. The results indicate that water kefir exerts its immunomodulatory effects in a dose-dependent manner. The in vivo studies allow us to speculate that water kefir can induce two beneficial effects on the intestinal TLR3-mediated immune response: the enhancement of antiviral defenses and the protection against the inflammatory-mediated tissue damage. These protective effects of water kefir require further exploration to understand how water kefir, or its specific molecules/strains, can influence the immune response and to determine the extent of its protection against a real viral challenge.

Klebsiella pneumoniae is an opportunistic pathogen that can produce moderate and severe infections in immunosuppressed hosts. In recent years, an increase in the isolation of hypermucoviscous carbapenem-resistant K. pneumoniae with sequence type 25 (ST25) in hospitals in Norwest Argentina was observed. This work aimed to study the virulence and inflammatory potential of two K. pneumoniae ST25 strains (LABACER01 and LABACER27) in the intestinal mucosa. The human intestinal Caco-2 cells were infected with the K. pneumoniae ST25 strains, and their adhesion and invasion rates and changes in the expression of tight junction and inflammatory factors genes were evaluated. ST25 strains were able to adhere and invade Caco-2 cells, reducing their viability. Furthermore, both strains reduced the expression of tight junction proteins (occludin, ZO-1, and claudin-5), altered permeability, and increased the expression of TGF-β and TLL1 and the inflammatory factors (COX-2, iNOS, MCP-1, IL-6, IL-8, and TNF-α) in Caco-2 cells. The inflammatory response induced by LABACER01 and LABACER27 was significantly lower than the one produced by LPS or other intestinal pathogens, including K. pneumoniae NTUH-K2044. No differences in virulence and inflammatory potential were found between LABACER01 and LABACER27. In line with these findings, no major differences between the strains were found when the comparative genomic analysis of virulence factors associated with intestinal infection/colonization was performed. This work is the first to demonstrate that hypermucoviscous carbapenem-resistant K. pneumoniae ST25 infects human intestinal epithelial cells and induces moderate inflammation.

Previously, it was shown that intranasally (i.n.) administered Corynebacterium pseudodiphtheriticum 090104 (Cp) or CP-derived bacterium-like particles (BLPs) improve the immunogenicity of the pneumococcal conjugate vaccine (PCV). This work aimed to deepen the characterization of the adjuvant properties of Cp and CP-derived BLPs for their use in the development of pneumococcal vaccines. The ability of Cp and CP-derived BLPs to improve both the humoral and cellular specific immune responses induced by i.n. administered polysaccharide-based commercial pneumococcal vaccine (Pneumovax 23^®) and the chimeric recombinant PSPF (PsaA-Spr1875-PspA-FliC) protein was evaluated, as well as the protection against Streptococcus pneumoniae infection in infant mice. Additionally, whether the immunization protocols, including Cp and CP-derived BLPs, together with the pneumococcal vaccines can enhance the resistance to secondary pneumococcal pneumonia induced after inflammatory lung damage mediated by the activation of Toll-like receptor 3 (TLR3) was assessed. The results showed that both Cp and CP-derived BLPs increased the immunogenicity and protection induced by two pneumococcal vaccines administered through the nasal route. Of note, the nasal priming with the PSPF T-dependent antigen co-administered with Cp or CP-derived BLPs efficiently stimulated humoral and cellular immunity and increased the resistance to primary and secondary pneumococcal infections. The CP-derived BLPs presented a stronger effect than live bacteria. Given safety concerns associated with live bacterium administration, especially in high-risk populations, such as infants, the elderly, and immunocompromised patients, BLPs emerge as an attractive mucosal adjuvant to improve the host response to pneumococcal infections and to enhance the vaccines already in the market or in development.