Influenza is one of the important respiratory tract infections that require special attention for maintaining health and hygiene. The removal of influenza virus (IFV) by secretory IgA produced by the respiratory epithelium has been reported to be a critical host defense mechanism. Therefore, we isolated Lactobacillus kunkeei YB38 (YB38), the promoter of the salivary IgA secretion in humans, from honeybee pollen and studied the effect of heat-killed YB38 treatment for preventing IFV infection in a mouse model. Female BALB/c mice received YB38 orally for 21 consecutive days and were then inoculated nasally with IFV. The YB38-treated group with a daily dose of 100 mg/kg showed an increased survival rate after IFV infection relative to the control. IgA secretion in the respiratory epithelium in the YB38-treated group (100 mg/kg) was significantly increased after 6 days of infection, while IL-6 production in the same respiratory site and the number of cells infiltrating into alveoli were significantly decreased. Moreover, lung tissue damage that appeared after IFV infection was reduced. These results suggested that the YB38 dose induced early and local IgA secretion at the infection site, inhibited persistent IFV infection, and prevented the infiltration of inflammatory immune cells or production of excessive IL-6, resulting in less damage to lung tissues.

Patients receiving hemodialysis also manifest gastrointestinal symptoms, such as constipation, caused by restriction of water intake and the loss of body water balance. Because dietary carnitine deficiency is considered to cause smooth muscle dysmotility of the gastrointestinal tract similarly to that in skeletal muscles, carnitine deficiency in hemodialysis patients may be one cause of gastrointestinal discomfort and dysfunctions. We performed a multicenter nonrandomized single-arm prospective clinical trial. Fifteen Japanese patients receiving hemodialysis were administered L-carnitine tablets (900 mg) for 3 months, and clinical and biochemical analyses were performed before and after treatment. The serum total carnitine level was increased significantly by supplementation with L-carnitine for 3 months (from 40.9 ± 2.6 μmol/l to 172.3 ± 19.0 μmol/l, p<0.05). The myasthenia score was decreased significantly by the supplementation (from 1.3 ± 0.3 to 0.8 ± 0.2, p<0.05). The frequency of passing stool tended to increase with the treatment for 3 months (from 4.2 ± 0.5 times/week to 4.8 ± 0.5 times/week). A phyla-level analysis of the microbiota showed that the composition of the individual microbiota was not different between before and after supplementation. A genus-level analysis, however, revealed that the relative abundance of genus Clostridium subcluster 4 was significantly decreased by the supplementation (from 7.7 ± 1.9% to 4.7 ± 1.3%, p<0.05). Oral supplementation of L-carnitine to the patients receiving hemodialysis improved not only their muscle discomfort but also their gastrointestinal disorders and microbiota, although its effect on the prognosis of hemodialysis patients should be further investigated.

Co-culture of lactic acid bacteria (LAB) and yeast induces specific responses that are not observed in pure culture. Gene expression profiles of Lactobacillus paracasei ATCC 334 co-cultured with Saccharomyces cerevisiae IFO 0216 were analyzed by DNA microarray, and the responses induced by direct contact with the yeast cells were investigated. Coating the LAB cells with recombinant DnaK, which acts as an adhesive protein between LAB and yeast cells, enhanced the ratio of adhesion of the LAB cells to the yeast cells. The signals induced by direct contact were clarified by removal of the LAB cells unbound to the yeast cells. The genes induced by direct contact with heat-inactivated yeast cells were very similar to both those induced by the intact yeast cells and those induced by a soluble mannan. The top 20 genes upregulated by direct contact with the heat-inactivated yeast cells mainly encoded proteins related to exopolysaccharide synthesis, modification of surface proteins, and transport systems. In the case of the most upregulated gene, LSEI_0669, encoding a protein that has a region homologous to polyprenyl glycosylphosphotransferase, the expression level was upregulated 7.6-, 11.0-, and 8.8-fold by the heat-inactivated yeast cells, the intact yeast cells, and the soluble mannan, respectively, whereas it was only upregulated 1.8-fold when the non-adherent LAB cells were not removed before RNA extraction. Our results indicated that the LAB responded to direct contact with the yeast cells through recognition of mannan on the surface of the yeast.

Although it is established that the composition of the human intestinal microbiota changes with age, transition of the intestinal microbiota of animals with age has not been well studied. In the present study, we collected fresh fecal samples from dogs of 5 different age groups (pre-weanling, weanling, young, aged, senile) and analyzed the compositions of their intestinal microbiota with a culture-based method. The results suggested that the composition of the canine intestinal microbiota also changes with age. Among intestinal bacteria predominant in dog intestines, lactobacilli appeared to change with age. Both the number and the prevalence of lactobacilli tended to decrease when dogs became older. Bifidobacteria, on the other hand, was not predominant in the intestine of the dogs. We also identified lactobacilli at the species level based on 16S rRNA gene sequences and found that the species composition of Lactobacillus also changed with age. It was further suggested that bacteria species beneficial to host animals may differ depending on the host species.

The influence of soymilk on the fecal microbiota, particularly Bifidobacterium species, and metabolic activities were investigated in eight healthy adult humans. During the soymilk intake period, the number of bifidobacteria in feces was significantly higher (p<0.05) on day 14 of the soymilk intake period than before the intake period, whereas that of Enterobacteriaceae was significantly lower (p<0.05) on days 7 and 14 of the soymilk intake period than before the intake period. In an investigation of Bifidobacterium at the species or group level, the numbers of all species and groups studied slightly increased during the soymilk intake period. These results show that the intake of soymilk may contribute to improving the intestinal environment.

Vaginal lactobacilli (VLB) spread from the mother to the infant during vaginal delivery. However, the effects of VLB on infant intestinal function remain unclear. We investigated the probiotic function and immune effects of VLB on the human embryonic intestinal epithelial cell line INT-407. VLB survived artificial gastric juice and adhered to INT-407 cells. Exposure of INT-407 cells to VLB attenuated both the lipopolysaccharide (LPS)-induced stimulation of interleukin-8 and tumor necrosis factor alpha production and the LPS-stimulated upregulation of TLR4 expression. These results suggest that specific VLB suppresses the inflammation induced by LPS stimulation through downregulation of TLR4 expression in human embryonic intestinal epithelial cells.