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Food allergies can have significant effects on morbidity and on quality of life. Therefore, the development of efficient approaches to reduce the risk of developing food allergies is of considerable interest. The aim of this study was to identify and select probiotic strains with preventive properties against allergies using a combination of in vitro and in vivo approaches. To that end, 31 strains of bifidobacteria and lactic acid bacteria were screened for their immunomodulatory properties in two cellular models, namely, human peripheral blood mononuclear cells (PBMCs) and T helper 2 (Th2)-skewed murine splenocytes. Six strains inducing a high interleukin-10 (IL-10)/IL-12p70 ratio and a low secretion of IL-4 on the two cellular models were selected, and their protective impact was tested in vivo in a murine model of food allergy to β-lactoglobulin. Three strains showed a protective impact on sensitization, with a decrease in allergen-specific IgE, and on allergy, with a decrease in mast cell degranulation. Analysis of the impact of these three strains on the T helper balance revealed different mechanisms of action. The Lactobacillus salivarius LA307 strain proved to block Th1 and Th2 responses, while the Bifidobacterium longum subsp. infantis LA308 strain induced a pro-Th1 profile and the Lactobacillus rhamnosus LA305 strain induced pro-Th1 and regulatory responses. These results demonstrate that a combination of in vitro and in vivo screening is effective in probiotic strain selection and allowed identification of three novel probiotic strains that are active against sensitization in mice.

The beneficial effects ofBifidobacteriumare partly due to its immunostimulatory properties. These immunostimulatory properties may be linked to the presence of unmethylated CpG motifs specific to bacterial DNA, which may induce a TH1 response by activating Toll-like receptors (TLR). Usingin silicoanalyses, PCR amplification, and dot blotting, we characterized the CpG content of various bifidobacterial strains and evaluated the immunostimulatory properties and genomic heterogeneity of these motifs in the genus. Ourin silicostudy, based on entire genome sequences from five bifidobacterial strains, showed thatBifidobacteriumgenomes contain numerous CpG motifs, including 5′-purine-purine-CG-pyrimidine-pyrimidine-3′ and 5′-purine-TCG-pyrimidine-pyrimidine-3′ motifs, and biologically active sequences previously identified in lactic acid bacteria. We identified four CpG-rich sequences withBifidobacterium longumNCC2705. Two sequences with a percent G+C of about 68% included 14 and 16 CpG motifs. Two sequences with a percent G+C of about 60% included 16 and 6 CpG motifs. These sequences induce the production of monocyte chemoattractant protein 1 (MCP-1) and tumor necrosis factor alpha (TNF-α) through a pattern of TLR9 stimulation on RAW 264.7 macrophages. No link could be established between their immunostimulatory properties, the number of CpG motifs, and percent G+C. We investigated inter- and intraspecies heterogeneity in 71 strains of various origins. These sequences were highly conserved in the genus. No link was found between the presence of the CpG-rich sequence and the origin of the strains (healthy, allergic, or preterm infants). The high frequency of CpG motifs in the DNA ofBifidobacteriummay play an important role in the immunostimulatory properties of commensal or probiotic bifidobacterial strains.

Early-onset group B streptococcal (GBS) infections remain a leading cause of morbidity and mortality in infants. To prevent the vertical transmission of GBS and neonatal GBS infection, guidelines recommend intrapartum penicillin or amoxicillin prophylaxis. This intrapartum antibiotic prophylaxis (IAP) is suspected to favor colonization by antibiotic-resistant bacteria. However, the effects of this prophylaxis on the patterns of acquisition of gastrointestinal bacterial flora in infants have never been studied. We collected stool samples from 3-day-old infants born to mothers who received intrapartum amoxicillin (antibiotic-exposed group; n = 25) and to untreated mothers (non-antibiotic-exposed group; n = 25). The groups were matched for factors known to affect intestinal microbial colonization: gestational age, type of delivery, and type of feeding. Qualitative and quantitative differential analyses of the bacterial flora in stool samples were performed. Similar numbers of infants in the non-antibiotic-exposed and antibiotic-exposed groups were colonized by aerobic bacteria and amoxicillin-resistant enterobacteria (75 and 77%, respectively) ( P = 0.79). In contrast, significantly fewer infants in the antibiotic-exposed group than in the non-antibiotic-exposed group were colonized by anaerobic bacteria, especially Clostridium (12 and 40%, respectively) ( P < 0.05). Regarding intestinal bacterial colonization, the differences between antibiotic-exposed and non-antibiotic-exposed infants were remarkably few. The only statistically significant effect was the reduced initial bacterial colonization by Clostridium in the antibiotic-exposed group. In our study, the use of IAP did not favor colonization by β-lactam-resistant bacteria. However, further evaluations are required to highlight the potential risks of the widespread use of antibiotics to prevent early-onset GBS infection.

Bifidobacterium, which is a dominant genus in infants’ fecal flora and can be used as a probiotic, has shown beneficial effects in various pathologies, including allergic diseases, but its role in immunity has so far been little known. Numerous studies have shown the crucial role of the initial intestinal colonization in the development of the intestinal immune system, and bifidobacteria could play a major role in this process. For a better understanding of the effect ofBifidobacteriumon the immune system, we aimed at determining the impact ofBifidobacteriumon the T-helper 1 (TH1)/TH2 balance by using gnotobiotic mice. Germfree mice were inoculated withBifidobacterium longumNCC2705, whose genome is sequenced, and with nineBifidobacteriumstrains isolated from infants’ fecal flora. Five days after inoculation, mice were killed. Transforming growth factor β1 (TGF-β1), interleukin-4 (IL-4), IL-10, and gamma interferon (IFN-γ) gene expressions in the ileum and IFN-γ, tumor necrosis factor alpha (TNF-α), IL-10, IL-4, and IL-5 secretions by splenocytes cultivated for 48 h with concanavalin A were quantified. TwoBifidobacteriumspecies had no effect (B. adolescentis) or little effect (B. breve) on the immune system.Bifidobacterium bifidum,Bifidobacterium dentium, and oneB. longumstrain induced TH1 and TH2 cytokines at the systemic and intestinal levels. OneB. longumstrain induced a TH2 orientation with high levels of IL-4 and IL-10, both secreted by splenocytes, and of TGF-β gene expression in the ileum. The other two strains induced TH1 orientations with high levels of IFN-γ and TNF-α splenocyte secretions.Bifidobacterium's capacity to stimulate immunity is species specific, but its influence on the orientation of the immune system is strain specific.