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The World Health Organization has rated multidrug-resistant (MDR) Gram-negative bacteria including Pseudomonas aeruginosa (Ps alpha e) as serious threat to human health. We here addressed whether chronic murine gut inflammation facilitates intestinal MDR Ps alpha e colonization and whether bacterial infection subsequently worsens colonic immunopathology. Converse to wildtype counterparts, Ps alpha e colonized the intestines of IL-10(-/-) mice with chronic colitis following peroral challenge, but did not lead to changes in intestinal microbiota composition. Ps alpha e infection accelerated both macroscopic (i.e. clinical) and microscopic disease (i.e. colonic epithelial apoptosis), that were accompanied by increased intestinal pro-inflammatory immune responses as indicated by elevated colonic numbers of innate and adaptive immune cell subsets and enhanced secretion of pro-inflammatory cytokines such as TNF and IFN-gamma in mesenteric lymph nodes of Ps alpha e-infected as compared to unchallenged IL-10(-/-) mice. Remarkably, Ps alpha e-induced pro-inflammatory immune responses were not restricted to the gut, but could also be observed systemically as indicated by increased TNF and IFN-gamma concentrations in sera upon Ps alpha e-infection. Furthermore, viable commensals originating from the intestinal microbiota translocated to extra-intestinal compartments such as liver, kidney and spleen of Ps alpha e-infected IL-10(-/-) mice with chronic colitis only. Hence, peroral MDR Ps alpha e-infection results in exacerbated colonic as well as systemic pro-inflammatory immune responses during chronic murine colitis.

The World Health Organization has rated multi-drug resistant (MDR) Pseudomonas aeruginosa as serious threat for human health. It is, however, unclear, whether intestinal MDR P. aeruginosa carriage is associated with inflammatory responses in intestinal or even systemic compartments. In the present study, we generated with respect to their microbiota "humanized" mice by human fecal microbiota transplantation of secondary abiotic mice. Following peroral challenge with a clinical P. aeruginosa isolate on two consecutive days, mice harboring a human or murine microbiota were only partially protected from stable intestinal P. aeruginosa colonization given that up to 78% of mice were P. aeruginosa-positive at day 28 post-infection (p.i.). Irrespective of the host-specificity of the microbiota, P. aeruginosa colonized mice were clinically uncompromised. However, P. aeruginosa colonization resulted in increased intestinal epithelial apoptosis that was accompanied by pronounced proliferative/regenerative cell responses. Furthermore, at day 7 p.i. increased innate immune cell populations such as macrophages and monocytes could be observed in the colon of mice harboring either a human or murine microbiota, whereas this held true at day 28 p.i. for adaptive immune cells such as B lymphocytes in both the small and large intestines of mice with murine microbiota. At day 7 p.i., pro-inflammatory cytokine secretion was enhanced in the colon and mesenteric lymph nodes, whereas the anti-inflammatory cytokine IL-10 was down-regulated in the former at day 28 p.i. Strikingly, cytokine responses upon intestinal P. aeruginosa colonization were not restricted to the intestinal tract, but could also be observed systemically, given that TNF and IFN-γ concentrations were elevated in spleens as early as 7 days p.i., whereas splenic IL-10 levels were dampened at day 28 p.i. of mice with human microbiota. In conclusion, mere intestinal carriage of MDR P. aeruginosa by clinically unaffected mice results in pro-inflammatory sequelae not only in intestinal, but also systemic compartments.

Compelling evidence demonstrates the pivotal role of the commensal intestinal microbiota in host physiology and the detrimental effects of its perturbations following antibiotic treatment. Aim of this study was to investigate the impact of antibiotics induced depletion and subsequent restoration of the intestinal microbiota composition on the murine mucosal and systemic immunity. To address this, conventional C57BL/6j mice were subjected to broad-spectrum antibiotic treatment for 8 weeks. Restoration of the intestinal microbiota by peroral fecal microbiota transplantation (FMT) led to reestablishment of small intestinal CD4+, CD8+, and B220+ as well as of colonic CD4+ cell numbers as early as 7 days post-FMT. However, at d28 following FMT, colonic CD4+ and B220+ cell numbers were comparable to those in secondary abiotic (ABx) mice. Remarkably, CD8+ cell numbers were reduced in the colon upon antibiotic treatment, and FMT was not sufficient to restore this immune cell subset. Furthermore, absence of gut microbial stimuli resulted in decreased percentages of memory/effector T cells, regulatory T cells, and activated dendritic cells in the small intestine, colon, mesenteric lymph nodes (MLN), and spleen. Concurrent antibiotic treatment caused decreased cytokine production (IFN-γ, IL-17, IL-22, and IL-10) of CD4+ cells in respective compartments. These effects were, however, completely restored upon FMT. In summary, broad-spectrum antibiotic treatment resulted in profound local (i.e., small and large intestinal), peripheral (i.e., MLN), and systemic (i.e., splenic) changes in the immune cell repertoire that could, at least in part, be restored upon FMT. Further studies need to unravel the distinct molecular mechanisms underlying microbiota-driven changes in immune homeostasis subsequently providing novel therapeutic or even preventive approaches in human immunopathologies.

Secondary abiotic mice generated by broad-spectrum antibiotic treatment provide a valuable tool for association studies with microbiota derived from different vertebrate hosts. We here generated human microbiota-associated (hma) mice by human fecal microbiota transplantation of secondary abiotic mice and performed a comprehensive survey of the intestinal microbiota dynamics in offspring of hma mice over 18 weeks following weaning as compared to their mothers applying both cultural and molecular methods. Mice were maintained under standard hygienic conditions with open cages, handled under aseptic conditions, and fed autoclaved chow and water. Within 1 week post weaning, fecal loads of commensal enterobacteria and enterococci had decreased, whereas obligate anaerobic bacteria such as Bacteroides/Prevotella species and clostridia were stably colonizing the intestines of hma offspring at high loads. Lactobacilli numbers were successively increasing until 18 weeks post weaning in both hma offspring and mothers, whereas by then, bifidobacteria were virtually undetectable in the former only. Interestingly, fecal lactobacilli and bifidobacteria were higher in mothers as compared to their offspring at 5 and 18 weeks post weaning. We conclude that the intestinal microbiota composition changes in offspring of hma mice, but also their mothers over time particularly affecting aerobic and microaerobic species.

Background The incidence of human Campylobacter jejuni infections is progressively increasing worldwide. Probiotic compounds might open up valuable tools to decrease pathogen burden and subsequent pro-inflammatory immune responses, but in vivo data are scarce. Methods and results Secondary abiotic mice generated by broad-spectrum antibiotic treatment were perorally challenged with the commercial probiotic compound VSL#3 consisting of Streptococcus thermophilus, Bifidobacterium breve, Bifidobacterium longum, Bifidobacterium infantis, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus paracasei, and Lactobacillus delbrueckii ssp. bulgaricus) either 5 days before (i.e. prophylactic regimen) or after (i.e. therapeutic regimen) peroral C. jejuni strain 81–176 infection, and analyzed 3 weeks following the initial bacterial re-association. Upon challenge, mice were colonized with the probiotic bacteria and/or C. jejuni at comparable intestinal loads, but co-colonization did not result in reduction of the pathogen burden. Remarkably, prophylactic as well as therapeutic VSL#3 treatment of C. jejuni infected mice ameliorated intestinal apoptosis and pro-inflammatory immune responses as indicated by lower numbers of innate and adaptive immune cell populations in the murine colon upon probiotic prophylaxis or treatment and reduced colonic concentrations of pro-inflammatory mediators including IL-6 and MCP-1. Importantly, concentrations of anti-inflammatory mediators such as IL-10 were significantly elevated in the colon of probiotics treated mice as compared to untreated controls. Strikingly, prophylactic VSL#3 treatment attenuated C. jejuni induced systemic pro-inflammatory responses as indicated by less TNF and IL-12p70 secretion in the spleen of VSL#3 pre-treated as compared to non-treated mice. Conclusion Administration of probiotic formulations such as VSL#3 might open up valuable strategies for prophylaxis and/or treatment of C. jejuni induced intestinal and systemic sequelae in vivo by the suppression of pro-inflammatory and induction of anti-inflammatory responses.

Campylobacter jejuni infections are progressively increasing worldwide. Probiotic treatment might open novel therapeutic or even prophylactic approaches to combat campylobacteriosis. In the present study secondary abiotic mice were generated by broad-spectrum antibiotic treatment and perorally reassociated with a commensal murine Lactobacillus johnsonii strain either 14 days before (i.e. prophylactic regimen) or 7 days after (i.e. therapeutic regimen) peroral C. jejuni strain 81–176 infection. Following peroral reassociation both C. jejuni and L. johnsonii were able to stably colonize the murine intestinal tract. Neither therapeutic nor prophylactic L. johnsonii application, however, could decrease intestinal C. jejuni burdens. Notably, C. jejuni induced colonic apoptosis could be ameliorated by prophylactic L. johnsonii treatment, whereas co-administration of L. johnsonii impacted adaptive (i.e. T and B lymphocytes, regulatory T cells), but not innate (i.e. macrophages and monocytes) immune cell responses in the intestinal tract. Strikingly, C. jejuni induced intestinal, extra-intestinal and systemic secretion of pro-inflammatory mediators (such as IL-6, MCP-1, TNF and nitric oxide) could be alleviated by peroral L. johnsonii challenge. In conclusion, immunomodulatory probiotic species might offer valuable strategies for prophylaxis and/or treatment of C. jejuni induced intestinal, extra-intestinal as well as systemic pro-inflammatory immune responses in vivo.

Background Within seven days following peroral high dose infection with Toxoplasma gondii susceptible conventionally colonized mice develop acute ileitis due to an underlying T helper cell (Th) -1 type immunopathology. We here addressed whether mice harboring a human intestinal microbiota developed intestinal, extra-intestinal and systemic sequelae upon ileitis induction. Methodology/Principal findings Secondary abiotic mice were generated by broad-spectrum antibiotic treatment and associated with a complex human intestinal microbiota following peroral fecal microbiota transplantation. Within three weeks the human microbiota had stably established in the murine intestinal tract as assessed by quantitative cultural and culture-independent (i.e. molecular 16S rRNA based) methods. At day 7 post infection (p.i.) with 50 cysts of T. gondii strain ME49 by gavage human microbiota associated (hma) mice displayed severe clinical, macroscopic and microscopic sequelae indicating acute ileitis. In diseased hma mice increased numbers of innate and adaptive immune cells within the ileal mucosa and lamina propria and elevated intestinal secretion of pro-inflammatory mediators including IFN-γ, IL-12 and nitric oxide could be observed at day 7 p.i. Ileitis development was accompanied by substantial shifts in intestinal microbiota composition of hma mice characterized by elevated total bacterial loads and increased numbers of intestinal Gram-negative commensals such as enterobacteria and Bacteroides / Prevotella species overgrowing the small and large intestinal lumen. Furthermore, viable bacteria translocated from the inflamed ileum to extra-intestinal including systemic compartments. Notably, pro-inflammatory immune responses were not restricted to the intestinal tract as indicated by increased pro-inflammatory cytokine secretion in extra-intestinal (i.e. liver and kidney) and systemic compartments including spleen and serum. Conclusion/Significance With respect to the intestinal microbiota composition “humanized” mice display acute ileitis following peroral high dose T. gondii infection. Thus, hma mice constitute a suitable model to further dissect the interactions between pathogens, human microbiota and vertebrate host immunity during acute intestinal inflammation.

Background The rising incidence of multidrug resistant (MDR) Gram-negative bacteria including Pseudomonas aeruginosa has become a serious issue in prevention of its spread particularly among hospitalized patients. It is, however, unclear whether distinct conditions such as acute intestinal inflammation facilitate P. aeruginosa infection of vertebrate hosts. Methods and results To address this, we analysed P. aeruginosa infection in human microbiota-associated (hma) mice with acute ileitis induced by peroral Toxoplasma gondii challenge. When perorally infected with P. aeruginosa at day 3 post ileitis induction, hma mice displayed higher intestinal P. aeruginosa loads as compared to hma mice without ileitis. However, the overall intestinal microbiota composition was not disturbed by P. aeruginosa (except for lowered bifidobacterial populations), and the infection did not further enhance ileal immune cell responses. Pro-inflammatory cytokines including IFN-γ and IL-12p70 were similarly increased in ileum and mesenteric lymph nodes of P. aeruginosa infected and uninfected hma mice with ileitis. The anti-inflammatory cytokine IL-10 increased multifold upon ileitis induction, but interestingly more distinctly in P. aeruginosa infected as compared to uninfected controls. Immune responses were not restricted to the intestines as indicated by elevated pro-inflammatory cytokine levels in liver and kidney upon ileitis induction. However, except for hepatic TNF-α levels, P. aeruginosa infection did not result in more distinct pro-inflammatory cytokine secretion in liver and kidney of hma mice with ileitis. Whereas viable intestinal bacteria were more frequently detected in systemic compartments such as spleen and cardiac blood of P. aeruginosa infected than uninfected mice at day 7 following ileitis induction, P. aeruginosa infection did not exacerbate systemic pro-inflammatory sequelae, but resulted in lower IL-10 serum levels. Conclusion Acute intestinal inflammation facilitates infection of the vertebrate host with MDR bacteria including P. aeruginosa and might also pose particularly hospitalized patients at risk for acquisition. Since acute T. gondii induced inflammation might mask immunopathology caused by P. aeruginosa, a subacute or chronic inflammation model might be better suited to investigate the potential role of P. aeruginosa infection in the aggravation of intestinal disease. Electronic supplementary material The online version of this article (doi:10.1186/s13099-017-0154-4) contains supplementary material, which is available to authorized users.