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Pseudomonas aeruginosa is an opportunistic pathogen considered a common cause of nosocomial infection with high morbidity and mortality in burn patients. Immunoprophylaxis techniques may lower the mortality rate of patients with burn wounds infected by P. aeruginosa; consequently, this may be an efficient strategy to manage infections caused by this bacterium. Several pathogenic Gram-negative bacteria like P. aeruginosa release outer membrane vesicles (OMVs), and structurally OMV consists of several antigenic components capable of generating a wide range of immune responses. Here, we evaluated the immunogenicity and efficacy of P. aeruginosa PA-OMVs (PA-OMVs) conjugated with the diphtheria toxoid (DT) formulated with alum adjuvant (PA-OMVs-DT + adj) in a mice model of burn wound infection. ELISA results showed that in the group of mice immunized with PA-OMVs-DT + adj conjugated, there was a significant increase in specific antibodies titer compared to non-conjugated PA-OMVs or control groups. In addition, the vaccination of mice with PA-OMVs-DT + adj conjugated generated greater protective effectiveness, as seen by lower bacterial loads, and eightfold decreased inflammatory cell infiltration with less tissue damage in the mice burn model compared to the control group. The opsonophagocytic killing results confirmed that humoral immune response might be critical for PA-OMVs mediated protection. These findings suggest that PA-OMV-DT conjugated might be used as a new vaccine against P. aeruginosa in burn wound infection.

A better understanding of host-microbe interaction as a cross-talk between the gastrointestinal (GI) tract and the gut microbiota by improving the maintenance of GI homeostasis can help treat and prevent GI disorders. Gut microbiota can affect signaling molecules like serotonin, which regulate endocrine systems through the GI tract. While studying the importance of gut microbiota effects in the small intestine is also pivotal in humans' GI health. Here, we investigated the potential role of Akkermansia muciniphila as a next-generation probiotic and its Extracellular Vesicles (EVs) as a post-biotic in regulating the serotonin-related gene system in the duodenum and ileum of the small intestine of mice. A. muciniphila significantly affected the mRNA expression of genes involved in the serotonin system (Tph1, Slc6a4a, Mao, Htr3B, Htr4, and Htr7) in the duodenum and ileum of mice (P < 0.05). Moreover, A. muciniphila-derived EVs could impact the expression of major genes involved in the serotonin system (Tph1, slc6a4a, Mao, Htr3B, Htr4, and Htr7) in the duodenum and ileum of mice (P < 0.05). This study may pave the way for further investigation of the effects of strain-specific probiotics on the serotonergic system, which is currently in its infancy.

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