Priming with intranasal lactobacilli prevents Pseudomonas aeruginosa acute pneumonia in mice

Abstract

Background Increasing resistance to antibiotics of Pseudomonas aeruginosa leads to therapeutic deadlock and alternative therapies are needed. We aimed to evaluate the effects of Lactobacillus clinical isolates in vivo, through intranasal administration on a murine model of Pseudomonas aeruginosa pneumonia. Results We screened in vitro 50 pulmonary clinical isolates of Lactobacillus for their ability to decrease the synthesis of two QS dependent-virulence factors (elastase and pyocyanin) produced by Pseudomonas aeruginosa strain PAO1. Two blends of three Lactobacillus isolates were then tested in vivo: one with highly effective anti-PAO1 virulence factors properties (blend named L.rff for L. rhamnosus, two L. fermentum strains), and the second with no properties (blend named L.psb, for L. paracasei, L. salivarius and L. brevis). Each blend was administered intranasally to mice 18 h prior to PAO1 pulmonary infection. Animal survival, bacterial loads, cytological analysis, and cytokines secretion in the lungs were evaluated at 6 or 24 h post infection with PAO1. Intranasal priming with both lactobacilli blends significantly improved 7-day mice survival from 12% for the control PAO1 group to 71 and 100% for the two groups receiving L.rff and L.psb respectively. No mortality was observed for both control groups receiving either L.rff or L.psb. Additionally, the PAO1 lung clearance was significantly enhanced at 24 h. A 2-log and 4-log reduction was observed in the L.rff + PAO1 and L.psb + PAO1 groups respectively, compared to the control PAO1 group. Significant reductions in neutrophil recruitment and proinflammatory cytokine and chemokine secretion were observed after lactobacilli administration compared to saline solution, whereas IL-10 production was increased. Conclusions These results demonstrate that intranasal priming with lactobacilli acts as a prophylaxis, and avoids fatal complications caused by Pseudomonas aeruginosa pneumonia in mice. These results were independent of in vitro anti-Pseudomonas aeruginosa activity on QS-dependent virulence factors. Further experiments are required to identify the immune mechanism before initiating clinical trials.

Lung-Directed Bacteriotherapy in Cystic Fibrosis: Could It Be an Option?

“…The preventive approach may provide a microbiological barrier to hinder lung colonization by pathogenic bacteria through exclusion or competition mechanisms (Figure 1). In line with this view, priming with intranasal administration of lactobacilli has been demonstrated to prevent P. aeruginosa acute pneumonia in mice [65], while preventive treatments with S. salivarius and S. oralis have proved its efficacy in reducing recurrent otitis media in children [67][68][69]. On the other hand, a therapeutic approach carried out during or after antibiotic therapy could take advantage of the antibiotic-mediated reduction in the pathogenic load and consequent increase in the availability of adhesion sites in the lung while contributing to the repopulation of the pulmonary ecosystem with beneficial bacteria.…”

“…The lactobacilli strains also differed for their growth ability and acidification properties in artificial saliva [74]. As reported above, high degree of variability in the antivirulence potential against P. aeruginosa was also reported among Lactobacillus strains isolated from CF respiratory samples [65]. In another study, 57 Lactobacillus strains isolated from milk and yogurt samples were tested for their ability to inhibit the growth and biofilm formation of 80 P. aeruginosa strains [75].…”

“…Additionally, the pulmonary PAO1 burden was significantly reduced at 24 h compared to the control group. Finally, anti-inflammatory activity was observed in mice primed with lactobacilli with a significant reduction in neutrophil recruitment and pro-inflammatory cytokine and chemokine secretion, and an increment in the production of the anti-inflammatory cytokine IL-10 [65].…”

“…Inhaled probiotics could directly compete with pathogens for adhesion to lung mucosa, interfere with pathogen growth and virulence, enhance the integrity of the lung mucosal barrier, and stimulate a local immune response while dampening an excessive inflammatory response (Figure 1). This strategy has demonstrated its efficacy in mice in a number of studies focused on bacterial and viral infections of the respiratory tract [58][59][60][61][62][63][64][65]. Among them, intra-tracheal administration of a mixture of three lactobacilli (L. fermentum K.C6.3.1E, L. paracasei ES.D.88, L. zeae Od.76) was recently demonstrated to protect mice from P. aeruginosa pulmonary infection by reducing the bacterial load in the lung and modulating the cytokine levels [64].…”

“…These observations highlight that this strategy could be efficacious at least against one of the main pulmonary pathogens in CF. In a subsequent study, the same group screened 50 strains of lactobacilli isolated from CF respiratory samples for their ability to inhibit two of the main P. aeruginosa QS-dependent virulence factors (elastase and pyocyanin) [65]. A marked variability in the anti-virulence potential was observed among strains, with 80% of them exhibiting anti-elastolytic activity and 24% anti-pyocyanin activity.…”