Project description:Biofilms have been implicated in delayed wound healing, although the mechanisms by which biofilms impair wound healing are poorly understood. Many species of bacteria produce exotoxins and exoenzymes that may inhibit healing. In addition, oxygen consumption by biofilms, as well as responding leukocytes, may impede wound healing. In this study, we used oxygen microsensors to measure oxygen transects through in vitro-cultured biofilms, biofilms formed in vivo within scabs from a diabetic (db/db) mouse model, and ex vivo human chronic wound specimens. The results show that oxygen levels within mouse scabs had steep gradients that reached minima ranging from 17-72 mmHg on live mice and 6.4-1.1 mmHg on euthanized mice. The oxygen gradients in the mouse scabs were similar to those observed for clinical isolates cultured in vitro and for human ex vivo specimens. No oxygen gradients were observed for heat-killed mouse scabs, suggesting that active metabolism by the viable bacteria and host cells contributed to the reduced oxygen partial pressure of the scabs. To characterize the metabolic activities of the bacteria in the mouse scabs, we performed transcriptomics analyses of Pseudomonas aeruginosa biofilms associated with the db/db mice wounds using Affymetrix microarrays. The results demonstrated that the bacteria expressed genes for metabolic activities associated with cell growth. Interestingly, the transcriptome results indicated that the bacteria within the wounds also experienced oxygen-limitation stress. Among the bacterial genes that were expressed in vivo were genes associated with the Anr-mediated hypoxia-stress response. Other bacterial stress response genes highly expressed in vivo were genes associated with stationary-phase growth, osmotic stress, and RpoH-mediated heat shock stress. Overall, the results support the hypothesis that bacterial biofilms in chronic wounds promote chronicity by contributing to the maintenance of localized low oxygen tensions.

Project description:Biofilms have been implicated in delayed wound healing, although the mechanisms by which biofilms impair wound healing are poorly understood. Many species of bacteria produce exotoxins and exoenzymes that may inhibit healing. In addition, oxygen consumption by biofilms, as well as responding leukocytes, may impede wound healing. In this study, we used oxygen microsensors to measure oxygen transects through in vitro-cultured biofilms, biofilms formed in vivo within scabs from a diabetic (db/db) mouse model, and ex vivo human chronic wound specimens. The results show that oxygen levels within mouse scabs had steep gradients that reached minima ranging from 17-72 mmHg on live mice and 6.4-1.1 mmHg on euthanized mice. The oxygen gradients in the mouse scabs were similar to those observed for clinical isolates cultured in vitro and for human ex vivo specimens. No oxygen gradients were observed for heat-killed mouse scabs, suggesting that active metabolism by the viable bacteria and host cells contributed to the reduced oxygen partial pressure of the scabs. To characterize the metabolic activities of the bacteria in the mouse scabs, we performed transcriptomics analyses of Pseudomonas aeruginosa biofilms associated with the db/db mice wounds using Affymetrix microarrays. The results demonstrated that the bacteria expressed genes for metabolic activities associated with cell growth. Interestingly, the transcriptome results indicated that the bacteria within the wounds also experienced oxygen-limitation stress. Among the bacterial genes that were expressed in vivo were genes associated with the Anr-mediated hypoxia-stress response. Other bacterial stress response genes highly expressed in vivo were genes associated with stationary-phase growth, osmotic stress, and RpoH-mediated heat shock stress. Overall, the results support the hypothesis that bacterial biofilms in chronic wounds promote chronicity by contributing to the maintenance of localized low oxygen tensions. Transcriptional profiling of two independent biological replicates of Pseudomonas aeruginosa biofilms, as grown to 72 hours and used as inocula applied to the murine wounds, was performed. A principle components analysis (PCA) was used to provide an overview of the transcriptome data from the 28-day mouse wound scab, comparing the data to the biofilm inoculum, and to published reports of P. aeruginosa biofilm and planktonic samples. The analysis shows that the transcriptome of the mouse wound scab was distinct from the biofilm inoculum that was applied to the wound, demonstrating a shift in biofilm gene expression following 28 days of infection. We sought to characterize P. aeruginosa activity within biofilms in the mouse wound model by isolating and identifying mRNA from the biofilms used as inocula and from the wound scabs 28 days post infection.

Project description:Bacterial infections of wounds are associated with poor healing and worse scarring. We sought to identify transcriptomic patterns associated with impaired healing of wounds infected with Klebsiella pneumoniae (K.p.) or Pseudomonas aeruginosa (P.a.) using a rabbit ear wound model. Wounds created on post-operative day (POD) 0 were infected on POD3, within the inflammatory phase of healing. On POD4 the infected wounds were harvested for microarray/transcriptome analysis. Other wounds with 24-hour infections were treated with topical antibiotic to promote biofilm formation and harvested on POD6 or POD12. On POD4 before antibiotic treatment, both wounds contained elevated transcripts that enriched predominantly into inflammation/infection-response pathways and functions characteristic of infiltrating leukocytes. But there were 5-fold more elevated transcripts in P.a.- than K.p.-infected wounds. Additionally, unique to P.a.-infected wounds, was a minor network of inflammation/infection-response molecules with predicted upstream regulation predominated by type I interferons. Also on POD4, Dnr-transcripts of both wounds were enriched into stress-response pathways such as EIF2 signaling. But there were 8-fold more Dnr-transcripts in P.a.- than K.p.-infected wounds, and many more of them enriched in the function, cell death, suggesting that resident dermal cells of P.a.-infected wounds failed to survive a more destructive P.a. infection. On POD6, following two days of antibiotic treatment, the biofilm-colonized wounds expressed magnitudes fewer inflammation and stress-response transcripts. However, a single regulatory network of P.a.-infected wounds was found to consist of Upr-transcripts enriching immune/infection-response functions predicted to be regulated by type I interferons, which was similar to the network unique to P.a.-infected wounds on POD4. On POD12, genes expressed by K.p.-infected wounds suggesting healing, while for P.a.-infected wounds they suggested stalled healing. The similarities and differences between the wound responses to these infections further define the molecular foundations of healing impaired by infections. Rabbit ear Wounds created on post-operative day (POD) 0 were infected with Klebsiella pneumoniae (K.p.) or Pseudomonas aeruginosa (P.a.) on POD3 and harvested on POD4 for RNA extraction. Other wounds with 24-hour infections were treated with topical antibiotic to promote biofilm formation and harvested on POD6 or POD12.

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Microsensor and transcriptome signatures of oxygen depletion in biofilms associated with chronic wounds [biofilm inoculum]

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