Unknown,Transcriptomics,Genomics,Proteomics

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Pathogenic mechanisms of Pseudomonas aeruginosa wound infection in response to murine fascia

ABSTRACT: Wound infections are traditionally thought to occur when microbial burden exceeds the innate clearance capacity of host immune system. Here we introduce the idea that the wound environment itself plays a significant contributory role to wound infection. We developed a clinically relevant murine model of soft tissue infection to explore the role of activation of microbial virulence in response to tissue factors as a mechanism by which pathogenic bacteria cause wound infections. Mice underwent abdominal skin incision and light muscle injury with a crushing forceps versus skin incision alone followed by topical inoculation of Pseudomonas aeruginosa. Pseudomonas aeruginosa whole genome transcriptional profiling demonstrated that fascia induced the activation of multiple genes responsible for the synthesis of the iron scavenging protein pyochelin. Ex-vivo murine fascia homogenates were prepared and Pseudomonas aeruginosa MPAO1 was incubated with an inoculum of the fascia homogenate solution. Pseudomonas aeruginosa MPAO1 incubated under the same condtions without the homogenate was used as the control group. Three biological replicates in each group was used.

ORGANISM(S): Pseudomonas aeruginosa

SUBMITTER: John Alverdy

PROVIDER: E-GEOD-61925 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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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:Pseudomonas aeruginosa is a gram negative pathogen that infects acute wounds such as third degree skin injury and chronic wounds such as diabetic ulcers. Within infection sites, this pathogen exists in specific structures termed as biofilms. Biofilms contribute to enhanced resistance of microorganisms to the host defense and antibiotic treatments. Flagella, pilli and chaperon usher pathway (cup) fimbriae provide initial attachment to host tissue during biofilm development. pvcA-D operon codes for proteins which synthesize a secondary metabolite called paerucumarin. Paerucumarin is an isonitrile functionalized cumarin which is not extensively analyzed. We recently showed that paerucumarin enhances the expression of cup genes and biofilm development. We hypothesize that besides the cup genes pvcA-D operon regulates other P. aeruginosa genes. To test this hypothesis, we compared the transcriptome of P. aeruginosa strain MPAO1 with its pvcA mutant (MPAO1/pvcA). In comparison with MPAO1, 53 genes were differentially expressed in pvcA which included 19 up-regulated and 34 down-regulated genes. Functional characterization of differentially expressed genes indicated that 20 of these genes have been reported as iron regulated genes. Real time PCR confirmed these results and indicated that the expression of pvcAD operon is iron independent. However traditional chrome azurol S (CAS) iron binding assay showed that paerucumarin binds iron either within supernatants of MPAO1 or in solution. In addition, exogenously added paerucumarin enhances the expression of iron repressed genes pvdS and pvdA. Similarly, the level of pvdS gene expression in MPAO1?pvcA was significantly reduced as compared to MPAO1. Further analysis confirmed that paerucumarin binds iron in MPAO1 but does not deliver it inside the cell. The growth of a PAO1 double mutant strain (?pvdD?pchA), defective in iron scavenging systems, grown in iron deficient medium was restricted. However, the growth was restricted even further upon addition of exogenous paerucumarin to bacterial cultures. These results suggest that paerucumarin chelates iron but does not function as an iron scavenging system.

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Pathogenic mechanisms of Pseudomonas aeruginosa wound infection in response to murine fascia

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