Abstract
BackgroundBacterial biofilms generally contribute to chronic infections and complicate effective treatment outcomes. To date, there have been no reports describing biofilm formation in animal models of septic arthritis caused by Pseudomonas aeruginosa (P. aeruginosa). P. aeruginosa is an opportunistic pathogenic bacterium which can lead to septic arthritis. The purpose of this study was to establish a rabbit model of septic arthritis caused by P. aeruginosa to determine whether it leads to biofilm formation in the knee joint cavity. In addition, we explored the role of cyclic di-GMP (c-di-GMP) concentrations in biofilm formation in rabbit models.MethodsTwenty rabbits were randomly assigned to five groups: PAO1 (n = 4), PAO1ΔwspF (n = 4), PAO1/plac-yhjH (n = 4) infection group, Luria–Bertani (LB) broth (n = 4), and magnesium tetrasilicate (talc) (n = 4) control groups. Inoculation in the rabbit knee of P. aeruginosa or with the same volume of sterile LB or talc in suspension (control group) was used to induce septic arthritis in the animal model. In the infection groups, septic arthritis was caused by PAO1, PAO1ΔwspF, and PAO1/plac-yhjH strains, respectively. Rabbits were euthanized after 7 days, and pathological examination of synovial membrane was performed. The biofilms on the surface of the synovial membrane were observed by scanning electron microscopy, while the biofilms’ fiber deposition was discriminated using peptide nucleic acid-fluorescence in situ hybridization (PNA-FISH).ResultsA rabbit model for knee septic arthritis induced by P. aeruginosa was successfully established. Scanning electron microscopy revealed that PAO1 strains were surrounded in a self-produced extracellular matrix on the surface of synovial membrane and showed biofilm structures. The biofilms in the fibrous deposition were also observed by PNA-FISH. The PNA-FISH assay revealed that the red fluorescence size in the PAO1ΔwspF group was greater than in PAO1 and PAO1/plac-yhjH groups.ConclusionsThis is the first study to provide evidence that P. aeruginosa forms biofilms in a rabbit model for septic knee arthritis. The rabbit model can be used to investigate new approaches to treatment of biofilms in septic arthritis. Furthermore, c-di-GMP is a key signaling molecule which impacts on biofilm formation in rabbit models of knee septic arthritis.
Highlights
Septic arthritis is an invasive disease that can lead to wide articular cartilage and bone defects and irreversible impairment of joint function (Chan et al, 2020; Margaryan et al, 2020)
The specimens were fixed in 10% neutral paraformaldehyde for 24 h and decalcified by 5% dilute hydrochloric acid for 12 h, embedded in wax blocks and cut into 4-mm-thick sections for routine hematoxylin and eosin (H&E) staining; we examined each H&E-stained slide for histopathological changes and measured the thickness of the synovial membrane using an optical microscope, as previously described (Mohammad et al, 2019; Zhang et al, 2020)
To determine whether P. aeruginosa could induce biofilm formation in a rabbit model for septic knee arthritis, rabbits were inoculated with 106 colony-forming units (CFU) of P. aeruginosa (2 ml) in the knee joint through intra-articular injection and were followed for up to 7 days
Summary
Septic arthritis is an invasive disease that can lead to wide articular cartilage and bone defects and irreversible impairment of joint function (Chan et al, 2020; Margaryan et al, 2020). Some studies have reported that most microorganisms are more likely to live in biofilms rather than in planktonic cultures (Costerton et al, 1978; Donlan and Costerton, 2002) These sturdy communities result in a wide variety of adverse effects in many aspects of our daily life, yet it is a significant challenge to eradicate them because biofilms remain incredibly resistant to conventional antimicrobial agents (Blackman et al, 2021; Cendra and Torrents, 2021). The purpose of this study was to establish a rabbit model of septic arthritis caused by P. aeruginosa to determine whether it leads to biofilm formation in the knee joint cavity. We explored the role of cyclic di-GMP (c-di-GMP) concentrations in biofilm formation in rabbit models
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