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Interaction of Staphylococcus aureus cells and silk threads in vitro and in mouse skin
Abstract:
Staphylococcus aureus cell suspension was epicutaneously inoculated on the back skin of cyclophosphamide-treated mice with silk stitches and these sites were occluded. Biopsy specimens were taken from three mice at 1, 3, 6, 12, 24, 48, and 72 h after inoculation and were examined by electron microscopy. Fibril-like structures (glycocalyx) were seen around the S. aureus cells at 1 h. At 3 h, they had extended towards the silk threads. There were microcolonies on the surfaces of the silk threads and at 12 h the S. aureus cells were enclosed in membrane-like structures. The electron density of the membrane-like structures increased over time. After ruthenium red staining, the membrane-like structures and the fibril-like structures were stained positive, suggesting that these structures contain polysaccharide components. With a combination chemotherapy using clarithromycin and ofloxacin, S. aureus cells in the membrane-like structures were degenerated, whereas the use of clarithromycin or ofloxacin alone had little effect. Chlorhexidin gluconate and povidone iodine were effective if they were able to reach the biofilm. The fibril-like structures appeared in vitro only in the presence of silk threads, and were enhanced by the presence of mouse plasma. These structures did not form with formaldehyde-killed S. aureus cells. Thus, S. aureus cells may interact with foreign bodies to form biofilms, thereby evading the effect of antibacterial agents.
Insights
Staphylococcus aureus forms protective biofilms on foreign bodies like silk sutures. This matrix helps bacteria evade antibiotics, necessitating combination therapies for effective treatment.
Area of Science:
- Microbiology
- Biomaterials Science
- Infectious Diseases
Background:
- Staphylococcus aureus is a common pathogen.
- Biofilm formation by S. aureus on medical devices is a significant clinical challenge.
- Understanding biofilm development is crucial for effective treatment strategies.
Purpose of the Study:
- To investigate the in vivo formation of Staphylococcus aureus biofilms on foreign bodies.
- To characterize the structural components of these biofilms.
- To evaluate the efficacy of different antimicrobial agents against S. aureus biofilms.
Main Methods:
- Epicutaneous inoculation of S. aureus on silk sutures in cyclophosphamide-treated mice.
- Electron microscopy examination of biopsy specimens at various time points.
- Ruthenium red staining to identify polysaccharide components.
- In vitro biofilm formation assays.
- Evaluation of antimicrobial agent efficacy (clarithromycin, ofloxacin, chlorhexidine gluconate, povidone iodine).
Main Results:
- Fibril-like structures (glycocalyx) and microcolonies formed around S. aureus within hours.
- S. aureus cells became enclosed in electron-dense, polysaccharide-rich membrane-like structures over time.
- Combination chemotherapy (clarithromycin and ofloxacin) effectively degenerated biofilm-embedded bacteria.
- Single-agent antibiotics and disinfectants were less effective unless they reached the biofilm.
- Biofilm formation in vitro required silk threads and was enhanced by mouse plasma.
Conclusions:
- Staphylococcus aureus interacts with foreign bodies to form biofilms.
- Biofilm matrix components, including polysaccharides, contribute to antibiotic resistance.
- Effective treatment of S. aureus foreign body infections requires strategies that penetrate or disrupt the biofilm.
- Combination chemotherapy shows promise for treating established biofilms.