Sandbakken Erik Thorvaldsen, Høyer Erling, Witsø Eivind, Søgaard Caroline Krogh, Díez-Sánchez Alberto, Hoang Linh, Wik Tina Strømdal, Bergh Kåre
Department of Orthopedic Surgery, St. Olavs Hospital, Olav Kyrres Gate 13, 7030, Trondheim, Norway.
Department of Neuromedicine and Movement Science, NTNU, Olav Kyrres Gate 13, 7030, Trondheim, Norway.
J Orthop Surg Res. 2024 Dec 4;19(1):820. doi: 10.1186/s13018-024-05309-3.
In diagnosing chronic orthopedic implant infections culture of sonicate represents a supplement to tissue cultures. However, the extent to which biofilm forms on implant surfaces and the degree of dislodgement of bacteria by sonication remains unclear. In this in vivo study using a low bacterial inoculum, we aimed to determine whether a variable effect of sonication could be observed in a standardized in vivo model.
Seven Wistar rats underwent surgery with intramuscular implantation of two bone xenograft implants, each containing two steel plates. The grafts were inoculated with approximately 500 colony forming units (CFU) of Staphylococcus epidermidis ATCC 35984. After 20 days the rats were sacrificed, and the steel plates were removed from the bone grafts. Epifluorescence microscopy and scanning electron microscopy (SEM) were used to visualize biofilm formation and dislodgement on the plate surfaces. In addition to cultures of sonicate, a quantitative S. epidermidis specific PCR was developed for enumeration of bacteria.
A chronic, low-grade implant infection was successfully established, with all animals remaining in good health. All infected bone graft implants yielded abundant growth of S. epidermidis, with a median of 3.25 (1.6-4.6) × 10⁷ CFU per/graft. We were unable to distinguish infected plates from negative controls using epifluorescence microscopy. On infected plates small colonies of staphylococci were identified by SEM. The number of bacteria detected in the sonicate was low with 500 (100-2400) CFU/plate and 475 (140-1821) copies/plate by qPCR. The difference in area covered by fluorescent material before and after sonication was 10.1 (5.7-12.3) %, p = 0.018.
Despite the pronounced infection in the surrounding tissue, only few bacteria were detected on the surface of the steel implants. This is evident from the minimal findings by SEM before sonication, as well as the very low CFU counts and DNA copies in the sonicate. Sonication did not show variable effectiveness, indicating it is a valuable addition to, but not a replacement for biopsy cultures in cases of implant-associated infections with low-virulence microorganisms.
在诊断慢性骨科植入物感染时，超声处理后的培养物是组织培养的一种补充。然而，生物膜在植入物表面形成的程度以及超声处理对细菌的去除程度仍不清楚。在这项使用低细菌接种量的体内研究中，我们旨在确定在标准化的体内模型中是否能观察到超声处理的可变效应。
七只Wistar大鼠接受手术，肌肉内植入两个骨异种移植植入物，每个植入物包含两块钢板。将约500个表皮葡萄球菌ATCC 35984菌落形成单位（CFU）接种到移植物上。20天后处死大鼠，从骨移植物中取出钢板。使用落射荧光显微镜和扫描电子显微镜（SEM）观察钢板表面生物膜的形成和去除情况。除了超声处理后的培养物，还开发了一种定量的表皮葡萄球菌特异性PCR用于细菌计数。
成功建立了慢性、低度植入物感染，所有动物健康状况良好。所有感染的骨移植植入物均有大量表皮葡萄球菌生长，每块移植物的中位数为3.25（1.6 - 4.6）×10⁷CFU。使用落射荧光显微镜，我们无法区分感染的钢板和阴性对照。通过SEM在感染的钢板上鉴定出小的葡萄球菌菌落。超声处理后的培养物中检测到的细菌数量较少，通过qPCR检测为每块钢板500（100 - 2400）CFU和475（140 - 1821）拷贝。超声处理前后荧光物质覆盖面积的差异为10.1（5.7 - 12.3）%，p = 0.018。
尽管周围组织存在明显感染，但在钢植入物表面仅检测到少量细菌。这从超声处理前SEM的微小发现以及超声处理后的培养物中极低的CFU计数和DNA拷贝数可以明显看出。超声处理没有显示出可变的有效性，表明在低毒力微生物引起的植入物相关感染病例中，它是活检培养的有价值补充，但不能替代活检培养。
