Nishimura Seisuke, Tsurumoto Toshiyuki, Yonekura Akihiko, Adachi Koichi, Shindo Hiroyuki
Department of Orthopaedic Surgery, Nagasaki University School of Medicine, 1-7-1 Sakamoto, Nagasaki, 852-8501, Japan.
J Orthop Sci. 2006 Jan;11(1):46-50. doi: 10.1007/s00776-005-0968-7.
It is difficult to treat implant-related infections because bacteria form biofilms on implants. Biofilms protect the organisms from the host's immune system and prevent penetration of antimicrobial agents. We investigated the susceptibility of six strains isolated from infected total hip arthroplasty (THA) cases to six antimicrobial agents.
Six Staphylococcus aureus and S. epidermidis strains isolated from infected THA cases and S. aureus ACTT 25923, positive strains of biofilms, were used in this study. Biofilms were developed on 96-well titer plates. After 7 days the nutrient solution was aspirated, and wells were rinsed three times with sterile water. A series of doubling dilutions of each antimicrobial agent (16, 32, 64, 128, 256, 512, and 1024 microg/ml) in trypticase soy broth were added to the wells. The plates were incubated at 37 degrees C. After 24 h, the contents were aspirated and wells were rinsed three times with sterile water. The surfaces of wells were vigorously scraped with a sterile swab and applied to sheep blood agar plates at 37 degrees C in an aerobic chamber for 24 h. The minimum bactericidal concentrations (MBCs) were determined as the lowest concentration of antibiotic resulting in 100% reduction of viable cells compared to the antibiotic-free control. Biofilms were produced on stainless steel washers, and the time-course changes were observed by scanning electron microscopy (SEM).
Planktonic bacteria were sensitive to the antimicrobial agents, but biofilm bacteria were markedly resistant. SEM revealed that biofilms grew larger with time.
The MBCs of antimicrobial agents for biofilms bacteria were higher than those of planktonic bacteria. Therefore, it is suggested that implant-related infection is difficult to treat with antimicrobial agents alone.
植入物相关感染难以治疗，因为细菌会在植入物上形成生物膜。生物膜可保护微生物免受宿主免疫系统的攻击，并阻止抗菌剂的渗透。我们研究了从感染的全髋关节置换术（THA）病例中分离出的6株菌株对6种抗菌剂的敏感性。
本研究使用了从感染的THA病例中分离出的6株金黄色葡萄球菌和表皮葡萄球菌菌株，以及生物膜阳性菌株金黄色葡萄球菌ATCC 25923。在96孔滴定板上形成生物膜。7天后吸出营养液，并用无菌水冲洗孔3次。将每种抗菌剂在胰蛋白酶大豆肉汤中的一系列倍比稀释液（16、32、64、128、256、512和1024μg/ml）加入孔中。平板在37℃下孵育。24小时后，吸出内容物，并用无菌水冲洗孔3次。用无菌拭子大力刮擦孔的表面，并将其接种到37℃有氧培养箱中的羊血琼脂平板上培养24小时。最低杀菌浓度（MBC）被确定为与无抗生素对照相比导致活细胞减少100%的抗生素最低浓度。在不锈钢垫圈上形成生物膜，并通过扫描电子显微镜（SEM）观察其随时间的变化。
浮游细菌对抗菌剂敏感，但生物膜细菌具有明显的抗性。SEM显示生物膜随时间增长。
抗菌剂对生物膜细菌的MBC高于对浮游细菌的MBC。因此，提示仅用抗菌剂难以治疗植入物相关感染。
