Comparison of Antibacterial Effect of Cationic Peptide LL-37 and Cefalexin on Clinical Staphylococcus aureus-induced Infection after Femur Fracture Fixation.

OBJECTIVE: Antimicrobial peptides are widely present in nature, with many of the antimicrobial peptides having antimicrobial activity against Gram-positive and Gram-negative bacteria, fungi, parasites, and even coated viruses. Internal fixation of fractures is a reliable technique. However, the fracture is difficult to heal and internal fixation is not easy to maintain after infection. This study aims to verify the antibacterial effect of cationic peptide LL-37 on Staphylococcus aureus, explore the anti-biofilm effects of LL-37, and compare the effects of the cationic peptide LL-37 and Cefalexin in treatment of postoperative infection of femoral fracture in vivo. METHODS: The Staphylococcus aureus was clinically isolated from one patient with clinical infection after the fracture fixation at Wuxi 9th People's Hospital. The cationic peptide LL-37 was synthesized by Shanghai Apeptide Co. Ltd. To compare the effects of the cationic peptide LL-37 and Cefalexin in the treatment of postoperative infection of femoral fracture in vivo, 63 rabbits with internal fixation of femoral fractures were inoculated intravenously with clinically isolated pathogenic bacteria suspensions. Rabbits in the treatment groups were treated with peptide LL-37 and Cefalexin after surgery. Rabbits in the control groups were treated with physiological saline after surgery. The biofilms on internal fixtures were harvested from euthanized rabbits 1 h, 12 h, 1 day, 2 days, and 7 days after injection of LL-37, Cefalexin, or saline and calculated by colony count. The biofilms from treatment and control groups at 7 days were analyzed by fluorescence microscopy. Blood samples were collected at 1 h, 12 h, 1 day, 2 days, and 7 days following peptide LL-37 and Cefalexin injection. RESULTS: The results were compared statistically using Student's t-test or two-way analysis of variance (ANOVA). Cationic peptide LL-37 showed significant inhibitory effects on clinically isolated Staphylococcus aureus (P < 0.05) compared with Cefalexin and control group at 1 day (P = 0.021), 2 days (P = 0.019), and 7 days (P = 0.025). Fluorescent images of the biofilm reveal that the numbers of cells on biofilms are far less than those in the Cefalexin and control groups at 7 days. The levels of Interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and C-reactive protein (CRP) reached a maximum at 2 days following the operation. After the injection of LL-37, there was an increase in the serum IL-6, TNF-α, and CRP contents in rabbits in both groups, however from 1 day postoperative the level of IL-6 (P = 0.034), TNF-α (P = 0.043), and CRP (P = 0.039) decreased significantly compared to the Cefalexin and control group. At 7 days postoperative, the level of IL-6 (P = 0.029), TNF-α (P = 0.033), and CRP (P = 0.027) had reverted to normal levels in LL-37 groups. CONCLUSIONS: Cationic peptide LL-37 may be a promising agent to control internal femoral fracture fixation infection in vivo.