Etiology, multidrug resistance, and acute-phase proteins biomarkers as in equine septic arthritis

ABSTRACT: Etiology, multiple antibiotic resistance index, and acute-phase protein profile in the serum and synovial fluid of 44 horses presenting septic arthritis were investigated. Young animals up to 24 months of age not yet submitted to taming were sampled. Synovial samples from the horses were submitted to culture and bacterial isolates subjected to 18 antimicrobials to investigate the in vitro multidrug resistance pattern. Also, hematological aspects, fibrinogen, and serum levels of some acute-phase proteins (total protein, albumin, globulin, amyloid A, and C-reactive protein) were assessed. To statistical analysis, microbiological isolation were divided into four groups: G1 = animals with negative isolation, G2 = isolation of Gram-negative bacteria, G3 = isolation of Gram-positive bacteria), and G4 = isolation of fungi. Microbial isolation was obtained from 77.2% (32/44) of the synovial samples. Escherichia coli (7/44 = 15.9%), Staphylococcus aureus (5/44 = 11.4%), Streptococcus equi subsp. equi (3/44 = 6.8%), Aspergillus niger (3/44 = 6.8%), Pseudomonas aeruginosa (2/44 = 4.5%), Streptococcus equi subsp. zooepidemicus (1/44 = 2.3%), Trueperella pyogenes (1/44 = 2.3%), and Rhodococcus equi (1/44 = 2.3%) were prevalent bacterial agents. Aspergillus niger is reported by the first time as a primary agent of septic arthritis in horses. Gentamicin (84.9%), marbofloxacin (79.3%) and ceftriaxone (72.4%) were the most effective antimicrobials, whereas high resistance of the isolates (>50%) was found to erythromycin (75.9%), clarithromycin (75.9%), penicillin (69%), clindamycin (58.6%), and streptomycin (55.2%). Multiple antibiotic resistance index (≥ 0.3) was identified in 50% (16/32) of the isolates, with highest resistance in Gram-negative bacterial isolates. Serum levels of amyloid A, C-reactive protein, fibrinogen, globulin, and total protein, as well as the number of nucleated cells in the synovial fluid had values above the reference for horses, reinforcing acute-phase proteins as biomarkers in diagnosis of septic arthritis. We highlighted the diversity of microorganisms that may be involved in equine septic arthritis, the high resistance of bacterial isolates to conventional antimicrobials, the high lethality of young horses with septic arthritis, and importance of in vitro antimicrobial susceptibility pattern tests to therapeutic approaches in the disease.摘要：本研究针对44例罹患化脓性关节炎的马匹，对其血清与滑液中的病因学特征、多重抗生素耐药指数以及急性期蛋白谱展开探究。本研究的采样对象为尚未接受驯服的24月龄以内的幼龄马匹。对马匹的滑液样本进行培养，并对分离得到的细菌菌株开展18种抗菌药物的体外药敏试验，以明确其多重耐药模式。同时检测了血液学相关指标、纤维蛋白原以及部分急性期蛋白（acute-phase protein）的血清水平，包括总蛋白、白蛋白、球蛋白、淀粉样蛋白A与C反应蛋白（C-reactive protein）。为开展统计学分析，本研究将微生物分离结果分为四组：G1组为分离结果阴性的马匹，G2组分离到革兰氏阴性菌，G3组分离到革兰氏阳性菌，G4组分离到真菌。77.2%（32/44）的滑液样本可成功分离得到微生物。大肠埃希菌（Escherichia coli，7/44=15.9%）、金黄色葡萄球菌（Staphylococcus aureus，5/44=11.4%）、马链球菌马亚种（Streptococcus equi subsp. equi，3/44=6.8%）、黑曲霉（Aspergillus niger，3/44=6.8%）、铜绿假单胞菌（Pseudomonas aeruginosa，2/44=4.5%）、马链球菌兽疫亚种（Streptococcus equi subsp. zooepidemicus，1/44=2.3%）、化脓隐秘杆菌（Trueperella pyogenes，1/44=2.3%）以及马红球菌（Rhodococcus equi，1/44=2.3%）为主要分离致病菌。本研究首次报道黑曲霉可作为马匹化脓性关节炎的原发性致病菌。庆大霉素（84.9%）、麻保沙星（79.3%）与头孢曲松（72.4%）为抗菌活性最强的药物，而分离菌株对红霉素（75.9%）、克拉霉素（75.9%）、青霉素（69%）、克林霉素（58.6%）以及链霉素（55.2%）呈现高耐药性（耐药率>50%）。50%（16/32）的分离菌株呈现多重抗生素耐药指数≥0.3的特征，其中革兰氏阴性菌分离株的耐药性最高。马匹血清中淀粉样蛋白A、C反应蛋白、纤维蛋白原、球蛋白与总蛋白水平，以及滑液中有核细胞计数均高于参考值范围，进一步证实急性期蛋白可作为化脓性关节炎的诊断生物标志物。本研究强调了参与马匹化脓性关节炎的微生物多样性、细菌分离株对常规抗菌药物的高耐药性、幼龄化脓性关节炎马匹的高致死性，以及体外药敏试验对该病治疗方案制定的重要性。