Characterization and distribution of viridans group streptococci isolated from infectious endophthalmitis and keratitis

ABSTRACT Purpose: The aims of this study were to characterize alpha-hemolytic streptococci among isolates from cases of infectious endophthalmitis and keratitis and to determine their distributions. Methods: The sample included 27 and 35 nonduplicated isolates of alpha-hemolytic streptococci recovered from patients with infectious endophthalmitis (2002-2013) and keratitis (2008-2013), respectively. Isolates were identified by the optochin susceptibility and bile solubility tests, using a biochemical identification system. The minimum inhibitory concentration was determined by the broth microdilution method. Molecular identification was performed by analyses of three constitutive genes and the complementary multilocus sequence. The molecular epidemiology of Streptococcus pneumoniae was investigated using multilocus sequence typing, and the presence of the capsular polysaccharide-encoding gene was assessed using conventional polymerase chain reaction. Outcomes were evaluated using the patients’ medical records. Results: Phenotypic tests differentiated S. pneumoniae from other alpha-hemolytic streptococci, consistent with later molecular identifications. Streptococcus oralis was significantly prevalent among the endophthalmitis isolates, as was S. pneumoniae in the keratitis isolates. High levels of susceptibility to antibiotics were observed, including vancomycin, cephalosporins, and fluoroquinolones. High genetic variability was detected among the 19 S. pneumoniae strains, with 15 predicted to be encapsulated. The medical records of patients with infectious endophthalmitis were reviewed (n=15/27; 56%), and final visual acuity was assessed in 12 cases (44%). Many patients progressed to a final visual acuity state of “no light perception” (6/12; 50%), “light perception” (3/12; 25%), or “hand motion” (1/12; 8%). The medical records of patients with infectious keratitis were also reviewed (n=24/35; 69%), and final visual acuity was assessed in 18 cases (51%). Similarly, most patients progressed to a final visual acuity state of “no light perception” (6/18; 33%), “light perception” (1/18; 6%), or “hand motion” (6/18; 33%). Overall, the majority of patients progressed to a final visual acuity state of “no light perception” (12/30), “light perception” (4/30), or “hand motion” (7/30). Conclusions: The distribution of alpha-hemolytic streptococci in ocular infections suggested the presence of a species-specific tissue tropism. The prognoses of patients with ocular streptococcal infections were highly unfavorable, and antibiotic resistance did not contribute to the unfavorable clinical progressions and poor outcomes.

摘要
目的：本研究旨在对感染性眼内炎（infectious endophthalmitis）与角膜炎（keratitis）病例分离得到的α-溶血性链球菌（alpha-hemolytic streptococci）进行菌种鉴定，并明确其分布特征。
方法：研究样本分别纳入2002-2013年感染性眼内炎患者分离获得的27株非重复α-溶血性链球菌，以及2008-2013年角膜炎患者分离获得的35株非重复α-溶血性链球菌。采用奥普托欣药敏试验（optochin susceptibility test）、胆汁溶菌试验（bile solubility test）结合生化鉴定系统（biochemical identification system）完成分离株的表型鉴定；通过肉汤微量稀释法（broth microdilution method）测定最低抑菌浓度（minimum inhibitory concentration）；针对3种管家基因（constitutive genes）及互补多位点序列进行分析以开展分子鉴定（molecular identification）；采用多位点序列分型（multilocus sequence typing）对肺炎链球菌（Streptococcus pneumoniae）进行分子流行病学调查；通过常规聚合酶链式反应（polymerase chain reaction, PCR）检测荚膜多糖编码基因（capsular polysaccharide-encoding gene）的存在情况；研究结局通过患者病历资料进行评估。
结果：表型试验可将肺炎链球菌与其他α-溶血性链球菌区分开来，该结果与后续分子鉴定结果一致。在感染性眼内炎分离株中，口腔链球菌（Streptococcus oralis）占比显著较高；而在角膜炎分离株中，肺炎链球菌占比更高。分离株对万古霉素（vancomycin）、头孢菌素类（cephalosporins）及氟喹诺酮类（fluoroquinolones）等抗生素均表现出较高的敏感性。在19株肺炎链球菌中检测到较高的遗传多样性，其中15株被预测为有荚膜包裹。对感染性眼内炎患者的病历资料进行回顾分析（共纳入27例中的15例，占比56%），其中12例（44%）评估了最终视力（visual acuity）情况：6例（50%）最终为无光感（no light perception），3例（25%）为光感（light perception），1例（8%）为手动（hand motion）。对感染性角膜炎患者的病历资料同样进行回顾分析（共纳入35例中的24例，占比69%），其中18例（51%）评估了最终视力情况：6例（33%）最终为无光感，1例（6%）为光感，6例（33%）为手动。整体而言，30例完成视力评估的患者中，多数最终视力状态为无光感（12/30）、光感（4/30）或手动（7/30）。
结论：眼部感染中α-溶血性链球菌的分布特征提示其存在物种特异性的组织嗜性。眼部链球菌感染患者的预后极差，且抗生素耐药性并未参与导致不良的临床进程与不佳结局。