Background

Histopathologic differentiation of bacterial endocarditis from yeast-like fungal endocarditis is usually straightforward; however, an underappreciated phenomenon is the effect of antimicrobial therapy on bacterial size, shape and septa (cross-wall) formation resulting in bacterial forms that mimic yeast-like fungi. In this article we illustrate the alterations that occur in antibiotic-treated Staphylococcus aureus endocarditis and compare these changes to histopathologic findings in unaltered S. aureus and Histoplasma endocarditis, respectively.

Methods

Resected valves from three cases of endocarditis were compared based on the type ofinflammatory reaction, organism morphology and culture results. Case 1 was S. aureus endocarditis initially misclassified as Histoplasma due to its atypical morphologic and histopathologic features. The two cases included for comparison were an S. aureus endocarditis with more classic features and an Histoplasma capsulatum endocarditis. Hematoxylin and eosin (H&E), Gram, periodic acid Schiff (PAS), Gomori-Grocott methenamine silver stains (GMS), and culture results were compared in all cases. Molecular and immunohistochemistry tests were used for confirmation of first case. High power oil-immersion was used to visualize organisms’ characteristics in all three cases.

Results

Case 1 and Case 3 (Histoplasma-infected valves) had fibrinous exudates with scattered macrophages. The microorganisms observed in the first case of methicillin-sensitive S. aureus (MSSA) were ∼ 2-3 μm by GMS stain and had prominent septations. Histoplasma yeast were round to oval, ∼ 3-4 μm in size and demonstrated budding. S. aureus without alterations were round, ∼ 1 μm in size, and lacked prominent septations. Necrotizing purulent inflammation was present in the unaltered case of MSSA. The MSSA case with alterations from antibiotic treatment did not stain well with the Gram stain and organisms were best visualized with the PAS and GMS stains.

Conclusions

Antibiotic therapy for bacterial endocarditis can alter the inflammatory reaction to infection, bacterial size, septa formation, and staining characteristics. Knowledge of these therapy-related effects and use of high-power magnification helps to avoid misclassification as yeast-like fungi.

中文翻译：

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模拟真菌生物体的治疗后细菌性心内膜炎：形态学比较和避免这种诊断陷阱的技巧

背景

细菌性心内膜炎与酵母样真菌性心内膜炎的组织病理学区分通常很简单。然而，一个被低估的现象是抗菌疗法对细菌大小、形状和隔（横壁）形成的影响，导致细菌形式模仿酵母样真菌。在本文中，我们说明了抗生素治疗的金黄色葡萄球菌心内膜炎发生的改变，并将这些变化分别与未改变的金黄色葡萄球菌和组织胞浆菌性心内膜炎的组织病理学发现进行了比较。

方法

根据炎症反应的类型、生物体形态和培养结果对3例心内膜炎切除的瓣膜进行比较。病例 1 是金黄色葡萄球菌心内膜炎，由于其非典型的形态学和组织病理学特征，最初被错误分类为组织胞浆菌。包括用于比较的两个病例是具有更典型特征的金黄色葡萄球菌心内膜炎和荚膜组织胞浆菌心内膜炎。比较所有病例的苏木精和伊红 (H&E)、革兰氏菌、高碘酸希夫 (PAS)、Gomori-Grocott 甲胺银染色 (GMS) 和培养结果。分子和免疫组织化学测试用于确认第一例病例。在所有三种情况下，都使用高功率油浸来可视化生物体的特征。

结果

案例 1 和案例 3（组织胞浆菌感染的瓣膜）具有散在巨噬细胞的纤维蛋白渗出物。在第一例甲氧西林敏感的金黄色葡萄球菌(MSSA) 中观察到的微生物通过 GMS 染色约为 2-3 μm，并具有明显的分隔。组织胞浆菌呈圆形至椭圆形，大小约为 3-4 μm，并显示出芽。没有改变的金黄色葡萄球菌是圆形的，大小约为 1 μm，并且没有明显的分隔。在未改变的 MSSA 病例中存在坏死性化脓性炎症。因抗生素治疗而改变的 MSSA 病例不能很好地用革兰氏染色染色，而生物体最好用 PAS 和 GMS 染色进行可视化。

结论

细菌性心内膜炎的抗生素治疗可以改变对感染的炎症反应、细菌大小、隔膜形成和染色特征。了解这些与治疗相关的效果和使用高倍放大镜有助于避免误分类为酵母样真菌。