Treated bacterial endocarditis as a histological mimic of fungal infection

Histological assessment of cardiac valve tissue contributes to the diagnosis of infective endocarditis and is of particular importance in cases in which no organism is cultured. Antibiotic treatment of bacterial endocarditis may lead to abnormal bacterial morphology and staining characteristics. Although in many cases the presence of some residual bacteria of normal appearance makes the diagnosis straightforward, in some only abnormal bacteria may be seen. Unless the appearances of these are interpreted with caution, the presence of larger spherical organisms with the staining properties of a yeast may lead to an erroneous diagnosis of fungal infection.