Slide 1. Candida albicans
This low power (100x) view demonstrates gram-positive rounded structures (yeasts), many with pseudohyphae (branches without septa). Yeasts, such as Candida albicans, are much larger than bacteria.

Slide 2. Candida albicans
This view through an oil-immersion lens (1,000x) shows the large size of Candida albicans. Candida species seldom cause pulmonary infections, even in immunocompromised hosts. Therefore, if yeasts are found in sputum, contamination of the specimen by organisms from the upper respiratory tract should be suspected, especially if the patient has mucosal candidiasis (thrush) or has recently received an antimicrobial agent that allowed overgrowth of yeasts in the oropharynx. In specimens from such patients, squamous epithelial cells are usually abundant. Sometimes, however, Candida is found in good sputum specimens as part of the complex flora in patients who have aspirated large quantities of oropharyngeal flora into the lung (aspiration pneumonia); even then, Candida albicans is rarely pathogenic.

Slide 3. Aspergillus fumigatus
This Gram stain reveals a septate, hyphal organism with a fruiting structure at one end. Several genera of fungi could look similar, but the dichotomous branching at an acute angle suggests Aspergillus species.