Final answer:
The correct answer is option c. Otic samples are examined unstained before drying to check for the presence of mites, as they can often be seen without staining. Other microorganisms, like yeast and bacteria, may require negative or Gram staining techniques to highlight important structures and differentiate between species.
Step-by-step explanation:
Otic samples prepared to check for the presence of mites usually are examined unstained before the slide is allowed to dry. This technique is utilized because mites and other parasites can often be seen without the need for staining, aiding in a rapid diagnosis.
A drop of immersion oil can be added before a coverslip is applied to prevent the slide from drying out, which is critical for maintaining the resolution of the specimen under observation when using the oil immersion objective lens. When observing otic samples, the aim is to detect the presence of ectoparasites, such as mites that can cause conditions like otitis externa.
For other entities like yeast and bacteria, staining techniques such as negative staining can be quite useful. The purpose of negative staining, such as using India Ink, is to create a contrast that allows the visualization of structures like capsules, which do not absorb most basic dyes. This staining method is essential for identifying encapsulated yeast like Cryptococcus neoformans or bacteria, which can have important diagnostic implications due to their virulence factors.
Bacterial samples, however, often require a different approach such as Gram staining which involves heat fixation and stains like crystal violet. This type of staining helps differentiate bacterial species based on their cell wall composition and can be critical for identifying bacterial morphology and arrangement.