Which of the following can be diagnosed using dark field microscopy?

 # Which of the following can be diagnosed using dark field microscopy?

A. Spirochaetes

B. Streptococci

C. Corynebacteria

D. Mycobacteria

The correct answer is A. Spirochaetes.

Explanation:

Dark field microscopy is particularly useful for observing organisms that are difficult to stain, such as Spirochaetes (e.g., Treponema pallidum, the causative agent of syphilis). These bacteria are thin and motile, making dark field microscopy ideal for visualizing their morphology and movement.

Streptococci (B), Corynebacteria (C), and Mycobacteria (D) are typically diagnosed using Gram staining, Albert staining, or acid-fast staining, respectively. They do not require dark field microscopy.