You are staining bacterial samples for identification and viewing them under a microscope.

This question tests knowledge of bacterial morphology, which is commonly assessed on the NEX Science exam. Bacteria are often classified based on their shape, which helps in identification and diagnosis. The image shows elongated, rod-shaped bacteria. This shape is characteristic ofbacilli. Bacilli are cylindrical or rod-like and are commonly found in many bacterial species, includingEscherichia coliandBacillus anthracis. Cocci are spherical in shape, spirochetes are long and spiral-shaped, and vibrios have a curved, comma-like appearance. None of these shapes match the straight rod-like structures shown in the image. Identifying bacterial shape is an important first step in microbiology before further tests such as Gram staining or biochemical analysis are performed. The NEX exam frequently uses images or descriptions to assess whether students can correctly distinguish between cocci, bacilli, spirilla/spirochetes, and vibrios based on visual characteristics. Recognizing bacilli as rod-shaped bacteria is a key foundational concept.