Which of the following best describes bacteria that are rod-shaped?

Bacteria that are rod-shaped are best described as bacilli. This term specifically refers to the elongated, cylindrical structure of the bacteria, which can vary in length and width but retains that characteristic rod shape. Bacilli include a wide range of bacteria, some of which can be found in various environments, and can be involved in different processes, such as fermentation or disease.

The other terms refer to different shapes: cocci describe spherical bacteria, spirilla refer to spiral-shaped bacteria, and vibrio are comma-shaped. Each of these morphological classifications helps microbiologists identify and differentiate between the various types of bacteria based on their form, which is essential for understanding their biological functions, potential pathogenicity, and appropriate treatment options.