What form of pathogenic bacteria can appear in groups and has a round shape?

The correct answer, which identifies the form of pathogenic bacteria that can appear in groups and has a round shape, is cocci. Cocci are spherical bacteria that can exist as individual cells or can form clusters or chains, depending on how they divide. For instance, when cocci divide in a single plane, they can form chains called streptococci, or when they divide in multiple planes, they can form irregular clusters known as staphylococci. This characteristic of forming groups distinguishes cocci from other bacterial shapes.

In contrast, bacilli refer to rod-shaped bacteria, which do not appear round, while spirilla are spiral-shaped bacteria that also do not have a spherical form. Vibrio are comma-shaped bacteria and similarly do not fit the description of a round shape or grouping characteristic of cocci. Understanding these forms helps in identifying and classifying different bacteria in microbiology, especially in the context of sanitation and disinfection practices.