Final answer:
Cocci are round-shaped pathogenic bacteria that can appear singly or in groups, distinguished from rod-shaped bacilli, spiral-shaped spirilla, and curved vibrios.
Step-by-step explanation:
Round-shaped pathogenic bacteria that appear singly or in a group are known as cocci. This bacterial shape is spherical and can be seen in various arrangements after binary fission, such as chains or clusters. Unlike bacilli, which are rod-shaped, or spirilla and vibrios, which are types of curved bacteria, cocci refer strictly to spherical bacteria. An example of cocci bacteria is Staphylococcus, which forms in clusters resembling grapes.