What are round-shaped bacteria that can exist alone or in groups called?

The term for round-shaped bacteria that can exist either as single cells or in groups is "cocci." This classification is significant in microbiology because the shape of bacteria is one of the primary characteristics used to identify and categorize them. Cocci can be found in various arrangements depending on how they divide. Some may arrange themselves in clusters, such as staphylococci (grape-like clusters), while others might form chains known as streptococci. Understanding the structure and formation of these bacteria is crucial in infection control and treatment, as different shapes can be associated with distinct pathogenic behaviors and responses to treatments.

In contrast, rods refer to a different shape of bacteria known as bacilli, which are elongated and cylindrical. Spires do not correspond to a recognized bacterial shape and do not contribute to the classification of bacteria based on morphology. Bacilli also specifically define the rod-shaped category, which does not relate to the round shape described in the question. Thus, "cocci" is the correct term for round-shaped bacteria based on their distinctive morphology and ability to form various groupings.