Which of the following is a characteristic of both cocci and bacilli?

Cocci and bacilli are both types of bacteria distinguished by their shapes—spherical (cocci) and rod-shaped (bacilli). One significant characteristic they share is the potential to cause diseases in humans, animals, or plants. While not all strains of these bacteria are pathogenic, many are known to be responsible for a variety of infections and illnesses.

This characteristic emphasizes the importance of understanding bacterial forms in the study of microbiology and sanitation practices, particularly when it comes to infection control and effective disinfection strategies. The potential for disease highlights the need for proper sanitation and the application of effective disinfection practices in settings where these bacteria may be present.

The other options do not apply: they are single-celled organisms rather than multicellular; they are larger than viruses, which is true in general, but the focus on disease causation is more relevant; and not all cocci or bacilli are harmful, as many play beneficial roles in ecosystems or human health.