What are the two primary types of bacteria?

The distinction between pathogenic and non-pathogenic bacteria is fundamental in microbiology. Pathogenic bacteria are those that can cause disease in a host organism, while non-pathogenic bacteria do not cause disease and may even be beneficial to their host. This classification is important for understanding the role of bacteria in health and disease.

Pathogenic bacteria have evolved mechanisms to invade host tissues, evade the immune response, and proliferate, leading to infections and disease symptoms. In contrast, non-pathogenic bacteria often play vital roles in processes such as digestion or protecting against harmful pathogens, highlighting their importance in maintaining a healthy microbiota.

The other choices, while containing terms that are relevant to the study of bacteria, do not provide the foundational categorization typically recognized in microbiology. For instance, symbiotic bacteria involve interactions that are mutually beneficial, but this does not fully capture the core classification of bacteria in terms of their potential to cause disease. Similarly, commensal bacteria live on or in a host without harming it, but they fall under the broader category of non-pathogenic. Therefore, understanding the primary types involves focusing on pathogenic versus non-pathogenic characteristics, which is why this answer is the most accurate.