What type of bacteria are often found in the normal human microbiota and can outcompete pathogens?

Commensal bacteria are an integral part of the normal human microbiota, which is the collection of microorganisms residing in and on our bodies. These bacteria play a crucial role in maintaining health by occupying niches that would otherwise be available to potential pathogens, thereby outcompeting them for resources and space. By doing so, commensal bacteria help to prevent infections and contribute to a balanced immune response.

Additionally, these bacteria produce substances that can inhibit the growth of harmful pathogens, making it difficult for them to establish themselves in the host. They often engage in beneficial interactions with the host's immune system, stimulating it to function properly and respond to infections more effectively.

In contrast, pathogenic bacteria are those that can cause disease, opportunistic bacteria are typically harmless but can become pathogenic under certain conditions, and invasive bacteria are known for penetrating tissues and causing infection. None of these types serve the protective and competitive roles that commensal bacteria do within the human microbiota.