Which type of bacteria are primarily known to be harmful?

Pathogenic bacteria are primarily known to be harmful because they possess traits that allow them to invade the body, evade the immune system, and produce toxins that can lead to disease. These bacteria can cause infections, illnesses, and various health complications in humans and other organisms.

In contrast, non-pathogenic bacteria are those that do not cause disease; they may even play beneficial roles in processes like digestion or natural microbial flora maintenance. Beneficial bacteria are known for their positive contributions to health, such as aiding in digestion or providing protection against harmful microbes. Aerobic bacteria are characterized by their need for oxygen to grow, but this classification does not imply whether they are pathogenic or non-pathogenic. Thus, the focus on pathogenic bacteria as harmful stems from their ability to cause various negative health effects.