What is the main effect of pathogenic bacteria on health?

The main effect of pathogenic bacteria on health is to cause disease. Pathogenic bacteria are those specifically capable of causing illness or infections in a host. They can invade the host's body, multiply, and produce toxins that harm tissues, disrupt normal biological functions, and elicit a response from the immune system. Illnesses caused by these bacteria can range from mild to severe, and in some cases, can lead to significant health complications or even death.

In contrast, options such as promoting healing, supporting digestion, and stimulating growth pertain to beneficial bacteria or probiotics. These microorganisms contribute positively to health by aiding in the breakdown of food during digestion, supporting the immune system, and helping to heal through various biological processes. Therefore, the unique characteristic of pathogenic bacteria lies in their potential to harm rather than help, which solidifies their role in the causation of disease.