Questions: Many diseases that used to be considered noninfectious probably do involve microbial infection. Give an example of this type of disease and what organism is the culprit?

An example of a disease that was once considered noninfectious but is now known to involve microbial infection is peptic ulcers. The organism responsible for this condition is the bacterium _Helicobacter pylori_.

Explanation:

• Peptic Ulcers: For many years, peptic ulcers were thought to be primarily caused by stress, spicy foods, and excess stomach acid. However, research in the late 20th century revealed that the majority of peptic ulcers are actually caused by an infection with _Helicobacter pylori_.

• ***Helicobacter pylori*:** This bacterium colonizes the stomach lining and can lead to inflammation, which damages the protective mucous layer of the stomach or duodenum, resulting in ulcers. The discovery of this link was so significant that it led to a paradigm shift in the treatment of peptic ulcers, focusing on antibiotic therapy to eradicate the infection.

In summary, peptic ulcers are an example of a disease that was reclassified from noninfectious to infectious due to the identification of _Helicobacter pylori_ as the causative agent.