Pathogens include all but which one of the following? disease-causing bacteria, helpful bacteria found in the gut, viruses, microscopic parasites

Helpful bacteria found in the gut are not pathogens.

Explanation:

An organism is said to be pathogenic if it can invade, grow and multiply in an individual host’s body and cause disease in the susceptible host’s body by evading the immune system of the host.

Viruses belong to obligate pathogen because they require the cellular machinery of the host’s body to grow and replicate and thereby will cause disease in the host.  

Disease-causing bacteria are pathogenic like Salmonella, C. difficile, etc.  

Helpful bacteria of the gut also called the human gastroinstestinal or gut microbiota, or the gut flora are those bacteria living in the digestive system of the body and improve the gut health. Gut bacteria like Lactobacillus generally help by:

well, i believe that the answer is 2. : 3