Final answer:
Pathogenic bacteria cause infections, produce toxins, and damage tissues, but they do not break down food in the digestive system; this is the role of non-pathogenic gut microbiota(option b).
Step-by-step explanation:
Pathogenic bacteria are responsible for a range of harmful actions in the human body. However, when considering the options provided, it's clear that pathogenic bacteria are not responsible for breaking down food in the digestive system; rather, this is the role of the normal gut microbiota, which consists of non-pathogenic bacteria that aid in digestion and provide other beneficial functions. Pathogenic bacteria, on the other hand, are known for causing infections, producing toxins, and damaging tissues, which can lead to diseases such as strep throat, tuberculosis, and pneumonia, as well as foodborne illnesses through contamination and intoxication.
Therefore the correct answer is option b) Breaking down food in the digestive system.