Answer:
Pathogens
Step-by-step explanation:
A pathogen is a foreign organism which enters into our body in order to cause disease or pathological problems. A pathogen can be any kind of organism including bacteria, fungi, virus etc. Different diseases are caused by different kind of organisms. All the problems mentioned in the question like the common cold, the flu, food poisoning, and toothaches are caused by different pathogens. Flu and common cold are caused by viruses while food poisoning and tooth aches are caused by bacteria.