Final answer:
The term for the minimum number of microbes required for infection is the infectious dose, with the median infectious dose (ID50) and median lethal dose (LD50) being key indicators of a pathogen's virulence.
Step-by-step explanation:
The term you are looking for that represents the minimum number of microbes required for an infection to proceed is called the infectious dose. This can vary significantly between pathogens. The two primary measures used are the median infectious dose (ID50) which is the amount needed to infect 50% of a test population and the median lethal dose (LD50), the amount needed to kill 50% of a test population.
A lower ID50 generally indicates a higher virulence of a pathogen, meaning it takes fewer microbial cells or particles to cause an infection. Similarly, a lower LD50 indicates a greater potential to cause death in the infected individuals. These values are important in understanding the potential risks associated with various pathogens.