Final answer:
The evolution of understanding in microbiology was one reason why it was necessary for researchers to update Koch's original postulates.
Step-by-step explanation:
One reason why it was necessary for researchers to update Koch's original postulates is the evolution of understanding in microbiology. As scientists gained more knowledge and insights about microorganisms and diseases, it became evident that all four of Koch's postulates may not apply to every pathogen. For example, the postulates have limited applicability in modern medicine, especially when it comes to certain pathogens like viruses and prions. Therefore, updating Koch's original postulates was important to ensure that they remain relevant and useful in the field of microbiology.