Question

multiple choice question
although kochs postulates present a logical framework for establishing a particular microbe as the cause of a disease, they cannot always be applied today because ______.

some causative disease agents cannot be grown in pure culture

it is unethical to use animals for medical testing

virtually all pathogens have been identified

molecular methods are much more reliable and rapid

Explanation:

Koch's postulates require isolating and growing the microbe in pure culture. However, many pathogens (like viruses, certain bacteria such as Mycobacterium leprae, and prions) cannot be cultured on artificial media, making the postulates unapplicable for these agents. The other options are incorrect: animal testing is still ethically permitted under regulated conditions, many pathogens remain unidentified, and while molecular methods are useful, they do not negate the core limitation of pure culture requirements for Koch's postulates.

Answer:

A. some causative disease agents cannot be grown in pure culture