Lab 6

Lab 6

Determining causal agents

Multiple Select

Who developed a series of tests to prove a particular microbe causes a particular disease?

• Galileo

• Koch

• Vavilov

• Mendel

Background

• Koch's postulates were developed in the 19th century as general guidelines to identify pathogens that could be isolated with the techniques of the day

• Four rules (postulates) to determining causal agents

Postulate 1

The pathogen must be found associated with the disease in all the diseased plants examined.

Postulate 2

The pathogen must be isolated and grown in pure culture on nutrient media, and its characteristics described (non-obligate parasites), or it must be grown on a susceptible host plant (obligate parasites), and its appearance and effects recorded.

Postulate 3

The pathogen from pure culture must be inoculated on healthy plants of the same species or variety on which the disease appeared, and it must produce the same disease on the inoculated plants.

Postulate 4

The pathogen must be isolated in pure culture again, and its characteristics must be exactly like those observed in step 2

Multiple Choice

Why is step 4 required?

• They had nothing better to do.

• To determine if the plant will survive the disease

• To confirm the causal agent is the same as the original.