Extraterristrial life is defined as life which does not originate from Earth. In the case of colonizing planets, if human colonists come in contact with them, they may come into conflict with them because Alien lifeforms may react unfavorably to human interference (see however brain), and even if they are unintelligent, they may still be dangerous, e.g. if they are harmful microbes.
One idea about how to solve the problem with harmful microbes. Take a set of cell cultures that contain all the cell types that exists in the body (either human or intelligent alien), expose the cell cultures to the supposedly dangerous sample, and scan the effects. If any deterioration occurs, scan the cell cultures in which the deterioration happens, and compare them to the cell cultures in which no deterioration happens. That comparative study identifies the pathogen even if it is previously unknown. Expose the pathogens to multiple randomized remedies to see which possible remedies actually work. And finally, use the cell cultures to determine which of the working remedies have the least side effects. This technology must probably await its construction until self-sufficient space colonies exist, because on Earth medical companies would lobby/exploit various laws to stop it. But that is no problem for self-sufficient space colonies.
Another solution comes from the fact that it is possible to change your own biology by not justifying things, see Advice of ways to stop justifying, multiple stages of justification poisoning, brain, inheritance of acquired characteristics and self-organization on http://purescience.wikia.com.