microbiology - How can a pathogenic bacterium be avirulent?
网页2017年5月18日 · 3. Streptococcus pneumoniae is a pathogenic species. Streptococcus pneumoniae R6 is an avirulent strain of this species. Presumably this means that specific virulence genes that are present in virulent strains of Streptococcus pneumoniae are missing or mutated in the R6 strain. In fact the most likely difference would be that virulence …
Why have parasites not evolved to be harmless?
网页Dec 19, 2015 at 3:41. @MarchHo symbiosis actually is much more complicated than parasitism and involves an intricate genetic interaction. Pathogens usually have a reduced genome and to evolve into a harmless species they have to gain a function (which is more difficult than losing one). – WYSIWYG. Dec 19, 2015 at 5:45.
How does HIV mutate into other strains while keeping their …
网页Actually, because of its high mutation rate, HIV produces many failure strains. These strains are even unable to replicate and account for around half of its progenies! So they're certainly avirulent. But these progenies will die out very soon. However, HIV …