When you hear "consume" or "metabolize", it doesn't just mean destroying or altering a molecule. The important bit is that energy is removed from the molecule and used by the "organism" in question. Fire definitely does count for that particular one, as the reaction to burn something is almost exactly what we do in our bodies. We burn our food, just much more slowly. A prion though, does not meet that criteria. It does alter a molecule (the non-dangerous form of the prion protein), and energy is removed (the dangerous form of the prion is at a slightly lower energy level, I believe), but the original prion doesn't do anything with that energy. It is unchanged.

Behold, a man!

But yes, examples like fire (nice idea on that one btw) are why "life" is weirdly tricky to define.

Right? The concept of "life" is surprisingly tricky. But I personally would not consider prions to be alive.

I will say though, prions definitely "eat", when they destroy the normal form of the protein. They "grow" by increasing their population, much like bacteria / viruses. Breathing is not a requirement for life.

It really depends who you ask. Some consider viruses to be alive, others do not.

True, a virus can't function unless it's inside a cell with access to those nutrients/cofactors, and existing proteins and other components. But a bacteria also can't function unless it's in an environment with appropriate nutrients/cofactors and existing proteins and other components. The only difference is that those proteins etc already exist when the bacteria is born (divides into daughter cells), while a virus has to go and find them. Does that difference define life?

But then, if you consider a virus to be alive, what about self-replicating plasmids? They're really not much different from a virus. What about transposable elements in a genome? Are they alive too? They're not much different than a virus in latent phase.

The definition of life is something that sounds like it should be easy, and high school textbooks do give a precise definition. But the reality is a lot more complicated and murky than it seems.

We actually can do serotyping by sequence for a bunch of bacterial pathogens. Neisseria meningitidis, for one. Pasteurella multocida for another. Those are two I've done in the past couple months.

Yeah they are. Mostly. Well, it gets weirdly complicated.

Top level. Yes. The isolate has some genotype, which determines its phenotype. The one we're interested in is the antigenic profile, which is to say those "things" that our immune system sees. Some are lipids, some are proteins, some sugars, etc. Our immune system responds in a certain way against a pathogen with one particular antigenic profile, and a somewhat different way against a different isolate of that same species if it has a different antigenic profile. Different isolates are of the same serotype if our immune system responds to them in the same way.

I say mostly, because our human genotype also comes into it. And some species have ways for individuals to hyper-mutate or randomly change parts of their antigenic profile. So serotype doesn't correlate with anything like virulence or antibiotic susceptibility, and is basically meaningless. There are also some species who don't cause an immune response. So they don't really have a serotype. And other species who all cause the same immune reaction, and don't really have serotypes either.

And here's the fun bit. The word "serotype" kind of means different things depending on the species. It's basically defined by the field. Decided at conferences. So there's no actual single true answer to your question. Which is why I say it gets weirdly complicated.