How likely Would Bacteria from the Cambrian Era Be Harmful?

Suppose we uncover a massive deposit of amber, which contains bugs from the cambrian era. Scientists find that the bacteria preserved inside the bodies of the insects are viable. Is it likely that these bacteria could harm modern humans?
If so, what would result? An enormous epidemic?
Or would these ancient bacteria be mostly harmless?

Whatever supplanted the bacteria may be long gone, leaving nothing to stop them from taking over the world.

It pretty much could be the end of the world or it could be a Tuesday like any other, depending on how the Bacteria can find a niche in the modern ecosystem and how well the ecosystem deals with the additional presence.

Since amber is fossilized tree resin, it is impossible to find amber that old.

Don’t quibble. Substitute whatever prehistoric era tree sap might appear in.

Well, it isn’t Cambrian-old, but apparently you can make delicious beer with it:

http://www.fossilfuelsbrewingco.com/

From the front page of that site it looks like exactly your scenario:

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Am I missing something? How did they jump from finding bacterium in a bee to finding the yeast strains?

Journalists are scientifically illiterate. Atoms are molecules, spiders are insects, bacteria are yeast. They’ll use whichever word they think scans better. Happens all the time.

I just had to stop a podcast from How Stuff Works in disgust because the hosts were so scientifically illiterate. According to them, the LHC is guiding beams of light with magnets.

As pan1 implied, there really isn’t enough information to make a determination here. Remember that “bacteria” are an enormously diverse set of organisms, many, if not most of them almost perfectly harmless to humans, and a few that are really really nasty.

Many bacteria have niches where they survive and do no serious harm and actually do some “good”, in the sense of having a symbiotic relationship with other organisms.