Re: Just going to blab about something I'm on to.

If that tooth had a standard root canal, it means its dead - when they seal that dead tooth they cannot properly and fully disinfect all the micro tubules in the tooth, so bacteria is left there. After the tooth is sealed, there is no oxygen available in the tooth (there are no blood vessels transporting oxygen to the site either. So only anerobic bacteria are able to survive in these conditions, and the toxins made by these are very harmful (their environment made of toxic dental materials is partly to blame).

Unless there are anerobic parasites or fungus able to survive in those conditions and reside and proliferate in those narrow tubules its hard to imagine being anything else than bacteria (but I'm open to sugestions).

Unless you dug deep into the roots and remove the posts placed during root canal procedure, it will be hard for you to access the infected area - and if you did go that deep than that is quite a feat.
When I had one of my root canal removed there was a large sack with breeding bacteria attached to one of the roots, while xray showed a "perfectly made root canal", so if you can see the infection its one more reason to consider having the tooth removed.

Good luck
Mike