I couldn't find anything relavant on QuackWatch, but I think I sorta figured this thing out...maybe...

The German study included these comments: "In all of the antimicrobial active grapefruit seed extracts, the preservative benzethonium chloride was detected by thin layer chromatography...Additionally, three extracts contained the preserving substances triclosan and methyl parabene. In only one of the grapefruit seed extracts tested no preservative agent was found."

A Japanese study (link #2) also found the antibacterial additive triclosan, which is used in deodorant soaps and stick deodorants.

One common brand of Grapefruit Seed Extract that's been around for at least several decades uses a manufacturing process that includes this (link #1):

"The main active components in the finished product are a group of quaternary ammonium chlorides, including benzethonium chloride or a compound nearly identical to it, that make up about 8-17% of the product. Benzethonium chloride is a well-known synthetic antiseptic agent; it is not added to the grapefruit extract, but is formed from the original grapefruit flavonoids by the ammoniation process."

So, this all suggests to me that:

1. Naturally processed GFSE probably doesn't have significant antibacterial activity.

2. Benzethonium Chloride, a synthetic antibacterial, has often been found in GFSE over the decades, constituting 8-17% of some products.

3. But the BC isn't "added" to the compound -- it simply materializes as part of the chemical processing of grapefruit seeds when ammonium chloride is added, a by-product of the manufacturing process.

4. Therefore, one person could say "GFSE products don't intrinsically contain antibacterials," and another could say the opposite (since commercial processing is necessary to end up with a cost-effective, concentrated supplement), and both people could be correct in a sense.

5. Separately, the Japanese study in link #2 also detected the addition of triclosan, which the Germans detected in half their samples. This is highly unusual. Or, as the WellVet.com site put it, "Even more curious is the fact that almost all of the grapefruit seed extract products on the market contain preservatives (triclosan and/or methyl parabene) that are intended to prevent the growth of bacteria and fungi! This would make one wonder why, if these extracts were so powerful, the full strength concentrate (which should be far more effective in preventing microbial growth than the label recommended diluted dose) needs any preservative at all?"

http://www.itmonline.org/jintu/grapefruit.htm
http://www.wellvet.com/grapefruitseedextracts.html