Actually, Shigella and E. coli are basically the same bug (not quite, but awfully close) and E. coli that carry Shiga toxin (enterotoxigenic or ETEC) can also cause dysentery. Anything that can kill E. coli will almost certainly kill Shigella as well. V. cholerae is less clear, but likely will also be affected. A possible issue; heavy metal resistance elements (resistance to copper, zinc, cadmium and mercury, at least) are widespread in nature. For more on this, take a look at Simon Silver's (!) work, or some other stuff out there. It seems likely that naturally occuring strains will rapidly develop resistance, since the heavy metal resistance is on transposons. Sorry to be a downer!
That's not a downer - if I say something stupid, I want someone to let me know. I don't have a Ph.D. or anything, just a bunch of microbiology classes. 
I know just enough to be dangerous!
EIEC (enteroinvasive E. coli) that I mentioned are actually the group of E. coli that carry the endothelial-damaging Shiga toxin - ETEC have a toxin that is similar to the cholera toxin, which activates adenylate cyclase and causes hypersecretion. So you get profuse diarrhea (which already doesn't fit the "dysentery" definition, because it specifies low volume) but I don't think there is histological involvement of the intestinal mucosa, so there's no blood.
I'm sure the researchers worked with E. coli instead of Shigella because Shigella has such a low infective dose, and they didn't want to risk having a dysentery outbreak within their research team! It may have been better to work with Salmonella, which is a little closer to Shigella than Escherichia is. Shigella and Escherichia ARE in the same family, while they do have quite different biochemical profiles within that family.
It could also be that I have no idea what I'm talking about. I dragged out my giant binder of notes and my textbook from my medical micro class to make sure I had the characteristics of the groups of E. coli correct, but that was in 2003 so there may be new conflicting information. I still would be interested to see the effect of the brass pitchers on Vibrio cholerae, though, since that can be so devastating in areas that don't have water treatment, and it spreads throughout communities using the same contaminated water source. And I hadn't thought about heavy metal resistance - that's interesting. Can the heavy metal resistance genes be transferred on plasmids from organism to organism? I assume so, if they're located on transposons that can jump from the genome to a plasmid and back.
Thanks for the comment!
You are right about the EIEC vs ETEC. From the standpoint of bichemistry and physiology, Salmonella, Escherichia, and Shigella are basically the same bug (Salmonella has a couple of PAIs in it, I'm not that sure of the genomics of Shigella). The reason the biochemistries appear different is that we have designed many of our biochemical assays for the expressed purpose of distinguishing among the Enterobacteraceae. Anyway, interesting stuff.
Your idea about the plasmids (and transposons) is spot on. These elements pass rapidly through bacterial populations (especially if food or water borne contamination is an issue). That doesn't mean it wouldn't help, aside from the obstacles you initially cited, but it probably means any benefit would be short lived.
Yay, you came back! Thanks for the additional information.
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