Now I've heard a convincing story, courtesy of The Loom. The lethal toxins are produced by viruses, and bacterial death by antimicrobials unleases the viruses:
The Loom : Why Tainted Spinach And Antibiotics Are a Bad MatchOur GI immune system has presumably evolved to kill the bacteria without triggering release of the viruses. A tricky and complex maneuver. Antimicrobials are less discriminating.
Like other microbes, Escherichia coli O157:H7 carries a number genes that were delivered to it by viruses. In some cases, the viral DNA has mutated to the point that it cannot produce new viruses, and so the genes can only be passed down from one generation to the next. In other cases, the viruses are dormant but still independent. In response to stress, Escherichia coli starts making new copies of the virus, which then burst out of their host. Antibiotics are among the stresses that trigger the viruses to escape. It's a good strategy for the virus, because it can escape from its host before the antibiotics kill the bug. It's not so good for the host [jf: the bacteria], of course, and can be pretty bad for us as well. That's because the toxins in Escherichia coli that can cause organ failure are actually carried by the viruses. The genes only become active as the host begins making new viruses. That means that if you take antibiotics for infection with Escherichia coli O157:H7, you may wipe out the infection, but you may also trigger organ failure...
Hmmm. Multiple-system organ failure and sepsis must be imagined rather differently now than it was back in the day. Doubtless reasearchers have been looking for similar viral payloads in a wide range of infections. The trick may be to slow bacterial replication without stressing the viruses too much, so that the human immune system can survive long enough for a quieter means of bacterial assassination.
PS. Speaking of The Loom, I think of it and about 70 of my other favored blogs everytime I read about how the blogosphere is full of blather and nonsense. Such claims are so absurd that, on reading them, I not only turn the article aside I put the author into a metaphorical trashbin.