The vast majority of E. coli are what yoghurt commercials like to call "friendly bacteria", living in your gut and breaking down food into something we can absorb. True, there are a few rogue strains that engage in shenanigans and bacteriological high jinx, but overall, we owe E. coli a high five.
And this particular mutation doesn't appear to cause a problem for antibiotics (unless anyone knows of any citrate-based antibiotics in common use?); they just learned how to eat something that was previously inedible.
Sorry, maybe I should have gone in to more depth.
Some
E. Coli are harmful, some aren't, true, but not really my point. I meant that if
E. coli can evolve suddenly (in evolutionary terms) to consume a new food source previously used for categorizing them (the significance being that it was a definitive feature of their behavior and therefore useful in both diagnosis and treatment) then it is reasonable to believe that all traits can 'jump' likewise. A logical extrapolation would be that if E. coli can do it, then all bacteria can, and if E. coli can change such a notable feature then all bacteria can, and if E. coli could evolve around common forms of detection and antibiotics, then all bacteria can.
This is more than a reaction from environmental pressures being exerted on a species, this is the ability for bacteria to suddenly jump, for no observable reason, in to something remarkably different.
Also, I know this is evolution. It's been going on for millions of years, and in reality things like this happen every day, but it's still something to be cautious and conscious about.