We have had outbreaks of such micro-organisms in British hospitals recently and there was the horrific outbreak of foot and mouth disease that led to funeral pyres of dead animals not so very many years ago.
I'm no expert microbiologist but.....
We've had outbreaks of fatal infection by such micro-organisms for the whole of human history though. We're just lucky that recent times (the last century or so) have seen the availability of antibiotics to treat such infections. But you could say we have, unwittingly, encouraged the micro-organisms involved to evolve perhaps on a quicker timescale than previously by increasing the environmental pressure (the use of antibiotics) on them to do so leading to antibiotic resistance.
Bacteria and viri will always evolve: their relatively simple genome and rapid rate of multiplication ensures that mutations will always occur, and that a small resistant population resulting from such a mutation will increase in number quickly because the non-resistant population has died out leaving something of a vacuum to be filled. If we don't have any more weapons (i.e., new antibiotics) in our armoury then the number of untreatable fatal cases is likely to increase until we find something to treat it.
Take MRSA: the clue's in the name, Methycillin Resistant Staphylococcus Aureus - just one group of strains of Staph aureus, a very common microorganism that is found everywhere, including up everyone's nose. Now that those harmful strains of the organism have evolved to be resistant to the last group of antibiotics capable of preventing its growth (including Methycillin) due to environmental pressure, we no longer have anything to treat it. MRSA has not been caused by our hospitals being dirtier, it's been caused by the organism evolving; that's not to say that hygiene in hospitals doesn't have a place in preventing its spread - hand washing, patient screening, barrier nursing etc.
Which is what is frustrating about the hyperbolic media coverage (willingly so probably, a good scare story sells papers) of such outbreaks: the Mail printing the word MUTANT in massive letters on their front page for example. They make it sound like Staphylococcus aureus or Escherichia coli have until now been benign, cuddly organisms that have suddenly mutated into snarling, teeth-gnashing monsters. But these mutations are nothing new, it's just that recently the development of new treatments has been overtaken by the pace of evolution of the organisms.
Foot and mouth evolves in a similar way, which makes developing a vaccination difficult - a vaccine has to target each individual strain, of which there are more than one. But the risk of a human contracting FMD is minimal and even in infected animals it is only fatal in a small number of cases (although an infection is painful for the animals concerned); the main effect is to decrease growth and milk production (usually permanently, even if the animal recovers). The case for dealing with FMD outbreaks in the way we have seen recently is largely an economic one.
Here's a good overview of bacterial/viral evolution:
http://www.bacteriamuseum.org/cms/Evolution/evolution-in-bacteria.html
