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In other words, there is a relatively high likelihood that a particular mutation in a target sequence will result in antibiotic resistance.
This high likelihood translates into a very rapid evolutionary process. The evolution of antibiotic resistance of any previously susceptible bacterial colony to just about any antibiotic is usually realized within a very short period of sustained antibiotic exposure.
Take for instance penicillin resistance in Staphylococcus bacteria.
This requires the bacterium to have DNA information coding for production of a complicated enzyme (penicillinase), which specifically destroys penicillin.
The same limitations seem to be present when it comes other functions that exist at a similar level of functional complexity (i.e., having a similar minimum sequence size and specificity of amino acid residue arrangement for a minimal degree of selectable function).
This might be a very good clue to the existence of a real evolutionary pathway, but not necessarily.
When a large number of bacteria are presented for the first time with an antibiotic, most, if not all of them, die off.
If all of them die, then obviously no resistance is gained for that particular bacterial colony or group.
As additional support for this statement, consider that bacteria recovered from historical isolation have been found to be resistant to modern antibiotics.
The de novo evolution of antibiotic resistance is based on the specificity of antibiotic interactions with various protein sequences within a bacterium.
Because of the specificity of such interactions, a very high ratio of mutations are able to interfere with or completely disrupt these specific interactions - and antibiotic resistance is the result.
It is extremely unlikely that such complex information could arise in a single mutation step, and in fact it does not.
Mutation can cause the loss of control of its production, so much greater amounts are produced, and a bacterium producing large quantities of penicillinase will survive when placed in a solution containing penicillin, whereas those producing lesser amounts will not.
So called "Superbugs" are springing up everywhere that are resistant to every antibiotic or antiviral currently known to man.