> given there's no known evolutionary pressure towards it.
There will be, once the antibiotic is put into use. And that's assuming something working roughly the same way isn't, unbeknownst to us, already present in nature, leading to countermeasures also already being present in the environment.
> Could you elaborate on how you think such a thing might appear in nature?
The same way everything else does - natural selection. By random chance, some bacteria will survive the antibiotic treatment. Those bacteria will get to reproduce where their neighbors won't. Now, while it's possible many of the survivors will be left unharmed because their mutations made them completely broken and not worth the antibiotic's metaphorical effort, eventually there will be a survivor that's mutated just right to resist while being able to reproduce and thrive. Its lineage may still die off, but then maybe next one's won't, and now you have a resistant strain in the wild, possibly further spreading resistance-conveying plasmids.
I think your explanation of how such a resistance might occur is a bit too simplified
It's a reasonable assumption that bacteria in the wild have been under pressure to increase the likelihood of developing resistance genes as an adaptation to organisms producing antibiotics in nature
This is a selective pressure that has been applied for millions of years and is likely the reason for anti-biotic resistance being able to develop independently over a relatively short timespan
With a synthetic class of antibiotics there would not have been a pressure to increase the likelihood of resistance genes developing against this particular class of drugs
As an example, soap and surface disinfectants have been in use for a long time, but to my knowledge resistance to those compounds have not develop in bacteria, despite being used much more frequently than antibiotics
There will be, once the antibiotic is put into use. And that's assuming something working roughly the same way isn't, unbeknownst to us, already present in nature, leading to countermeasures also already being present in the environment.
> Could you elaborate on how you think such a thing might appear in nature?
The same way everything else does - natural selection. By random chance, some bacteria will survive the antibiotic treatment. Those bacteria will get to reproduce where their neighbors won't. Now, while it's possible many of the survivors will be left unharmed because their mutations made them completely broken and not worth the antibiotic's metaphorical effort, eventually there will be a survivor that's mutated just right to resist while being able to reproduce and thrive. Its lineage may still die off, but then maybe next one's won't, and now you have a resistant strain in the wild, possibly further spreading resistance-conveying plasmids.