When you asked this the first time, I thought it was simply a shorthand question because you didn't want to go into details. Now it seems more likely that you are mixed up about some of these concepts, as you are asking about something that doesn't really happen in real life.
First, biologists are rarely making antibiotics - most of them are natural products that may be slightly modified, and mostly by chemists. Bacteria and fungi make antibiotics as a way of competing with each other, so they actually kill microorganisms rather than making them resistant to certain diseases. Again, we co-opted this killing property of natural products for our own benefit.
As to predicting resistance from bacterial sequence, for most antibiotics we know how they kill bacteria, and for many of them we know how bacteria develop resistance. Without getting into the weeds, in most cases they are proteins that either: 1) modify or break down the antibiotics; 2) modify its target molecule so it has no substrate to work on; 3) pump the antibiotic out of the cell. Those proteins are of known sequence and often of known structure, so one can look for them in bacterial genomes (and plasmids) and predict whether these organisms are likely to be resistant.