My thoughts exactly. I'd speculate that they're saying that all bacteria had some resistance to start with, rather than the various types of bacteria all havin

My thoughts exactly. I'd speculate that they're saying that all bacteria had some resistance to start with, rather than the various types of bacteria all having mutated to have this characteristic. The implication being that if a large number of bacteria were already immune then evolution favouring this immunity requires a lower rate of evolution to if that characteristic was a recent mutation which then immediately became favoured and spread; as each mutation having any success would be less likely, and therefore implying that this is such a significantly beneficial mutation (given human use of antibiotics) that evolution has favoured this attribute far more than otherwise would have been required.