Honestly you're just amplifying my point. Why is this the case? Edit - Actually, maybe not. Let me give this a shot - just to do napkin math again. 1 Staphy

Honestly you're just amplifying my point. Why is this the case? Edit - Actually, maybe not. Let me give this a shot - just to do napkin math again. 1 Staphylococcus aureus is ~1um in diameter or ~5e-15 liters in volume. They reproduce let's say once per hour, so if you had a liter of them after an hour you would have (1 / 5e-15) * 2^24 or 3.3e21 reproduction events. Let's say immunity is transferred at a specific spot in the DNA, first three nucleotides in gene X are flipped to ACT. Spontaneous DNA replication errors happen roughly between every 10e5 and 10e9 replication events. Staphylococcus aureus has ~2.8M base pairs and we need to set a specific three of them to ACT. My stats are a little rusty but the likelihood of any error happening on the low end is 1:10e5. The likelihood that this error occurs in the right spot while still leaving a viable organism has to be greater than 1:2.8e6 but not 1:1 or you're just spitting out random shit. Let's cut it to 1:1e5. The likelihood that the output of three base pairs being ACT under random chance is 3^4 or 81. All of these together i'm getting ~8e12. So i'm being pretty generous here but the likelihood that you'll get a resistant strain would then be ~1:8e12. With 3.3e21 replication events that gives you almost 2 billion resistant bacteria over 24 hours. Moving to more reasonable values you start with 10µL of staph, spontaneous replication errors every ten million splits and let's split the chance of the mutation being in the right area to 5e5. You end up with 3.3e16 replication events and roughly 1:4e15 chance of getting a resistant mutation or approximately 20 resistant bacteria after 24 hours. Still enough to get the party started. So maybe this case is a little different?