It's rare to need an antibiotic unless you allow water to remain in your fuel, unless the weather is warm and unless the car is not used regularly. Bugs essentially "live" in water that's in the fuel (water condenses out of any air in the tank EVERY time the temperature drops below the dew point of the air - good reason to keep the tank FULL or neasr full of fuel when the temps are expected to drop or when the car is NOT being operated daily) and eat the fuel. If you keep the levels of water in the fuel low and actively remove it (by using an antigel or other additive that sequesters water) once or twice a year (I do it in the fall and then whenever I expect temps to go much below zero F) and use clean fuel, there is rarely a problem. I have not had ANY problem with "bugs" in more than 20 years (I've been dieseling for 35).

Farm and marine engines that are not used for long periods should probably be treated, but an automobile that driven regularly, fed clean fuel and maintained shouldn't require it.

Marshall