Is food poisoning possibly salmonella dangerous to a unborn baby in the first trimester?

Yes. Listeria is the really bad bug. It is medically proven to cause miscarriage. That is why you are warned against eating semi re-heated food and soft cheeses. If you have a bout of food poisoning, you risk miscarriage within the next 24 hours. If it has been more than 24 hours, you should be okay. There is no risk to the baby (ie developmental) otherwise. If your baby is still okay after 24 hours, you will both be fine.