Don't worry about bacteria! There are bacteria everywhere. Soil is full of bacteria - many that can kill you if you didn't have an immune system. This should actually make you feel safer than not - as you were just fine gardening and playing in the garden all your life. But, yes, nitrogen burning is the issue. Chicken and Duck poop are highly nitrogenous. You can add some fresh, but not a lot. A month could help - especially if you mix it in and add some brown organic matter too - like chopped leaves or dried grass (non-treated with herbicides), straw, spoiled hay (without weed seeds) etc. Get a compost system going though and use that in the future. You can use a little dried uncomposted manure occasionally as a boost for high-nitrogen using plants, but be judicious.