As soon as I first saw this book, I said "That's the best idea ever!" and indeed, reading it has not disappointed me. It's a guide, organized by type of bacteria, to how to recognize their presence around you by macroscopic signs such as colors, slimes, and especially smells. The author is an excellent writer (I also recommend her Tracing the History of Eukaryotic Cells: The Enigmatic Smile), and this book is just plain entertaining to read from cover to cover. I'll never see my stinky dishwashing sponge the same way again.