I did a small experiment as part of my larger research project. I wanted to find out how many different bacterial species were living in my saliva. In our lab we look at the bacteria in human samples all the time, so I decided to include my own saliva in one of these test runs. One morning I spat in a tube several times, until I had spat around 5 milliliters, and then capped it and took it to work. I spat before I had brushed my teeth, hoping to get the maximum number of bacterial species. At work I extracted DNA from this saliva sample and then ran it through our handy dandy DNA sequencer to see what was in there. (Identifying bacteria by sequencing DNA is very common these days. I'll write more about this later.) I also used some of this DNA to test some purification methods our laboratory is trying to develop, so it wasn't a completely selfish exercise.
Lo and behold, when the results were in, I was surprised to find out how much diversity was present in my mouth. I am still analyzing the data, and will write more about it later, but I will tell you that there were probably hundreds of bacterial species present in my saliva sample. Scientists have known for a long time that bacteria are abundant in saliva. After all, bacterial biofilms are what constitute plaque. But I was very surprised to learn that the number of species was so high. Now there are some difficulties defining what a species is in bacteria (I'll write more about this later too), but suffice it to say, hundreds of bacteria are calling my mouth home.
