Yes lemon juice does kill bacteria in your mouth.
Lemon juice contains citric acid which contains antibacterial properties which can kill off the bacteria in your mouth.
The lemon juice is also healthy for you so you get other health benefits as well as killing bacteria in your mouth.
I love to drink a glass of lemon juice in the summer and not just lemonade but actual lemon juice as well.
However the citric acid can damage your teeth enamel if you don't brush your teeth often enough after drinking lemon juice.
But the lemon juice is good to drink on a daily basis to keep bacteria out of your mouth and the Lemon Juice contains vitamins which can possibly prevent cancer and boost your bodies immune system which could help prevent colds and flu viruses.