Bacteriophage host range is one of the parameters needed to be considered when a bacteriophage is selected to be used as a biocontrol agent. A bacteriophage with a broad host range may not be suitable for biocontrol use because it has a tendency to be virulent to beneficial normal flora residing in human body. Therefore, before use, it has to be ensured that it is safe and cause no side effect relating to the loss of normal flora. On the other hand, a bacteriophage with a narrow inhibitory spectrum sometimes causes limitation in its use. This problem can be overcome by using a cocktail or a combination of several bacteriophages.