A method for testing for target Mycobacteria in a reaction mixture comprising the steps of: providing a reaction mixture; admixing a bacteriophage with the reaction mixture under conditions suitable to allow the bacteriophage to infect any target Mycobacteria present in the reaction mixture; allowing time for the bacteriophage to lyse infected live target Mycobacteria; and analysing in said reaction mixture DNA from the lysed Mycobacteria to identify a signature DNA sequence that occurs in the target Mycobacteriumspedes.