Mitochondrial nucleic acid depletion and detection

A method for depleting host nucleic acid in a biological sample, said sample having been previously obtained from an animal host and having been subjected to treatment to lyse host cells present within the sample, said treatment to lyse host cells being a treatment with a cytolysin, and wherein said sample has been subjected to a treatment to deplete nucleic acid released from host cells within said sample or otherwise to render such nucleic acid unidentifiable, the method comprising:

• (a) depleting host mitochondria or host mitochondrial deoxyribonucleic acid (mtDNA) present in the treated sample;
• and
• (b) extracting and/or analysing remaining nucleic acid from the treated sample;
• wherein step (a) comprises:
• (i) adding a detergent to said treated sample;
• (ii) at least partial removal of host mitochondria by contacting the treated sample with an immobilised binding agent that selectively binds mitochondria;
• or
• (iii) extraction of whole nucleic acids and further capture of mitochondrial DNA using a panel of DNA and/or RNA and/or PNA baits that target the host mitochondrial genome;
• and
• wherein step (a) further comprises adding a nuclease to said treated sample.