A natural E. coli RNA MS2 coliphage [28] (MS2, ATCC 15597-B1) stock was prepared on E. coli Top 10F in NZYCM broth as described by Dreier et al [5] . Aliquots of the stock were frozen at 270uC. The concentrated stock was thawed, serially diluted in dilution buffer [100 mM NaCl, 8 mM MgSO 4 , 50 mM Tris pH 7.5 and 0.01% (w/v) gelatin] and added to the respective extraction lysis buffers used in each of the extraction procedures before use. The amount of external control MS2 template added to the lysis buffers was adjusted to give a Ct of approximately 27 (,10,000 copies/ml) in the rRT-PCR mix upon addition of 5 ml of RNA.