Effect of filtered volume of ASW on the sensitivity of vvhA mRNA detection, using seminested RT-PCR. Shown are results from 11-day-old VBNC cells of clinical strain C7184. Lanes: 1 and 2, RNA extract from duplicate 5-ml samples; 3 and 4, RNA extract from 25-ml duplicate samples; 5 and 6, RNA extract from 50-ml duplicate samples; M, 100-bp DNA ladder size marker (Life Technologies); +, positive control with RNA extracted from a stationary-phase culture of strain C7184; −, negative control without RNA.