Fig 2.

Comparison of pre-rRNA probe pairs. Probe pairs were tested for detection of E. coli in the log and stationary phases of growth. Log- and stationary-phase cells are expected to have high and low levels of pre-rRNA, respectively, yielding a high signal ratio for log-phase versus stationary-phase cells. Probe pairs for 16S pre-rRNA had good sensitivity for log-phase cells, but the signal ratio for log-phase versus stationary-phase cells was low. Some probe pairs targeting the splice sites at the termini of mature 16S and 23S rRNA had higher signal ratios for log-phase versus stationary-phase cells. The probe pair targeting the splice site at the 3′ terminus of 23S rRNA had the best combination of sensitivity and high signal ratio of log-phase versus stationary-phase cells.