RIBOSOMAL-RNA STABILITY IN HEAT-KILLED AND UV-IRRADIATED ENTEROTOXIGENIC STAPHYLOCOCCUS-AUREUS AND ESCHERICHIA-COLI O157-H7

Differentiation of viable cells from nonviable cells is of considerabl e importance in the development of methods to detect foodborne pathoge ns, To study the suitability of 16S rRNA as an indicator of cell viabi lity in nucleic acid-based detection assays, we examined rRNA stabilit y in two representative foodborne pathogens, Escherichia coli O157:H7 and enterotoxigenic Staphylococcus aureus, which mere inactivated by e xtreme heat, moderate heat, and UV irradiation. Cell death under all c onditions was confirmed by a failure to grow in brain heart infusion b roth after incubation for 48 h at 37 degrees C. rRNA stability was mon itored by a Northern blot analysis, and detection was evaluated by usi ng reverse transcription (RT)-PCR performed with two primer sets (whic h produced 325- and 1,400-bp amplicons). rRNA of neither pathogen was detected by Northern blot analysis and RT-PCR after cells mere killed by autoclaving at 121 degrees C for 15 min. in contrast, intact rRNA o f both pathogens were detected by Northern blotting and could be ampli fied by RT-PCR up to 48 h after cells were killed by heat treatment at 80 degrees C and UV irradiation at 254 nm, rRNA was a suitable target molecule for monitoring bacterial viability under extreme heat condit ions, but the presence of rRNA was not correlated with viability follo wing moderate heat inactivation or UV irradiation of cells.