EFFECT OF STRESS TREATMENTS ON THE DETECTION OF LISTERIA-MONOCYTOGENES AND ENTEROTOXIGENIC ESCHERICHIA-COLI BY THE POLYMERASE CHAIN-REACTION

The relationship between viability assessed by plate counts and detect ability by gene probe-polymerase chain reaction (PCR) techniques was e xamined with cells of Escherichia coli and Listeria monocytogenes prev iously exposed to a range of stress treatments. In all cases the organ isms were detectable by PCR after plate counts had declined to zero. T reatment with acid or hydrogen peroxide caused loss of PCR soon after viability was lost, but strong PCR signals were obtained from starved or desiccated cells long after cells became non-viable. Exposure to te mperatures up to 100 degrees C had little effect on detection by PCR a nd even autoclaving cells at 121 degrees C for 15 min failed to abolis h PCR detection completely. There is thus no simple relationship betwe en viability and detectability by PCR. Detection of pathogens by PCR i n environmental monitoring requires additional evidence of viability b efore risk can be properly assessed.