Comparison of direct PCR and PCR amplification after DNA extraction for the detection of viable enterotoxigenic Escherichia coli in laboratory microcosms

Abstract

Studies of laboratory microcosms have shown that enterotoxigenic Escherichia coli (ETEC) lose their culturability but remain viable when exposed to starvation conditions. A polymerase chain reaction (PCR) procedure was used to detect viable cells incubated in artificial seawater microcosms, either directly after boiling the water or after extracting the DNA. After 4 days of incubation, culturable bacterial counts decreased to < 1 CFU ml −1 but viable bacteria were detected for up to 6 days in all cases. After 15 days, only direct PCR remained positive and after 21 days, all results were negative. The non-culturable state of ETEC may pose health problems, and this study demonstrated the efficiency of direct PCR to detect total viable starved Escherichia coli strains.