Detection of viable but non-culturable (Vbnc)‎ Escherichia coli from beef liver using Pma-PCR assay

Abstract EN

Escherichia coli, the most important foodborne pathogen worldwide, can go into a state of dormancy called viable but nonculturable (VBNC) state under various stress conditions.

Hence, it escapes detection by traditional culturing methods.

The current research made use of Propidium monoazide (PMA)-Polymerase chain reaction (PCR) assay in order to verify whether E.

coli, especially O157 strains, converted to the VBNC state under the influence of cool-warm and freeze-thaw stresses.

120 beef liver samples were collected from local markets.

The samples that were positive to pathogenic E.

coli were treated with cooling (4 °C)-warm and freezing (-18 °C)-thaw cycles to induce the VBNC state.

Samples that demonstrated the inability to form colonies on EMB agar were tested by PMA-PCR assays to confirm the existence of VBNC E.

coli.

9 samples (7.5 %) of 120 beef liver samples were positive to pathogenic E.

coli by microbiological tests.

Cool-warm and freeze-thaw stresses on the 9 samples led to the inability of 3 of them to grow on EMB agar plates.

By using PMA-PCR assay, we found that 4 °C cool-warm cycle induced E.

coli into VBNC state at a higher percentage ratio than -18 °C freeze-thaw cycle.

Even though further experiments are still required, in rare cases, at -18 °C, E.

coli VBNC may lose expression of genes responsible for viability and metabolic activity.

Additionally, our study evaluated the PMA-PCR assay as a rapid and accurate method to check for the presence of VBNC-associated foodborne E.

coli O157.