A comparison of methods for recovery of chlorine dioxide-injured Escherichia coli O157:H7 and Listeria monocytogenes Original Research Article

Direct surface-plating, overlay surface-plating and membrane-transferring surface-plating methods were evaluated for their suitability to recover uninjured and injured Escherichia coli O157:H7 and Listeria monocytogenes on green peppers after 0·1–0·5 mg l−1 chlorine dioxide (ClO2) gas for 15–30 min at 20°C under 75–80% relative humidity ClO2 gas treatments. Direct surface-plating on selective media showed the poorest recovery of injured bacteria. No significant difference (P>0·05) in recovery of injured bacteria was observed between overlay surface-plating and membrane-transferring methods. Overall, membrane-transferring surface-plating methods using tryptic soy agar (TSA) and cefixime–tellurite sorbitol–MacConkey agar (CTSMAC) (with a 2-h repair period and a 24-h total incubation at 37°C), and using TSA and modified Oxford agar (MOA) (with a 4-h repair period and a 48-h total incubation at 37°C) were the preferred methods for resuscitation of ClO2-injured E. coli O157:H7 and L. monocytogenes, respectively. Up to 5 log reductions of E. coli O157:H7 and L. monocytogenes determined by the membrane-transferring enumeration method were observed under a 0·5 mg l−1 ClO2 gas treatment for 30 min at 20°C under 80% relative humidity.