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

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 and Listeria monocytogenes on green peppers after 0.1-0.5mg l(-1) chlorine dioxide (CLO2) gas for 15-30 min at 20degreesC 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 37degreesC), and using TSA and modified Oxford agar (MOA) (with a 4-h repair period and a 48-h total incubation at 37degreesC) 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 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 20degreesC under 80% relative humidity. (C) 2002 Elsevier Science Ltd. All rights reserved.