Survival of Listeria monocytogenes on growing and harvested Trumpet Royale (Pleurotus eryngii), Alba Clamshell (Hypsizygus tessellatus), and Brown Clamshell (Hypsizygus tessellatus) mushrooms

Abstract

Outbreaks and recalls of Listeria monocytogenes associated with commercial mushrooms have been reported in recent years. Unfortunately, knowledge about the survival of L. monocytogenes on different mushrooms remains limited. This study aims to characterize the survival of L. monocytogenes on growing and harvested Trumpet Royale (Pleurotus eryngii), Alba Clamshell (Hypsizygus tessellatus), and Brown Clamshell (Hypsizygus tessellatus) mushrooms. Mushrooms were spot-inoculated with rifampin-resistant cocktails of L. monocytogenes on the caps with an initial level of ca. 8 and 4 log CFU/mushroom and air-dried for 30 min until no visible inoculum was observed on the inoculated area. The survival of L. monocytogenes was monitored on growing and harvested mushrooms for up to 7 days after inoculation. L. monocytogenes inoculated on growing mushrooms dropped below the limit of detection after day 2 or day 3 regardless of the inoculation levels. L. monocytogenes persisted on harvested mushrooms for up to 7 days regardless of mushroom types and inoculation levels at 4 °C. By the end of 7-day storage, 6.1, 3.8, and 6.2 log CFU/mushroom of L. monocytogenes were recovered from Trumpet Royale, Alba Clamshell, and Brown Clamshell, respectively (inoculation level: ca. 8 log CFU/mushroom). At low inoculation levels (ca. 4 log CFU/mushroom), L. monocytogenes positive samples were found in all types of mushrooms after 7-day storage. The results of this study highlight one key important finding, that is the behavior of L. monocytogenes is significantly different between growing mushrooms and harvested mushrooms. Such information is critical for the development of food safety plans for the mushroom industry from pre-harvest to post-harvest stages.