Contamination of Zophobas morio Larvae Rearing Substrate with Listeria monocytogenes: A Preliminary Study

SIMPLE SUMMARY: Over the past 20 years, we have seen exponential growth in the number of scientific publications on edible insects as an alternative food source. Usually, insect larvae are reared in a close environment in constant contact with their feed, called the substrate. The substrates employed for rearing could represent one of the most important ways to involuntarily introduce risk in the production chain. In this research, we inoculated one of the most important food pathogens, Listeria monocytogenes, in the substrates used in Zophobas morio rearing (also called superworm). The results highlighted the caution needed in insects rearing and the potential risk related to this pathogen in relation to superworm rearing. Attention was also focused on the technological procedure employed in insect rearing and processing. ABSTRACT: The interest in edible insects is continuously increasing due to their environmental, nutritional, and productive features. The aim of this study was to evaluate the effects and survival of Listeria monocytogenes in Zophobas morio rearing, using two different bacterial loads (2 and 6 log CFU/g). We also considered the effect of washing, fasting, and cooking treatments on the larvae. During the experimental trial, no mortality was observed among the larvae. The L. monocytogenes loads decreased over time, and it was below the detection limit for crates inoculated with 2 log CFU/g, while the substrate inoculated with 6 log CFU/g reached loads of 4.26 (without larvae) and 2.83 log CFU/g (with larvae). Due to the absence of L. monocytogenes in the larvae on day seven, it was not possible to assess the fasting treatment or the washing and the cooking. However, when looking at the total microbial count, significant effects were revealed for all treatments. The unfasted larvae showed no effect of washing, while the total microbial counts decreased after washing in the fasted larvae. This proves that fasting is a good treatment in terms of hygiene assurance for the consumer.