Behaviour of Staphylococcus aureus in the Rearing Substrate of Tenebrio molitor Larvae

Tenebrio molitor (mealworm) is one of the most promising insect species to produce sustainable feed and food with high nutritional value. Insects may harbour microorganisms both in the gut and on the exoskeleton originating from the rearing environment. Staphylococcus aureus is a pathogenic microorganism frequently involved in food poisoning due to its enterotoxin production. This study aimed to evaluate the S. aureus growth and enterotoxins production following an experimental inoculation into the T. molitor rearing substrate (about 7 log CFU/g). Analyses on the substrate and larvae were performed over a testing period of seven days. The microbial population dynamics were also evaluated through total viable count and lactic acid bacteria count. The effects of fasting, washing, and cooking on the microbial loads of mealworms were evaluated. The results highlighted that mealworms and substrates can maintain their microbial loads of S. aureus over the tested period. Moreover, fasting and washing were generally not able to significantly reduce (p-value > 0.05) S. aureus count in mealworms. On the other hand, cooking significantly reduced (p-value < 0.001) the microbial load in almost all cases. No production of enterotoxins was revealed during the trial. Therefore, microbiological risks can be reduced by a wise choice of substrate, appropriate control measures, and thermal treatment of larvae.