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

SIMPLE SUMMARY: Staphylococcus aureus is a pathogenic microorganism of considerable importance as it is frequently involved in episodes of food poisoning due to the production of heat-resistant enterotoxins. Therefore, it becomes critically important to understand the capability of S. aureus to contaminate feed and food. Insects represent a new frontier in terms of feed and food production. The feed employed for rearing insects (called substrate) could represent one of the most important ways to involuntarily introduce risk in the production chain. Mealworms (Tenebrio molitor) represent one of the most studied insects both as feed and food. The present study assessed the ability of enterotoxigenic S. aureus strains to persist in the substrate and to produce enterotoxins in the reared Tenebrio molitor larvae. The results provide evidence of the potential risks related to the presence of this pathogen in the rearing environment. ABSTRACT: 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.