Systematic review of the microbiological status of farmed and processed Tenebrio molitor: Insights on foodborne pathogens in food and feed applications

Edible insects are gaining recognition as a sustainable, protein-rich source of food and feed, with microbiological food safety being a critical consideration, especially regarding potential foodborne pathogens. Tenebrio molitor (yellow mealworm) is a key candidate to be introduced into food and feed, as it is already widely farmed and consumed in Western countries. This systematic review aimed to identify and evaluate studies investigating the microbiological profile and occurrence of biological hazards in farmed and processed mealworms. A comprehensive search in January 2024 resulted in the inclusion of 64 studies employing both culture-dependent and independent methods. Quantitative microbial data was synthesized, and the quality of integrated studies was assessed based on key factors relevant to microbial analysis of insects. Results indicated high levels of microbial indicators (e.g., total viable count, Enterobacteriaceae etc.) in raw mealworms, although common foodborne pathogens such as Salmonella spp., Listeria monocytogenes, and pathogenic Escherichia coli were rarely detected. Major safety concerns included Staphylococcus aureus and spore-forming bacteria, notably Bacillus cereus group and Clostridium spp. (e.g., C. perfringens and C. botulinum). Several opportunistic and emerging bacterial pathogens were also identified, though studies on fungi, viruses and parasites remain limited. While rearing conditions (e.g., substrates), post-harvest measures (e.g., fasting, rinsing, killing), drying, packaging, storage and other innovative processes can affect microbial loads to some extent, heat treatment remains the primary inactivation method. This review underlines the need for more comprehensive microbiological data on T. molitor and other insects, to establish effective risk mitigating measures.