Behavior of inoculated Staphylococcus aureus during the rearing of Protaetia brevitarsis larvae on fermented oak sawdust as a food product.

Abstract

The increasing use of edible insects as alternative protein sources underscores the need to ensure their microbiological safety. This study evaluated the fate of Staphylococcus aureus during the rearing of Protaetia brevitarsis larvae on oak sawdust substrate inoculated with high (7 log) and low (3 log) levels of the bacterium. In the substrate, S. aureus declined rapidly and fell below the detection limit (<1 log CFU/g) within five days, regardless of initial level. Similarly, in larvae, S. aureus was detected until day 2 but not thereafter. In fasted larvae, S. aureus became undetectable from day 2, suggesting fasting may facilitate its elimination. Aerobic bacteria and coliforms were also monitored. In the substrate, total aerobic counts ranged from 8.0 to 8.3 log CFU/g at day 0, remained stable until day 10, and then decreased to 7.6 log CFU/g. In larvae, aerobic counts stayed around 7.2 log CFU/g until day 5 and then slightly increased. Coliform levels in larvae were 1-3 log CFU/g lower (3.2-5.0 log) than in substrate (5.0-8.0 logCFU/g) at day 5, but differences became negligible by day 10. These findings suggest that while externally introduced S. aureus may not persist during rearing, aerobic bacteria and coliforms remain as dominant microbial groups. Thus, post-harvest processing such as drying, freezing, or heat treatment is necessary to ensure the microbial safety of P. brevitarsis larvae for human consumption.