Quantitative Analysis of Houseflies-mediated Food Contamination with Bacteria

Flies play a key role as vectors in transmitting various bacteria and pose bacterial contamination risk to food. To evaluate the time- and concentration-related bacterial contamination of food by houseflies based on their attraction to the food, we determined the number of fed antimicrobial-resistant Escherichia coli transferred from houseflies to foods, sugar and milk mixture, apple, and castella (such as sponge cake). Houseflies contaminated the foods with the fed E. coli within 5 min, and the bacteria were present in high numbers on apple and castella (3.3 × 10³ and 3.5 × 10⁴ CFU/g of food, respectively). Furthermore, the number of fed E. coli on the foods increased with time, rising to 3.6 × 10⁴-1.7 × 10⁵ CFU/g. We show that the food contamination level caused by houseflies depends on the concentration of bacteria that the houseflies carry, the contact time with the food, and the attraction of the flies to the food.