Salmonella contamination in houseflies

The impact of Salmonella on the poultry industry is not only related to animal health and public health, but also poses a problem with consequences for the international trade in poultry products and by-products, as well as for the reputation of companies. Flies can act as mechanical and biological vectors of this pathogen on poultry farms, as they have the potential to introduce and spread it within the facilities.

To study the persistence of the microorganism at different stages of fly development, an experimental contamination study was conducted using S. enteritidis (SE) on larvae, pupae, and adults of Musca domestica. Newly emerged larvae were placed in disinfected rearing containers until they reached the prepupal stage. Subsequently, 50 individuals were contaminated with an SE culture, allowing the larvae to remain in contact with a surface contaminated with the bacterium for 24 hours.

All individuals were transferred to a decontaminated environment, and 10 larvae were randomly selected. Salmonella isolation was performed using the following method: each larva was incubated individually in tetrathionate broth for 48 hours at 37 °C, then subcultured on XLD plates, and finally, the presence of colonies consistent with SE was determined. Subsequently, when the larvae reached the pupal stage (48 h after the start of the experiment) or the adult stage (at 7 days), new samples of 10 individuals each were collected for SE isolation using the methodology described above. SE was re-isolated from 80% of the larvae and 90% of the previously contaminated pupae. Furthermore, the microorganism was isolated from 16.7% of the adults.

The results demonstrate Salmonella’s ability to remain viable throughout the various developmental stages of M. domestica, even when the insects are exposed to the microorganism for only a short period of time during the initial phase. This reaffirms the importance of these insects not only in transmitting the pathogen to birds and between farms, but also in perpetuating Salmonella within facilities.

This contamination model may be useful not only for future studies on the role of flies in pathogen transmission but also for assessing the actual impact of their presence on infection levels with different Salmonella serotypes.

Keywords: Contamination, Musca domestica, Salmonella.