Who is hitching a ride on the house fly?

8 November 2019
A team of researchers from the VIB-KU Leuven Center for Microbiology found that house flies are real taxi’s for microbes.  And, they do not care much about which passengers they are taking along for the ride.  Bacteria, fungi and even pathogenic microbes are all transported on the flies’ bodies.  Inside the flies, however, the diversity of microbes is lower, suggesting that only specific microbes survive. The findings will be published in BMC Microbiome.

A fly’s passengers
It’s a sunny summer day and you are having a garden party. A fat black house fly comes on your plate and walks around on your food for a few seconds. Would you still eat it? Rahel Park (VIB-KU Leuven Center for Microbiology) took an in-depth look at the microbes carried by the house flies, and those residing inside their bodies. 

She identified specific microbial patterns linked to the origin of the flies. Overall, the portion of the potentially pathogenic microbes is low in the total microbial community. However, in a microbe-rich environment, flies readily pick up microbes, making the flies active vectors of pathogens during a disease outbreak.

Catching flies and identifying microbes
House flies prefer to live close to humans, hovering around decaying matter, garbage, and feces as well as human food. They are spread worldwide and have been shown to carry microbes, including some that cause disease. However, despite the prevalence of house flies, a comprehensive picture of their role as taxi’s for microbes was still lacking.  To get an in-depth picture, the research team sampled over 400 flies from Belgium and Rwanda and from three different environments – cow farms, homes and hospitals. 
“It was quite an interesting sampling effort”, says Rahel Park, the lead author of the paper. “We had to capture each fly individually, while avoiding a kick from the cow, and then transport them back to the laboratory – in the case of Rwanda in an ice box behind the motorbike taxi. After that, we investigated the bacteria and fungi present inside and on the outer surface of these flies using the latest DNA sequencing technologies”.

Inside and outside
“The results show that the overall patterns of bacteria found inside the flies are relatively similar between flies from different countries and habitats, suggesting that, as is the case in humans, the species of microbes that live inside the flies are specifically attuned to living there. The flies’ outer surface, however, showed an entirely different picture and harbored an enormous variety of microbes,” says prof. Kevin Verstrepen, who led the research effort in collaboration with prof. Jeroen Raes (both from the VIB-KU Leuven Center for Microbiology) and prof. Bart Lievens (KU Leuven Department of Microbial and Molecular Systems).

Prof. Verstrepen continues: “Interestingly, flies isolated from similar niches carried more similar microbial communities, indicating that microbes from the environment are easily picked up on the outer surface of the flies, especially in habitats rich in decaying and fecal matter, such as farms. For fungi, both the internal and external communities varied with country and habitat, suggesting that fungi are mostly hitchhikers rather than long-term residents.” 

This study reinforces the idea that during disease outbreaks, when pathogens are prevalent, house flies can be important carriers of potentially harmful microbes.

Publication
 
Finance
Work in the laboratory of prof. Kevin Verstrepen is supported by VIB, KU Leuven, FWO, VLAIO, and European Research Council (ERC) Consolidator Grant CoG682009

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 Rahel Park