Blowflies carry a high percentage of bacteria that cause diseases in humans

A study has found that 30% of the microorganisms found in these insects cause diseases such as bubonic plague, gastritis, ulcers and stomach cancer.

By Karina Toledo, in Campinas

Agência FAPESP – Nearly 30% of the microorganisms found in blowflies are capable of causing diseases in humans says a study carried out by researchers at the University of Campinas (Unicamp), Pennsylvania State University in the United States and Nanyang Technological University in Singapore.

Among the bacteria found in the bodies of the insects were Yersinia pestis, which causes bubonic plague, Helicobacter pylori, which is associated with gastritis, ulcers and stomach cancer, and several species that can cause gastroenteritis, pneumonia and urinary infections.

The data were presented by Ana Carolina Martins Junqueira, a researcher at the Singapore Center on Environmental Life Sciences Engineering (Scelse) in Singapore, during the event “Advanced Topics in Genomics and Cell Biology,” held August 4-6, 2014, at Unicamp.

“Everyone knows that flies are dirty insects, but the rate of pathogenic bacteria was so high that we were stunned. It’s the most pathogenic microbiome ever described. We’re going to now begin some experiments to determine whether flies merely transport the microorganisms or whether they in fact transmit these diseases to people by landing on food, for example,” Junqueira explained.

The scientists analyzed the microbiota found in the bodies of 127 flies from 19 species that are usually attracted to decomposing organic matter. The insects were collected in 12 different locations in the U.S. and Brazil during Junqueira’s post-doctoral studies, sponsored by FAPESP and carried out at Unicamp.

In the areas around Campinas, collections were performed at a public hospital, a food market, a city park and a rubbish dump. Collections were also made at a nature reserve in the Amazon Forest and in six stalls of different species of animals raised on the Penn State University Park campus, in State College, Pennsylvania. A control lineage was maintained in a laboratory at the Center for Molecular Biology and Genetic Engineering (CBMEG/Unicamp).

Junqueira remarked that the original project goal had been to sequence the mitochondrial genome of 20 species of flies belonging to the order Diptera as well as to study the evolution of these insects with the help of next-generation sequencing platforms.

“In the beginning, I had some trouble sequencing certain fragments of the genome. Then, I met Stephan Schuster, at the time a professor at Penn State University, who became interested in the work and decided to collaborate,” said Junqueira.

Schuster suggested that the best way to map the mitochondrial genome would be to sequence everything from the collected flies, including the microbiota they carried, and then to filter the associated genomes (metagenome) during the data analysis step. “First we sequenced only the head, then the thorax and abdomen and, finally, the feet and wings,” the researcher explained.

After completing her post-doctorate, Junqueira worked with Schuster in the United States to analyze the metagenome. To do that, they needed to develop new techniques to optimize the treatment and categorization of the immense volume of data generated by next-generation sequencing methods.

“By using statistical analyses on the microorganisms collected, it was possible to separate the flies according to where they were found: urban environments, the Amazon, rural environments and the laboratory. This shows that the environment has much more impact on modulating the microbiome than the species itself,” Junqueira said.

According to the researcher, the number of pathogens found in the flies from urban environments was much larger than from the other environments, likely because there is more trash and decomposing organic matter available in that environment.

“The real problem is that these insects easily go back and forth between a filthy environment such as a dump and, for example, our backyard barbeques. In the flies collected inside the hospital, we found bacteria responsible for two-thirds of the world’s hospital infections,” Junqueira commented.

In addition to the fact that the bacteria are pathogenic to humans, the researcher added, species that can cause diseases in plants and animals were also found.

“We defended the hypothesis that this type of insect can be used as an environmental sensor to help predict outbreaks, mainly in border areas, ports and airports. We could monitor contamination by analyzing the microbiome of these flies,” the researcher said.

Aedes

At the Singapore Center on Environmental Life Sciences Engineering, Schuster and Junqueira are currently using the same approach created in the study of blowflies to investigate the microbiome of Aedes aegypti, the mosquito that can transmit dengue.

“The goal is to see whether there is a difference between the microorganisms found in mosquitoes infected by the dengue virus and those not infected. The study is still in its early stages and, for now, we’ve only worked with laboratory specimens. However, we have already observed differences between the bacteria found in these two groups,” Junqueira explained.

In the future, the scientists are planning to investigate the possibility of preventing the mosquitoes from being infected with the virus through modulation of the microbiome found in their bodies.

At the same time, Junqueira is also working with researchers from the Center for Molecular Biology and Genetic Engineering (CBMEG/Unicamp) led by professor Ana Maria Lima de Azeredo-Espin. With support from FAPESP, the group is analyzing microRNAs of different species of blowflies and livestock pests to attempt to understand the regulation of genes involved in the feeding habits of these insects.

“The study could generate data on the genetic factors of flies that are associated with their attraction to decomposing organic matter or live tissue, in addition to providing essential data for the study of the host-microbiome interaction,” Junqueira explained.