By Karina Toledo | Agência FAPESP – Microbial resistance to antibiotics and antifungal drugs is one of the great public health problems in the world. And the solution, as a recently published study in the journal Nature Communications suggests, may lie in the small bodies of insects or, more precisely, in the microbiota they carry.
This innovative hypothesis was proposed by Brazilian and American researchers as part of a collaborative project that began in 2014, with the support of FAPESP and the National Institutes of Health (NIH) in the United States.
The idea was to isolate bacteria that live in symbiosis with leaf-cutting ants, such as saúva, in search of natural compounds with potential to give rise to new drugs ( read more in http://agencia.fapesp.br/19406).
It was with this strategy that the group coordinated by Monica Tallarico Pupo, from the School of Pharmaceutical Sciences of Ribeirão Preto (FCFRP) of the University of São Paulo (USP), and by Jon Clardy of Harvard University, discovered the cystomycin – in vitro and in vivo has been shown to kill disease-causing fungi in humans and are resistant to the drugs available today.
“It was a result that made us very happy because it corroborates our hypothesis: the insect microbiota is a promising source for the isolation of compounds with activity against bacteria and fungi. Of course, we can not say that cypomycin will become a drug, but we have made great strides and this has motivated a patent application”, Pupo told FAPESP.
As explained by the researcher, most of the antibiotics nowadays originated in compounds produced by bacteria found in soil – the majority belonging to the genus Streptomyces. The group then decided to exploit this same group of filamentous bacteria in insect bodies. The hypothesis was that if the bacterium helps the insect to defend itself against pathogens, it could do the same for humans.
“The soil has been greatly explored by the time the first antibiotics were discovered and produced. We wanted to seek a new ecological niche and we believe that evolutionary pressure would have made the insect bacteria even more effective in combating pathogens”, said Pupo.
Wide sampling
The collection work involved contributors from the United States, Costa Rica and Panama. In addition to attine tribe ants, which encompasses several genres of cutters, butterflies, wasps, bees and moths were included. Altogether there were 1,400 insects.
“In Brazil, there were more than 300 colonies of ants collected in the Cerrado, the Atlantic Forest and the Amazon. Cypermycin was isolated in a specimen of the genus Cyphomyrmex collected at the campus of USP, in Ribeirão Preto”, said Pupo.
After collection of the insects, the bacteria present in their bodies were isolated, purified in the laboratory and used in in vitro assays against pathogenic microorganisms for humans. The species that showed the greatest capacity to kill the pathogens were selected for the metabolomics studies (which allowed to characterize the metabolites produced by the microorganism and identify the most active ones) and phylogenetic ones (through the sequencing of genes indicated how isolated the bacteria of the insects were resembled their relatives on the ground).
“We combined chemometric methods and liquid chromatography coupled to mass spectrometry to trace the chemical profile of the compounds produced by the insect’s microbiota. The objective was to identify the strains of Streptomyces that produce a differentiated chemistry, that is, compounds very different from those synthesized by the soil bacteria. In this way, we increase the chances of finding a really innovative molecule”, explained Pupo.
The compounds that stood out in this more thorough selection were tested again – in vitro and in mice – against drug resistant pathogens used in the clinic.
According to Pupo, cypermycin had no action against bacteria, but was shown to be able to fight infection with Aspergillus fumigatus, a fungus most frequently found in the hospital setting and causing aspergillosis, a disease that can kill 85% of patients even after antifungal therapy .
In addition, it fights in the animals the infection by Candida glabrata and Candida auris, two species that cause candidiasis in humans also resistant to existing drugs.
“Cypermycin was not the first compound with antimicrobial action identified in our project, but no other showed this level of activity,” said Pupo.
The part of the study that uncovered the chemical profile of bacterial compounds was carried out during Humberto Enrique Ortega Dominguez‘s PhD, with support from FAPESP and Pupo’s guidance at FCFRP-USP. During a research internship at the University of Wisconsin-Madison, under the supervision of Tim Bugni and with FAPESP scholarship, Dominguez dedicated himself to metabolomic studies and isolated cypermycin, whose structural determination was finalized after his return to Brazil. Mice were also tested at the University of Wisconsin-Madison by the David Andes group, who participated in the Thematic Project.
Post-doctoral researcher Weilan Gomes da Paixão Melo, FAPESP fellowship, participated in the collection of insects, isolation and identification of the microbiota. In addition, he conducted phylogenetic studies during the research stage in Madison, in Cameron Currie’s laboratory.
The article The antimicrobial potential of Streptomyces from insect microbiomes, by Marc G. Chevrette et al, can be read at: https://www.nature.com/articles/s41467-019-08438-0