Study sheds new light on antibiotic resistance gene transfer between bacteria

February 19, 2019

By studying aquaculture-raised fish, researchers at the Helmholtz Zentrum München, the University of Copenhagen and the University of Campinas in Brazil shed new light on the mechanisms by which genes for antibiotic resistance are transferred between bacteria. According to the study published in the journal Microbiome, these mechanisms are more varied than previously thought.

Piaractus mesopotamicus, a South American species known as pacu, is often raised in aquaculture. © Helmholtz Zentrum München

"Over the last 70 years, the use of antibiotics in human and veterinary medicine has steadily increased, resulting in a dramatic increase in the number of resistant microorganisms," says Professor Michael Schloter, head of the department. Microbiome Comparative Analysis Research Unit (COMI). at the Helmholtz Zentrum München. It is particularly alarming to note that many microorganisms are resistant not only to an antibiotic, but to a whole range of different substances, said the corresponding author of the recent study. This poses particular problems in the treatment of infectious diseases. "We have therefore undertaken to discover the mechanisms responsible for the development of resistance," he said.

To this end, he and his team, along with Danish scientists led by Gisle Vestergaard (University of Copenhagen and Helmholtz Zentrum München), investigated fish raised in aquaculture. More specifically, they studied Piaractus mesopotamicus, a South American species known as pacu, is often raised in aquaculture. The fish received the antibiotic florfenicol in their food for 34 days. During this period and after the period of application, the researchers took samples from the digestive tract of the fish and searched for relevant genetic modifications in intestinal bacteria.

Resistance genes go around the genome

As could be expected, the administration of the antibiotic resulted in an increase in genes responsible for resistance to this antibiotic. An example is the pump protein genes, which simply remove the active substance from the bacteria again. However, we were particularly surprised by the different mechanisms that we have been able to detect by which antibiotic resistance genes are spreading among intestinal bacteria in fish. This suggests that bacteria also exchange resistance through viruses, called phages, and transposons. "

Johan Sebastian Sáenz Medina, COMI PhD student, Lead author of the document

Other metagenomic studies have confirmed that these mobile genetic elements induce a rapid distribution of resistance genes between the genomes of different organisms. Until now, it has been postulated that only plasmids (essentially easily transferable mini-chromosomes) are primarily responsible for the exchange of resistance genes.

The discovery that resistance is also widely transferred between bacteria without plasmid involvement is really very surprising. On the basis of this observation, the relevant dissemination models should be examined and modified. In addition, our data certainly leads us to question whether and to what extent we should continue to use antibiotics in the growing number of aquacultures around the world. "

Dr. Michael Schloter, Head of the Microbiome Comparative Analyzes Research Unit (COMI) at Helmholtz Zentrum München