February 26, 2019


Study finds mechanisms for transfer of antibiotic resistance to be more varied



In a study that examined aquaculture fish, researchers had confirmed that the use of antibiotics prompted a rise in genes responsible for resistance to the antibiotic used.  


The research team, comprising of members from Helmholtz Zentrum München, the University of Copenhagen and the University of Campinas in Brazil, discovered that mechanisms, by which antibiotic resistance genes are transferred between bacteria, are more varied than previously thought. 


"In the past 70 years, the use of antibiotics in human and veterinary medicine has steadily increased, leading to a dramatic rise in resistant microorganisms," said Prof. Dr. Michael Schloter, head of the research unit for Comparative Microbiome Analyses (COMI) at Helmholtz Zentrum München and the author of the study.


However, what is startling is that several micro-organisms are resistant to an array of substances, not just one antibiotic, according to Dr. Schloter. This discovery prompted the researchers to seek out the mechanisms that facilitate resistance development, he said. 


Dr. Schloter and his team, together with Danish scientists led by Gisle Vestergaard (University of Copenhagen and Helmholtz Zentrum München), investigated fish raised in aquaculture.

Specifically, they studied Piaractus mesopotamicus, a South American species known as pacu that is often raised in aquaculture. The fish received the antibiotic florfenicol in their food for 34 days. During this time and after the application period, the researchers took samples from the digestive tract of the fish and looked for relevant genetic changes in the gut bacteria.


"As expected, administration of the antibiotic induced an increase in the genes responsible for resistance to that antibiotic," said COMI doctoral student Johan Sebastian Sáenz Medina, lead author of the paper.


"One example are genes for pump proteins, which simply remove the active substance from the bacteria again. However, we were particularly surprised by the different mechanisms that we could detect by which antibiotic resistance genes are spread amongst gut bacteria of the fish," Medina added. "This suggests that the bacteria also exchange resistance through viruses, known as phages, and transposons."


Further metagenomic studies confirmed that these mobile genetic elements induce a fast distribution of resistance genes among genomes of different organisms. So far, it has been postulated that only plasmids (in essence, easily transferable mini-chromosomes) are mainly responsible for the exchange of resistance genes.


"The finding that resistance is also extensively transferred between bacteria without the involvement of plasmids is really quite surprising," Dr. Schloter commented.


"Based on this observation, relevant dissemination models should be reviewed and modified. In addition, our data certainly lead us to question whether and to what extent we should continue to use antibiotics in the world's increasing number of aquaculture."


- Helmholtz Zentrum München / Science Daily