(CN) – In an effort to help combat one of the greatest current threats to public health, researchers report Thursday they have identified the molecular basis of a major antibiotic resistance transfer mechanism in bacteria.
Antibiotic resistance is aided by the transfer of transposons – also known as jumping DNA – which can move autonomously from one part of the genome to another. When transferred between pathogens, transposons can bring antibiotic-resistant genes with them.
In addition to determining how this process occurs, the researchers also developed molecules and a proof-of-principle for blocking such transfers. Their findings were published in the journal Cell.
“By shedding light on the molecular mechanisms that drive the transmission of antibiotic resistance determinants between bacterial cells, we can better understand the routes and requirements of drug resistance spreading,” lead author Orsolya Barabas told Courthouse News in an email.
“This will allow us to develop improved diagnostic and risk assessment approaches, and to design improved treatment procedures for antibiotic resistance colonized patients to prevent further transmission of resistance. In addition, this research can allow us to discover strategies to block resistance transfer, and our current study provides proof-of-principle for this.”
Methicillin-resistant staphylococcus (MRSA), extended spectrum beta-lactamase (ESBL) producing Enterobacteriaceae, vancomycin-resistant enterococcus (VRE), and other bacteria have developed resistance to most of the drug compounds used today.
“Bacteria can not only develop but also share their ability to resist treatment, and the excessive use of antibiotics worldwide is an important accelerator of the problem. In addition, research and development in the area of microbiology has been very limited in the last decades,” said Barabas, who is a researcher at the European Molecular Biology Laboratory.
“Our study illustrates how fundamental atomic-resolution insights into molecular mechanisms can advance health care procedures and technology in this area.”
Focusing on transposons and their molecular structure, the report offers the first crystal structure of a protein-DNA machine that inserts transposons, and the resistance they hold, in recipient bacteria.
The team found that the transposase protein, the workhorse of the transposon insertion mechanism, has an abnormal shape, which allows it to bind to the DNA in an active state. This prevents cleavage, and thus the elimination of, the transposon until it can transfer the antibiotic-resistance gene in the new host genome.
The protein’s unusual shape also requires the transposon DNA to unravel and open up, enabling it to deposit its payload of antibiotic resistance at many places in an extremely broad scope of bacteria.
“If you think of ropes or wires, they are usually bundled and wound-up to make them stronger. If you want to tear or cut one, it's much easier if you unwind and loosen it first,” Barabas said. “it's the same for DNA, and the transposon transfer mechanism takes advantage of this.”
The transposase protein first unravels and divides the transposon’s DNA strands, which makes it easier to transfer them in the new site in the recipient genome.
Based on the crystal structure, the team also developed molecules and a proof-of-principle for preventing the transposons’ movement.
“In the long term, this could help control the spread of antibiotic resistance genes,” Barabas said.
The researchers provide two methods for blocking this transfer which could, for example, disable resistance conveyance in individuals diagnosed as carriers of antibiotic-resistant bacteria.
The first strategy prevents the transposase protein from going to its activated conformation by barring its architecture with a newly designed peptide – a short chain of amino acids.
The second method is a DNA-mimic that attaches to the open site within the transposon, thus preventing the DNA strand replacement that is required for resistance transfer.
“As we believe these features are broadly present in these jumping DNA elements, but not in related cellular systems, they may be quite specific to transposons,” Barabas said. “This way, we can target only the bacteria we want, and not the many good bacteria in our bodies and the environment.”
Much work still needs to be done between demonstrating the molecular structure of resistance transfer machineries in vitro and future uses. This is why the team will now focus on improving our understanding of the transfer processes in real life and examining and further developing strategies to limit conveyance.
“Multi-drug resistant bacteria present one of the biggest current global health threats worldwide,” Barabas said. “They occur in high and growing levels in both high- and low-income countries.
“Besides compromising treatment of serious infections, they put the achievements of modern medicine that rely on the availability of effective antibacterial drugs (i.e. organ transplants, post-operative and cancer treatment) at elevated risk.”
The research was funded by the Federal Ministry of Education and Research of Germany (BMBF) in the framework of the European Union-financed Joint Programming Initiative on Antimicrobial Resistance (JPI-AMR).