InfectoGnostics researchers at the Leibniz Institute for Photonic Technology (Leibniz IPHT) in Jena, Germany, have characterized a new bacterial strain that combines genetic properties from multiple strains. The pathogen belongs to the methicillin-resistant staphylococci (MRSA) and contains another special resistance gene that can be mobilized and spread via bacteriophages – viruses that kill bacteria. The results of the analysis were published in the journal Frontiers in Genetics in November 2021 (DOI: 10.3389/fgene.2021.723958).

During the screening of a seriously ill patient in Regensburg in 2014, a bacterial strain was isolated that stood out due to unusual genetic properties and could not be assigned to any already known MRSA strain. Researchers from the Department of „Optical-Molecular Diagnostics and Systems Technology“ at the Leibniz IPHT in Jena were recently able to show through a characterization of the conspicuous strain that hybrids of different bacterial strains could be more common than previously assumed and that bacteriophages also play a role in the transmission of resistance genes.

Resistance to key antibiotic

„We have completely sequenced the pathogen and found that an unusually large gene segment of one particular Staphylococcus aureus strain has inserted itself directly into the genome of another. This has created a kind of ‚genetic mosaic‘ that combines both disease-causing factors and several resistance genes in one MRSA strain,“ explains the lead author of the paper, Sindy Burgold-Voigt, a PhD student at Leibniz IPHT. Such a „mosaic genome“ is quite unusual in bacteria of the S. aureus species, according to the scientists, as the doctoral student goes on to explain: „The nuclear genome of staphylococci was previously considered to be very constant and resistant to change. A huge DNA insertion that, as here, accounts for almost a third of the total genetic material, was previously unknown.“

The newly inserted gene section brings with it a so-called „gene cassette“ that also confers antibiotic resistance typical of MRSA. But the part that forms the „backbone“ of the mosaic strain also has, in turn, an additional resistance gene called dfrG, which makes it resistant to the antibiotic trimethoprim. This agent is classified as an „essential drug“ by the World Health Organization and is used in particular for bladder infections or to treat specific lung infections in AIDS patients.

Phages can spread resistance genes between bacterial strains

Bacteriophages could play a special role in the spread of such resistance genes: These are viruses that specifically attack bacteria, multiply with and in the bacteria, and ultimately either destroy the bacterium or become embedded in its genetic information. In the process, phages first introduce their genetic material into the bacterial DNA as so-called „prophages“.

Such a transfer of bacterial genes via phages has so far been a rather rarely observed mechanism, as Sindy Burgold-Voigt explains: „Until now, the focus of infection research has mostly been on gene transfer via mobile genetic elements such as plasmids and transposons. In the case of the MRSA strain analyzed, however, a clinically highly relevant resistance gene was now located on a prophage. Since bacteriophages can in principle also package genes from adjacent or distant sections of the bacterial genome in their protein coat, this mechanism probably also contributes generally to the spread of antibiotic resistance.“

In the image above:
Scientist Sindy Burgold-Voigt (Leibniz IPHT) prepares a bacterial culture in the laboratory at the InfectoGnostics research campus in Jena.