An international research team from the Veterinary Medical University in Vienna, Austria (Vetmeduni Vienna) discovered a new mechanism for persistence of the bacterial pathogen Staphylococcus aureus.

Vetmeduni Vienna said the finding is of "great relevance as S. aureus is not only the best known but also one of the most dangerous multi-drug-resistant hospital germs for humans. This new bacterial route to persistence has been first described in a dairy cow with a long-lasting, chronic udder infection with implications for animal welfare, food safety and milk yield."

Staphylococci are common bacteria of the human and animal skin, the university announced, noting that S. aureus is a problematic species that can be harmful not only for people but can also be a major cause of mastitis infections in dairy cows. Common consequences are long-lasting and recurrent infections during which the bacteria constantly refine their properties and adapt to the host, the announcement said.

In a recent study at Vetmeduni Vienna funded by the Austrian Science Fund, an international team of researchers led by Tom Grunert investigated the adaptation of S. aureus within the host animal over the course of three months in a naturally infected dairy cow with chronic subclinical mastitis.

The analysis of the bacterial genomes revealed a complete replacement of the original bacterial strain by another genetic variant that was caused by an adaptation through mutation and selection.

Bacterial in-host evolution

This study was the first to observe a genetic and phenotypical adaptation of S. aureus within its bovine host, Vetmeduni Vienna said.

Helene Marbach, with the functional microbiology unit at Vetmeduni Vienna, said, “The mutation in the bacterial genome involves, in particular, only a single base exchange in a gene. The newly evolved clone exhibits strong changes in infection-relevant phenotypes such as higher proteolytic activity and biofilm formation.”

The researchers were able to demonstrate an alternative new mechanism for the persistence of S. aureus leading away from intracellular toward extracellular persistence, the announcement said.

The article “Within-host Evolution of Bovine Staphylococcus Aureus Selects for a SigB-Deficient Pathotype Characterized by Reduced Virulence but Enhanced Proteolytic Activity & Biofilm Formation,” by Helene Marbach, Katharina Mayer, Claus Vogl, Jean Y.H. Lee, Ian R. Monk, Daniel O. Sordelli, Fernanda R. Buzzola, Monika Ehling-Schulz and Tom Grunert, was published in Scientific Reports.

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