Vancomycin may not be able to treat MRSA infections for long Premium

Researchers have found Staphylococcus aureus can adapt to vancomycin while overcoming its fitness cost, threatening the long-term use of vancomycin in the clinic.

Antimicrobial resistance is one of the great crises of the 21st century, and Staphylococcus aureus is an important bacteria species leading this charge.

In 2019, for example, methicillin-resistant Staphylococcus aureus (MRSA) — a strain that can resist several antibiotics — was responsible for more than 100,000 deaths. Fortunately it is still significantly vulnerable to vancomycin, which has been doctors’ first-line treatment against MRSA infections for 40 years.

MRSA rarely resists vancomycin. Only 16 such cases have been reported in India so far. This is because when S. aureus acquires vancomycin resistance (to become VRSA), it also grows slower and is less fit.

Now, researchers have found S. aureus can adapt to vancomycin while overcoming this fitness cost. The study, published in the journal PLoS Pathogenson August 29, reported results threatening the long-term use of vancomycin in the clinic.

“Vancomycin has been reliable for treating MRSA for decades as it is very rare that S. aureus becomes resistant to vancomycin,” Eric Wright, a researcher at the University of Pittsburgh and study co-author, wrotein an email. “Our study shows that we may not be able to treat MRSA with vancomycin forever.”

All documented cases of VRSA are due to the transfer of a cluster of genes, called the vanA operon, from another vancomycin-resistant bacterium to S. aureus during a simultaneous infection. The researchers isolated VRSA strains from clinical samples and grew four of them carrying the vanA operon in the presence or absence of vancomycin.

First, they grew VRSA in the presence of vancomycin in both solid and liquid culture conditions to study different fitness parameters. Most strains of VRSA cultured under both conditions grew more slowly than S. aureus that was still susceptible to vancomycin, confirming that acquiring antibiotic resistance came with a fitness cost.