Removing a key metabolite called pyruvate from Pseudomonas aeruginosa and Staphylococcus aureus bacteria biofilms — two of the most common bacteria found in cystic fibrosis (CF) patients — could help boost the effectiveness of antibiotics, a study reports.
The study, “Pyruvate-depleting conditions induce biofilm dispersion and enhance the efficacy of antibiotics in killing biofilms in vitro and in vivo,” was published in the journal Nature Scientific Reports.
Biofilms are communities of microorganisms composed of a matrix of polymers that include proteins, sugars, fats, and genetic material secreted by the microbes. They allow bacteria to attach and grow, and protect them from the action of antibiotics.
Biofilms are considered a cause of many chronic infections, such as the recurrent lung infections in CF patients whose lung environment promotes biofilm formation. Disrupting biofilms could represent an easier and more effective treatment for such infections.
Because pyruvate, the end product of a metabolic cellular process called glycolysis, can impair the initial formation of biofilms, researchers decided to test whether removing pyruvate would have an impact on biofilm maintenance and dispersion of bacteria.
Bacteria surface attachment is a multi-step process where the final step, called dispersion, is a regulated process by which bacteria escape biofilm status, and transition to the free-living mode of growth — known as planktonic mode.
To test their hypothesis, researchers used an enzyme called pyruvate dehydrogenase (PDH) that degrades pyruvate into other molecules.
They observed that P. aeruginosa bacteria in biofilms treated with PDH were reduced by up to 2.9 log (by about 794 times) with increasing concentrations of the enzyme. A similar observation was made with S. aureus biofilms.
Researchers then tested whether molecules that fuel PDH activity, such as NAD+ and CoA cofactors, could play a role in biofilm maintenance, and saw that providing these molecules alone had no effect.
They observed instead that the loss of biofilm mass was actually due to bacteria dispersion from their niche-grown colonies — 60 percent of microcolonies in pyruvate-depleted biofilms showed signs of dispersion.
“Overall, our findings suggest exposure of biofilms to PDH and thus, pyruvate-depleting conditions, to coincide with dispersion events,” the researchers said, suggesting that “pyruvate depletion enhances dispersion.”
Because previous studies showed that bacteria in the dispersion phase are more susceptible to antimicrobial action, the researchers then treated P. aeruginosa biofilms with the antibiotic tobramycin (150 micrograms per milliliter), both in the absence and presence of PDH.
Results showed that treatment with tobramycin together with PDH improved antibiotic efficiency by 2.4 log (251 times more efficient) than the antibiotic alone.
Next, the team tested whether this combined treatment could work on real infections. They used a pig burn wound model, with wounds infected with P. aeruginosa bacteria. Treatment with both tobramycin and PDH again led to a decrease of 2 logs (100 times) in bacteria in biofilm, compared with wounds treated with PDH alone, and by 4 logs (10,000 times) compared with untreated wounds.
The team also tested silver sulfadiazine (SSD), which has been the standard therapy for burn wound treatment in clinics for many years, and compared it to the PDH-tobramycin combined treatment. Results showed that the combined therapy was 2 logs (100 times) more effective than SSD in reducing the wounds’ biofilm population.
“Our findings strongly suggest the management of pyruvate availability to be a promising strategy to combat biofilm-related infections by two principal pathogens associated with wound and cystic fibrosis lung infections,” the researchers concluded.