Researchers discovered that the airways of patients with cystic fibrosis (CF) often harbor diverse polymicrobial communities that likely affect the clinical response to antimicrobial therapy, according to a new study published in The ISME Journal.

The cornerstone of managing infections is through the administration of antimicrobial agents; the same is true for infections occurring in the airways of patients with CF. Patients with CF are particularly vulnerable to infection due to the overproduction of nutrient-rich mucilaginous secretions in the airways, and studies have indicated that antimicrobial therapy is often unsuccessful in wiping out the colonizing microorganisms.

The authors of the study set out to investigate the effects of 3 clinically relevant, species-specific antimicrobials (colistin, fusidic acid, and fluconazole) on steady-set polymicrobial populations containing Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans. They hypothesized that the 3 species-specific antimicrobials would have lower activity against their target microorganisms in polymicrobial cultures than in single-species cultures.

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To conduct their study, they collected the 3 bacterial/fungal species and conducted studies on them. The researchers discovered that growth in a polymicrobial environment was protective of the target microorganism from the effects of the antimicrobial agent introduced. The decrease in antimicrobial efficacy had both nonheritable and heritable components.

In addition, they discovered that species-specific antimicrobial interventions may have unintended and unpredictable results on the dynamics of microbial species that are not primary targets of the medication. For example, antimicrobial compounds that target non-P aeruginosa species may offer a selective advantage to P aeruginosa present in airways. This can complicate future treatment regimens and worsen patient prognosis.

“We show here that growth as a steady-state planktonic polymicrobial community can enhance the resistance of the inhabitants to antimicrobial agents, sometimes, by several orders of magnitude,” O’Brien and colleagues concluded.


O’Brien TJ, Figueroa W, Welch M. Decreased efficacy of antimicrobial agents in a polymicrobial environmentISME J. Published online March 19, 2022. doi:10.1038/s41396-022-01218-7