Pseudomonas aeruginosa grows as biofilms in the lungs of patients with cystic fibrosis (CF) but it remains unclear if the bacteria persist because the biofilms are antibiotic-resistant or if resistant variants are selected by antimicrobial therapy itself. In April 18 Nature, Eliana Drenkard and Frederick Ausubel of Harvard Medical School show that Pseudomonas biofilm formation and antibiotic resistance are linked to phenotypic variation and are switched on together.

Drenkard & Ausubel observed that antibiotic resistant phenotypic variants of P. aeruginosa with enhanced ability to form biofilms arise at high frequency both in vitro and in the lungs of CF patients. They also identified a regulatory protein (PvrR) that controls the conversion between antibiotic-resistant and antibiotic-susceptible forms (Nature 2002, 416:740-743).

"Drenkard and Ausubel have described a general mechanism — environment driven phenotypic switching — that explains how antibiotic-resistant biofilm variants of P. aeruginosa arise," wrote George O'Toole of...

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