A 14-year-old with cystic fibrosis is chronically colonized with a mucoid strain of Pseudomonas aeruginosa. During a routine clinic visit while he is stable, his pulmonologist considers adding a long-term oral medication to his regimen. Which class of medication has been shown to decrease the frequency of pulmonary exacerbations in this patient population by altering bacterial virulence properties rather than by direct bactericidal activity?