Mucoid <i>Staphylococcus aureus</i>: A Clinical Trial of Its Prevalence and Association with Lung Function in People with Cystic Fibrosis.

Abstract

<b>Rationale:</b> The mucoid phenotype of <i>Staphylococcus aureus</i> is caused by adaptation. Excessive biofilm formation associated with a protective effect for mucoid <i>S. aureus</i> was observed in isolates from respiratory samples of people with cystic fibrosis (pwCF). <b>Objectives:</b> There is little knowledge about the prevalence of mucoid <i>S. aureus</i> in pwCF and a potential association with CF lung disease. <b>Methods:</b> A prospective multicenter study was conducted (cross-sectional and longitudinal). Specimens and case report forms were sent to the central study laboratory for characterization of <i>S. aureus</i> and analysis of clinical parameters. <b>Measurements and Main Results:</b> In the cross-sectional study, in 41 (9.1%) of 451 <i>S. aureus</i>-positive pwCF from 13 CF centers, mucoid <i>S. aureus</i> was cultured. In the longitudinal study, the distribution of <i>CFTR</i> genotypes and the number of pwCF with highly effective modulator therapy and coinfection with <i>Pseudomonas aeruginosa</i> were equivalent in the mucoid group (35 pwCF) versus the control group (only nonmucoid <i>S. aureus</i>; 36 pwCF). Although lung function did not differ between groups as a whole, a subgroup analysis revealed significantly worse lung function for female pwCF with mucoid <i>S. aureus</i> as well as for pwCF if <i>P. aeruginosa</i> coinfection was excluded. <b>Conclusions:</b> In the era of highly effective modulator therapy, worse lung function was associated with female and <i>P. aeruginosa</i>-negative pwCF with mucoid <i>S. aureus</i> compared with pwCF with only nonmucoid <i>S. aureus</i>. Therefore, appropriate culture conditions should be established to detect mucoid <i>S. aureus</i>. Further investigations are needed to elucidate the relationship between mucoid <i>S. aureus</i> and CF lung disease. Clinical trial registered with www.clinicaltrials.gov (NCT04171583).