Monitoring cystic fibrosis airway infections with Pseudomonas aeruginosa with anti-OprF serum antibodies

Background: The management of cystic fibrosis (CF) requires knowledge of the patient's microbiological status. The serology of anti-Pseudomonas aeruginosa antibodies against exoenzymes or water-soluble antigens has gained diagnostic value, particularly to detect the onset of colonization with P. aeruginosa. However, the diversity and variable expression of these antigens, which was unknown when the ELISAs became common diagnostic procedures at CF clinics, prohibits the quantitative evaluation of bacterial antigen load during intermittent and chronic infection. Methods: An ELISA was developed to measure the serum IgG antibody levels against P. aeruginosa porin OprF, a species-specific, conserved, immunogenic and constitutively expressed protein present in the outer membrane and extracellular vesicles. Results: Serial serum samples were collected from 310 people with CF (pwCF) over a period of up to 15 years. Compared to a reference of P. aeruginosa - negative CF sera set to 1, OprF antibody titers ranged from 0.3 to 13.2 (median: 1.7) in 56 intermittently colonized patients and from 0.5 to 51.2 (median: 11.8) in 176 chronically colonized pwCF showing higher anti-OprF antibody levels during chronic than during intermittent colonization with P. aeruginosa (P = 0, Z = - 21.7, effect size 0.62). Inhalation with twice daily 80 mg tobramycin decreased OprF antibody titers (P = 5 x 10-5), particularly during the third and fourth year of chronic colonization. Conclusion: The OprF ELISA should be an appropriate tool to monitor Pseudomonas serology at all stages of infection and disease severity and to study the impact of short- and long-term therapeutic interventions.