Characterisation of mucoid Staphylococcus aureus recovered from the airways of cystic fibrosis patients: prevalence, impact on clinical course and detailed analysis by molecular and imaging techniques

• Applicant: Professorin Dr. Barbara C. Kahl
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens ; Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2017 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391496579

S. aureus is one of the first isolated pathogens recovered from the airways of CF patients. In many patients, S. aureus persists for decades in spite of antibiotic treatment and host defence. During persistence in the airways, S. aureus needs to adapt to this hostile niche. Just recently we described mucoid S. aureus isolates as a so far not reported phenotype recovered from the airways of CF patients. These mucoid isolates carried a 5bp-deletion in the intergenic icaR-icaA region of the ica-operon leading to hyper-expression of biofilm. So far, neither the prevalence of mucoid S. aureus nor the impact on lung disease in CF patients is known. Furthermore, a detailed analysis of the performance of mucoid S. aureus within the airways (e.g. anaerobic conditions, the interaction with P. aeruginosa mucoid/non-mucoid, spatial analysis in sputum as an ex vivo specimen) is not clear. Moreover, the underlying mechanism of mucoid S. aureus isolates without a 5bp-deletion as recently described, which were also isolated from our CF patients, is not clear and will be further characterised.Therefore, in our proposal we plan to perform (1.) a clinical part of the project to determine the prevalence of mucoid S. aureus isolates in a cross-sectional study and the impact of identified mucoid S. aureus on the clinical course of the lung disease by observing patients with mucoid S. aureus for 12 months in comparison with a group of age-, gender- and P. aeruginosa-positive/negative matched group of S. aureus-positive patients without mucoid isolates. In the second part of our project we plan to characterise (2.) the performance of mucoid S. aureus isolates within the airways under different environmental conditions in vitro (aerobic versus anaerobic), which mimic the in vivo situation in the CF lung habitat in terms of biofilm formation, interaction with host cells and host defence. Furthermore, (3.) we plan to investigate the underlying mechanisms of mucoid isolates, for which we could not detect a 5bp-deletion in the icaR-icaA intergenic region using next generation sequencing and RNA-seq analysis. Lastly, (4.) we plan to use a new visualisation technique named MiPACT, which allows to characterise the interaction of mucoid/non-mucoid S. aureus with host cells and other important CF pathogens such as P. aeruginosa in sputa from CF patients as ex vivo specimens.

• DFG Programme: Research Grants