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Background: Staphylococcus aureus is one of the most frequently isolated pathogens in the respiratory tract of CF patients. Recently, we characterized peculiar mucoid S. aureus isolates, which are excessive biofilm formers and which carried a 5bp-deletion within the intergenic region of the ica operon. In this prospective study, we determined the prevalence of mucoid S. aureus-isolates in the airways of CF-patients during a 3-months period., Methods: We analyzed specimens (sputa, throat swabs) from 81 CF patients who attended two CF centers in Münster, Germany. Ten S. aureus isolates were randomly picked from every S. aureus-positive airway specimen and evaluated for mucoidy using Congo Red agar and phenotypic tests. Mucoid isolates were characterized by spa sequence typing, biofilm production and sequencing of the intergenic region of the ica operon to screen for the 5bp-deletion., Results: In 7 of 81 examined patients (8.6%), we detected mucoid S. aureus phenotypes (37 out of 1050 isolates; 3.5%). Twenty-five mucoid isolates carried the 5bp-deletion. Mucoid isolates produced excessive biofilm and were significantly more resistant to certain antibiotics., Conclusions: In our prospective study, mucoid S. aureus was present in 8.6% of S. aureus-positive CF-patients. In 6 of 7 patients, mucoid isolates carried the 5bp-deletion, indicating that also other so far not identified mechanisms cause excessive biofilm formation. Further studies are necessary to ascertain the clinical impact of mucoid S. aureus phenotypes on the severity of the CF disease., (Copyright © 2019. Published by Elsevier GmbH.)

Background: Cystic fibrosis (CF) is an autosomal recessive disease associated with chronic airway infections by Staphylococcus aureus as one of the earliest and most prevalent pathogens. We conducted a retrospective study to determine the S. aureus infection status of CF patients treated since 1994 at two certified CF-centres in Münster, Germany, to get insights into the dynamics of S. aureus airway infection and the clinical impact on lung function on a long-term perspective., Materials and Methods: We used data from our microbiological database collected between 1994 and 2016 for patients treated at two centres in Münster, Germany, respectively, to determine the infection status for S. aureus. Furthermore, the resistance to selected antibiotics was determined for all patients' isolates and for 15 patients on a longitudinal basis. In addition, the prevalence of adaptive phenotypes such as small colony variants (SCVs) and mucoid S. aureus was assessed., Results: For this study, 2867 patient years with respiratory specimens (mean of 9.3 years for every patient, range 1-22 years) were evaluated for 283 CF patients (median age of 7 years at the beginning of the observation period, range 0-57 years, 51% male). 18% of patients were rarely infected by S. aureus (≤24% of observation years), 20% of patients intermittently (25-49%) and 61% persistently (≥50% of observation period). Susceptibility testing for 12969 S. aureus isolates resulted in resistance to methicillin in 9%, trimethoprim/sulfamethoxazole in 10%, levofloxacin in 14%, gentamicin in 20%, erythromycin and/or clindamycin in 30% and penicillin in 80% of all isolates. S. aureus isolates of 15 patients revealed dynamics of resistance with increase, decrease and loss of resistant isolates to the analysed antibiotics during the study period. SCVs were isolated at least once from 42% (n = 118) of patients and mucoid isolates from 2% (n = 7) of patients. In the last study year, 89 patients were infected by S. aureus only, 44 patients by S. aureus and Pseudomonas aeruginosa and 18 by P. aeruginosa only. Patients infected by S. aureus only were younger and had better lung function compared to the other two groups., Conclusions: We determined a high percentage of patients with persistent S. aureus infection. During persistence, mostly fluctuation of resistance against various antibiotics was observed in the isolates indicating acquisition and loss of resistance genes by S. aureus. The prevalence of adaptive phenotypes during long-term persistence was high for SCVs (42% of patients), but low for mucoid isolates (2% of patients), which might be underestimated for mucoid phenotypes due to the retrospective study design and the difficulty to detect mucoid isolates in primary cultures. While patients with S. aureus only had better lung function and were younger, no difference was found between the group of P. aeruginosa and S. aureus co-infection and P. aeruginosa only with previous S. aureus infection., (Copyright © 2018 Elsevier GmbH. All rights reserved.)