Role of viable but non culturable cells in patients with cystic fibrosis in the era of highly effective modulator therapy

Background: Lung infections antibiotic treatment in Cystic Fibrosis patients (pwCF) is often complicated by bacterial persisters, including the so-called Viable but Non Culturable (VBNC) forms, live cells undetected by the routine cultural microbiological methods. This study investigated the occurrence of VBNC cells of five CF bacterial pathogens in 94 pwCF over one year and the possible associations with the patients' clinical features. Methods: Sputum samples, recovered at routine visits and during exacerbation episodes, were analyzed for the presence of the five pathogens by both routine culture-based assays and species-specific qPCR. VBNC cells were estimated as the difference between molecular and cultural counts and their presence was matched with the clinical data in particular the therapeutic regimens. Results: All but ten pwCF showed the presence of VBNC cells at least once during the study. Pseudomonas aeruginosa and methicillin-susceptible Staphylococcus aureus were the species most frequently found in the VBNC state. Only the former showed a significant association between chronic infection and VBNC cells presence; VBNC-MSSA positive patients significantly increased overtime. The presence of non culturable bacteria was generally concurrent with poor lung functionality and more frequent pulmonary exacerbations. No significant association with modulator treatment was evidenced. Conclusions: The obtained data demonstrated the overwhelming occurrence of bacterial VBNC cells in CF lung infections, warranting a constant monitoring of pwCF and underlining the need of implementing the routine culture-based assays with culture-independent techniques. This is pivotal to understand the CF bacterial population dynamics and to efficiently contrast the lung infection progression and worsening.