Macrolide therapy in Pseudomonas aeruginosa infections causes uL4 ribosomal protein mutations leading to high-level resistance

Abstract

Background: Cystic fibrosis (CF) patients have reduced mucociliary clearance resulting in recurring and chronic bacterial lung infections. Pseudomonas aeruginosa is one of the most common pathogens to colonize the airways of CF patients and can persist in the lungs for decades. CF patients infected with P. aeruginosa are treated with macrolides to inhibit quorum sensing, mucoidity and has additional immunomodulatory effects. However, according to the EUCAST committee, P. aeruginosa is not susceptible to macrolides leaving resistance mechanisms largely overlooked. Methods: Using a modified susceptibility testing protocol, P. aeruginosa isolates harbouring a mutated uL4 ribosomal protein were tested for resistance against macrolide antibiotics. Quorum sensing related properties, alterations in proteome composition and ribosome subunits distribution were further analysed to characterize the effect of the uL4 mutations on the physiology of the bacteria. Findings: Several uL4 mutations were identified in isolates from P. aeruginosa collections from various sources and geographical locations. Most of them mapped to the conserved loop region of uL4 and resulted in increased survival upon macrolide exposure. uL4 mutations did not negatively impact the physiology of the bacteria and greater concentrations of antibiotic were needed to inhibit the growth, reduce swimming motility, and induce redox sensitivity. Proteome analysis revealed that pathways involved in ribosome adaptation displayed altered expression levels possibly to compensate for the uL4 mutations, which changed the subunit distribution of the ribosome. Interpretation: Macrolides used against P. aeruginosa cause selection of macrolide resistant mutants which is a widespread - but uncharacterized - phenomenon. Using a modified susceptibility test, revealed that macrolides are indeed effective bacteriostatic antibiotics against P. aeruginosa and that this effect - along with macrolide-induced quorum sensing modulation - are drastically reduced in uL4 mutants. Macrolide antibiotics should, therefore, be considered as active antimicrobial agents against P. aeruginosa and resistance development should be contemplated especially when patients are treated with prolonged courses of macrolides.

Preserving the efficacy of antibiotics to tackle antibiotic resistance

“…Importantly, azithromycin resistance mutations have been described to be selected for in clinical strains of P. aeruginosa chronically infecting the lungs of these patients. Then, although P. aeruginosa is considered intrinsically resistant to macrolides in vitro, this class of antibiotics exerts a selective pressure within infection conditions (Goltermann et al., 2022, 2024).…”

Persistent Bacterial Infections, Antibiotic Treatment Failure, and Microbial Adaptive Evolution

“…(Figure 1) [9]. These complicating factors explain why persistent infections are often thought to require aggressive treatment with combinations of antibiotics in the clinic, and why treatment of apparently antibiotic sensitive bacterial populations fails to eradicate the bacteria [10]. Continuous unsuccessful antibiotic treatment will eventually result in genetically determined resistance-not only of the targeted infecting bacteria, but also of commensal bacterial populations residing in other organs and tissues of the patient [11].…”