Antibacterial Effects of Bicarbonate in Media Modified to Mimic Cystic Fibrosis Sputum.

Pongsiri Jaikumpun,Éva Pállinger,Orsolya Dobay,Kasidid Ruksakiet,Martin Steward,Zsolt Lohinai,Ákos Zsembery,Balázs Stercz

doi:10.3390/ijms21228614

Abstract

Cystic fibrosis (CF) is a hereditary disease caused by mutations in the gene encoding an epithelial anion channel. In CF, Cl− and HCO3− hyposecretion, together with mucin hypersecretion, leads to airway dehydration and production of viscous mucus. This habitat is ideal for colonization by pathogenic bacteria. We have recently demonstrated that HCO3− inhibits the growth and biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus when tested in laboratory culture media. Using the same bacteria our aim was to investigate the effects of HCO3− in artificial sputum medium (ASM), whose composition resembles CF mucus. Control ASM containing no NaHCO3 was incubated in ambient air (pH 7.4 or 8.0). ASM containing NaHCO3 (25 and 100 mM) was incubated in 5% CO2 (pH 7.4 and 8.0, respectively). Viable P. aeruginosa and S. aureus cells were counted by colony-forming unit assay and flow cytometry after 6 h and 17 h of incubation. Biofilm formation was assessed after 48 h. The data show that HCO3− significantly decreased viable cell counts and biofilm formation in a concentration-dependent manner. These effects were due neither to extracellular alkalinization nor to altered osmolarity. These results show that HCO3− exerts direct antibacterial and antibiofilm effects on prevalent CF bacteria.

Highlights

Cystic fibrosis (CF) is a genetic disease caused by mutations in the gene encoding cystic fibrosis transmembrane conductance regulator (CFTR) protein [1]
We used a customized artificial sputum medium to investigate the effects of HCO3− on growth and biofilm formation by CF-related bacteria
We found that (i) HCO3− inhibits the growth of both P. aeruginosa and S. aureus in a concentration-dependent manner, (ii) the inhibitory effects are probably related to bacterial membrane damage induced by HCO3− and (iii) HCO3− inhibits biofilm formation by P. aeruginosa

Summary

Introduction

Cystic fibrosis (CF) is a genetic disease caused by mutations in the gene encoding cystic fibrosis transmembrane conductance regulator (CFTR) protein [1]. These functions are essential for regulating fluid movement across multiple epithelial surfaces in the body Mutations in this channel protein result in multiple-organ dysfunction, which profoundly affects the life expectancy of CF patients [5]. In the CF lung, CFTR dysfunction causes a decrease in Cl− and HCO3− secretion, and an increase in Na+ absorption, resulting in dehydration and acidification of the airway surface liquid (ASL). This abnormal ASL constantly hampers the mucociliary clearance mechanism (MCC) and compromises the immune defenses of the airways [6]. Since the eradication of bacterial biofilms is extremely difficult, chronic airway inflammation and lung damage frequently occur in CF [10]

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Results

Conclusion