Pongsiri Jaikumpun, Department of Oral Biology, Semmelweis university, Budapest, Hungary
Kasidid Ruksakiet, Department of Oral Biology, Semmelweis university, Budapest, Hungary
Introduction: Cystic fibrosis (CF) is caused by mutations in the gene encoding a cAMP-dependent epithelial anion channel which allows chloride and bicarbonate transport. In CF, impaired bicarbonate secretion leads to acidic airway surface liquid (ASL), thickening of mucus and defective elimination of bacteria. In fact, Pseudomonas aeruginosa (PA) and Staphylococcus aureus (SA) are commonly isolated from CF airways. These bacteria are mainly responsible for CF-related chronic lung disease. The artificial sputum medium (ASM) has been formulated to mimic the special environment in CF airways in vitro.
Aim: To test the effects of bicarbonate and different pH values on the growth of PA and SA in ASM.
Methods: ASM was prepared with or without bicarbonate. Media without bicarbonate were set to different pH values (6.5, 7.5 and 8.5). All bicarbonate-containing media (25, 50, 100 mM NaHCO3) were set to pH 7.5. Two strains of PA (ATCC and BIK17808) and SA (ATCC29213 and EM/11-3) were grown overnight in sterile ASM without bicarbonate (pH 7.5). Then equal amounts of bacterial suspensions were inoculated into different ASM in 96-wells plate in quadruplicate, and incubated at 37°C. The growth of bacteria was assessed with optical density measurements at 595 nm following 6 and 24 h.
Results: In the absence of bicarbonate, PA growth was independent of ASM pH whereas SA growth was ASM pH-dependent. Bicarbonate-containing media (25, 50, 100 mM) inhibited significantly the growth of all bacteria assessed after 6 h of incubation. However, following 24 h of incubation no difference in bacterial growth was observed in the presence and absence of bicarbonate.
Conclusion: Bicarbonate has bacteriostatic rather than bactericidal effect on PA and SA in media similar to the environment revealed in CF airways.
Doctoral School: Clinical Medicine
Program: Dental Research
Supervisors: Dr. Ákos Zsembery, Dr. Zsolt Lohinai, Dr. Orsolya Dobay
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