Effect of hyperglycaemia on the growth of lung pathogens in Artificial Sputum Media

Abstract

Elevated glucose concentration in the airway surface liquid due to high blood glucose (hyperglycaemia) has been associated with the increased risk of developing pulmonary infection. It has recently been shown that lungs are colonisedby resident bacteria and are not truly sterile. Several chronic lung conditions, such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), have been shown to induce changes in this bacterial population.Here we sought to develop an in vitro model using artificial sputum media (ASM) to investigate the effect of hyperglycaemia on Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA), two of the most common pathogens in CF patients.SA (ATCC29213) and PA (H174) were grown in the artificial sputum media (ASM) at varying glucose concentrations. Approximately 3×105 bacteria were added to 15 mL ASM and grown at 37°C with constant shaking. Two‐way ANOVA with Geisser‐Greenhouse correction and Pearsons correlation coefficients were used for statistical analysis.ASM supplemented with 4 mM glucose had a significant effect on the growth rate of both S. aureus and P. aeruginosa when compared with ASM with no glucose (p = 0.0028, n=5 for SA and p < 0.0001, n=5 for PA). Compared with growth in Mueller Hinton broth, only P. aeruginosa exhibited increased growth rate in the presence of 4 mM glucose (p = 0.0082, n = 3). Growth of both, S. aureus and P. aeruginosa, was correlated with the depletion of glucose in the media (p = 0.0002, n=5 for PA and 0.0038, n=5 for SA). The production of lactate by S. aureus was not related to the depletion of glucose as concentrations for both reached zero at the sixth hour of growth.As ASM mimics the nutrients available in the lungs, it facilitates the study of lung pathogens in the presence of glucose. The established in vitro assay in this study can be further utilised to examine the competition and/or co‐existence between multiple pathogens that are known to reside within the lungs.Support or Funding InformationResearch funded by MRC‐DTP