Elevated glucose increases methicillin-resistant Staphylococcus aureus antibiotic tolerance in a cystic fibrosis airway epithelial cell infection model

TL;DR

High glucose levels in the airway of cystic fibrosis patients may make staph infections harder to treat with antibiotics.

Contribution

This study shows hyperglycemia increases antibiotic resistance in methicillin-resistant Staphylococcus aureus during CF airway infections.

Findings

Hyperglycemia increases S. aureus aggregation and antibiotic resistance in CF airway epithelial cell models.

Glucose restriction reduces bacterial aggregation and antibiotic resistance to normal levels.

Elevated glucose in airway surface liquid mimics conditions seen in CF and hyperglycemic patients.

Abstract

In a healthy lung, the airway epithelium regulates glucose transport to maintain low glucose concentrations in the airway surface liquid (ASL). However, hyperglycemia and chronic lung diseases, such as cystic fibrosis (CF), can result in increased glucose in bronchial aspirates. People with CF are also at increased risk of lung infections caused by bacterial pathogens, including methicillin-resistant Staphylococcus aureus. Yet, it is not known how increased airway glucose availability affects bacteria in chronic CF lung infections or impacts treatment outcomes.

To model the CF airways, we cultured immortalized CF (CFBE41o-) and non-CF (16HBE) human bronchial epithelial cells at air liquid interface (ALI). Glucose concentrations in the basolateral media were maintained at 5.5 mM or 12.5 mM, to mimic a normal and hyperglycemic milieu respectively. 2-deoxyglucose was added to high glucose culture media to restrict glucose availability. We collected ASL, basolateral media, and RNA from ALI cultures to assess the effects of elevated glucose. We also inoculated S. aureus onto the apical surface of normal or high glucose ALI cultures and observed the results of antibiotic treatment post-inoculation. S. aureus growth was measured by enumerating viable colony forming units (CFU) and with fluorescence microscopy. The effects of elevated glucose on in vitro growth and antibiotic treatment were also evaluated in standard bacterial culture medium and synthetic CF medium (SCFM).

We found that glucose concentrations in the ASL of ALI cultures maintained in normal or high glucose mimicked levels measured in breath condensate assays from people with CF and hyperglycemia. Additionally, we found hyperglycemia increased S. aureus aggregation and antibiotic resistance during infection of cells maintained in high glucose compared to normal glucose conditions. Heightened antibiotic tolerance or resistance as not observed during in vitro growth with elevated glucose. Limiting glucose with 2-deoxyglucose both decreased aggregation and reduced antibiotic resistance back to levels comparable to non-hyperglycemic conditions.

These data indicate hyperglycemia alters S. aureus growth during infection and may reduce efficacy of antibiotic treatment. Glucose restriction is a potential option that could be explored to limit bacterial growth and improve treatment outcomes in chronic airway infections.

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