Acid aspiration induces bacterial pneumonia by enhanced bacterial adherence in mice

Area of Science:

• Pulmonary Medicine
• Microbiology
• Pathophysiology

Background:

• Respiratory aspiration of gastric contents is a risk factor for developing bacterial pneumonia.
• The precise mechanisms by which acid aspiration contributes to pneumonia severity are not fully understood.
• Pseudomonas aeruginosa is a common opportunistic pathogen implicated in hospital-acquired pneumonia.

Purpose of the Study:

• To investigate if acid aspiration enhances bacterial adherence of Pseudomonas aeruginosa to the tracheal epithelium.
• To determine the impact of acid aspiration and P. aeruginosa co-challenge on mouse survival and bacterial lung burden.
• To elucidate the role of acid-induced airway injury in the pathogenesis of bacterial pneumonia.

Main Methods:

• Mice were intratracheally challenged with varying concentrations of hydrochloric acid (HCl) and/or a sublethal dose of P. aeruginosa.
• Survival rates and bacterial counts in lung tissues were assessed.
• Bacterial adherence to the tracheal epithelium was visualized and quantified using scanning electron microscopy.

Main Results:

• A 10(-1) N concentration of HCl, when combined with P. aeruginosa, significantly increased lung bacterial numbers and reduced survival.
• Mice receiving only HCl (at tested concentrations) or P. aeruginosa survived.
• Concentrated HCl (10(-1) N) significantly enhanced P. aeruginosa adherence to the tracheal epithelium compared to lower concentrations or saline.

Conclusions:

• Acid aspiration, particularly at higher concentrations, causes airway epithelial injury.
• This injury enhances the adherence of Pseudomonas aeruginosa to the damaged epithelium.
• Enhanced bacterial adherence is a key factor in the development of bacterial pneumonia following acid aspiration, potentially explaining severe cases in patients.