Acid aspiration provokes the pneumonia caused by multidrug-resistant Acinetobacter baumannii in BALB/c mice

Abstract

Objective: To determine whether acid aspiration provokes the development of multidrug-resistant Acinetobacter baumannii (MDRAB) pneumonia in its host.

Methods: Groups of mice were inoculated intratracheally (IT) with 50 μl of 0.1N HCl and 1 × 10(8) colony-forming units (CFU) Ab396 (A+Ab group), or 50 μl of 0.1N HCl and 20 μl of 0.9% saline (A+S group), or 20 μl of 0.9% saline and 1 × 10(8) CFU of Ab396 (S+Ab group), or 50 μl of 0.9% saline and 20 μl of 0.9% saline (S+S group). Cytokines, bacterial loads in the bronchoalveolar lavage fluid (BALF), lung permeability, histopathology of the lungs, and survival rates were evaluated.

Results: Only the A+Ab mice developed extensive Ab396 pneumonia and had significantly elevated bacterial loads, increased lung leakage, and lower levels of tumor necrosis factor alpha (TNF-α) compared with the other three groups (p<0.05, Mann-Whitney U-test). Moreover, a strong synergistic effect (p<0.05, two-way analysis of variance) was observed between the acid induction and Ab396 infection, resulting in lung injury and an unfavorable survival outcome.

Conclusions: Lung injury caused by acid aspiration provoked secondary MDRAB pneumonia; also synergistic effects between acid aspiration and Ab396 infection resulted in a detrimental outcome in the infected mice.