A canine model of Pseudomonas aeruginosa ventilator-associated pneumonia using a defined bacterial inoculum

Introduction

This prospective pilot study set out to develop an animal model of Pseudomonas aeruginosa that would be suitable for the application of molecular techniques to evaluate virulence in which instillation of a reference strain of P. aeruginosa results in a monoculture ventilator-associated pneumonia. For this purpose, male adult greyhounds were used in an animal research laboratory.

Methods

The animals were anaesthetised, orally intubated and mechanically ventilated. An inoculum of P. aeruginosa (strain PA01) was instilled into the oropharynx at 1 hour and 8 hours post-intubation. The animals were terminated at 78 hours.

Results

Pneumonia was evaluated based on macroscopic grading and microbiological (bacterial count) findings. We were able to maintain anaesthetic, haemodynamic and respiratory support for the study duration of 78 hours. A monobacterial pulmonary infection was established in four out of five animals. Administration of ceftriaxone 1 g daily effectively suppressed all other bacteria. This allowed proliferation of the single strain P. aeruginosa (PA01) we had inoculated with no culture of other organisms.

Conclusion

Over a short period of time we were able to reproduce a monoculture ventilator-associated pneumonia in a significant percentage of animals. We successfully developed an animal ICU model that we were able to sustain for 78 hours. This canine model of P. aeruginosa (PA01) ventilator-associated pneumonia is suitable for the application of molecular techniques such as signature-tagged mutagenesis, differential fluorescence induction, and in vivo expression technology.