Inoculation Pneumonia Caused by Coagulase Negative Staphylococcus

Area of Science:

• Microbiology
• Infectious Diseases
• Pulmonary Medicine

Background:

• The role of coagulase-negative staphylococci (CoNS) in causing pneumonia, particularly in mechanically ventilated patients, remains debated.
• Staphylococcus haemolyticus is frequently found in respiratory secretions, but its pathogenic potential in the lungs is not well-established.

Purpose of the Study:

• To investigate the capacity of Staphylococcus haemolyticus to infect lung parenchyma in a mouse model.
• To determine the dose-dependent effects and resolution of Staphylococcus haemolyticus-induced lung infection.

Main Methods:

• Immunocompetent mice were intratracheally inoculated with varying concentrations of live or inactivated Staphylococcus haemolyticus or phosphate-buffered saline (PBS).
• Animals were analyzed at 12 and 36 hours post-inoculation, with assessments including bronchoalveolar lavage (BAL) analysis, lung histology, and quantitative bacteriology.
• Biofilm-associated gene distribution was examined in the experimental strain and other clinical isolates.

Main Results:

• High-dose (1.0 × 10^8 CFU) live Staphylococcus haemolyticus induced macroscopic and histological pneumonia with increased inflammatory markers in BAL fluid.
• Lung injury and inflammation decreased by 36 hours, with the emergence of oropharyngeal flora in lung tissue, suggesting resolution.
• Lower doses and inactivated bacteria also caused interstitial pneumonia and BAL inflammation, while biofilm formation was common and independent of the ica operon.

Conclusions:

• Staphylococcus haemolyticus can cause a concentration-dependent lung infection in immunocompetent mice that resolves spontaneously.
• Biofilm formation in Staphylococcus haemolyticus is a common phenotype, often independent of the icaA and icaD genes.