Inoculation Pneumonia Caused by Coagulase Negative .

Rationale: Although frequently retrieved in tracheal secretions of critically ill patients on mechanical ventilation, the existence of pneumonia caused by coagulase-negative staphylococci (CoNS) remains controversial.

Objective: To assess whether () inoculated in mice's trachea can infect normal lung parenchyma, increasing concentrations of were intratracheally administered in 221 immunocompetent mice.

Methods: Each animal received intratracheally phosphate-buffered saline (PBS) ( = 43) or live ( = 141) or inactivated ( = 37) at increasing load: 1.0 × 10, 1.0 × 10, and 1.0 × 10 colony forming units (CFU). Forty-three animals were sacrificed at 12 h and 178 were sacrificed at 36 h; 64 served for post-mortem lung histology, 157 served for pre-mortem bronchoalveolar lavage (BAL) analysis, and 42 served for post-mortem quantitative bacteriology of lung tissue. The distribution of biofilm-associated genes was investigated in the strain used in our experiment as well as among 19 other clinical strains collected from hospitals or nursing houses.

Measurements And Main Results: Intratracheal inoculation of 1.0 × 10 CFU live caused macroscopic and histological confluent pneumonia with significant increase in BAL white cell count, tumor necrosis factor-α (TNF-α), and macrophage inflammatory protein (MIP)-2. At 12 h, high concentrations of were identified in BAL. At 36 h, lung injury and BAL inflammation were less severe than at 12 h and moderate concentrations of species belonging to the oropharyngeal flora were identified in lung tissue. The inoculation of 1.0 × 10 and 1.0 × 10 CFU live caused histologic interstitial pneumonia and moderate BAL inflammation. Similar results were observed after inoculation of inactivated . Moreover, biofilm formation was a common phenotype in isolates. The low prevalence of the operon in our clinical strain collection indicated and independent-biofilm formation.

Conclusion: In immunocompetent spontaneously breathing mice, inoculation of causes concentration-dependent lung infection that spontaneously recovers over time. and independent biofilm formation is a common phenotype in isolates.