AUTHOR=Shi Meng-meng , Monsel Antoine , Rouby Jean-Jacques , Xu Yan-ping , Zhu Ying-gang , Qu Jie-ming 

TITLE=Inoculation Pneumonia Caused by Coagulase Negative Staphylococcus

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.02198

DOI=10.3389/fmicb.2019.02198

ISSN=1664-302X

ABSTRACT=<sec><title>Rationale</title><p>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.</p></sec><sec><title>Objective</title><p>To assess whether <italic>Staphylococcus haemolyticus</italic> (<italic>S. haemolyticus</italic>) inoculated in mice’s trachea can infect normal lung parenchyma, increasing concentrations of <italic>S. haemolyticus</italic> were intratracheally administered in 221 immunocompetent mice.</p></sec><sec><title>Methods</title><p>Each animal received intratracheally phosphate-buffered saline (PBS) (<italic>n</italic> = 43) or live (<italic>n</italic> = 141) or inactivated (<italic>n</italic> = 37) <italic>S. haemolyticus</italic> at increasing load: 1.0 × 10<sup>6</sup>, 1.0 × 10<sup>7</sup>, and 1.0 × 10<sup>8</sup> 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 <italic>S. haemolyticus</italic> strain used in our <italic>in vivo</italic> experiment as well as among 19 other clinical <italic>S. haemolyticus</italic> strains collected from hospitals or nursing houses.</p></sec><sec><title>Measurements and Main Results</title><p>Intratracheal inoculation of 1.0 × 10<sup>8</sup> CFU live <italic>S. haemolyticus</italic> 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 <italic>S. haemolyticus</italic> 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<sup>6</sup> and 1.0 × 10<sup>7</sup> CFU live <italic>S. haemolyticus</italic> caused histologic interstitial pneumonia and moderate BAL inflammation. Similar results were observed after inoculation of inactivated <italic>S. haemolyticus</italic>. Moreover, biofilm formation was a common phenotype in <italic>S. haemolyticus</italic> isolates. The low prevalence of the <italic>ica</italic> operon in our clinical <italic>S. haemolyticus</italic> strain collection indicated <italic>icaA</italic> and <italic>icaD</italic> independent-biofilm formation.</p></sec><sec><title>Conclusion</title><p>In immunocompetent spontaneously breathing mice, inoculation of <italic>S. haemolyticus</italic> causes concentration-dependent lung infection that spontaneously recovers over time. <italic>icaA</italic> and <italic>icaD</italic> independent biofilm formation is a common phenotype in <italic>S. haemolyticus</italic> isolates.</p></sec>