Expression pattern of soluble triggering receptor expressed on myeloid cells-1 in mice with Acinetobacter baumannii colonization and infection in the lung

Abstract

Background: Acinetobacter baumannii (A. baumannii) is one of the most troublesome opportunistic pathogens associated with hospital-acquired pneumonia (HAP). It is important to be able to discriminate A. baumannii colonization from infection in its early stages so that effective antibiotics can be promptly applied.Recent studies have reported that the secretion of soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) is markedly upregulated in pneumonia and sepsis, but the expression pattern of sTREM-1 in A. baumannii colonization and infection in the lung has not been explored.Methods: C57BL/6J male mice were intraperitoneally injected with 1% streptozotocin for 5 consecutive days to establish diabetic models. Subsequently, aerosol inhalation of A. baumannii suspension was performed in these mice to induce pulmonary colonization or infection with saline as vehicle control. Mice were sacrificed and lung tissue was harvested on days 0, 1, 3, 5 and 7 after exposure. Pharyngeal swab culture, lung homogenate culture, and H&E staining of lung tissue were performed to assess the severity of infectious inflammation. sTREM-1 expressions in serum and lung supernatants, serum procalcitonin (PCT) and C-reactive protein (CRP) concentrations were measured by ELISA. Results: A. baumannii colonization and infection models were verified by pharyngeal swab culture, lung homogenate culture, and H&E staining. While sTREM-1 concentrations in mice with A. baumannii colonization remained unchanged in serum and lung supernatants, sTREM-1 expression levels in infected animals were significantly upregulated. In addition, serum sTREM-1 concentration was positively correlated with serum levels of PCT and CRP. Conclusions: Dynamic secretion of sTREM-1 is associated with the development of A. baumannii infection in the lung. Therefore, sTREM-1 expression level may be a promising biomarker for discriminating A. baumannii infection from colonization.

Utility of sTREM-1 biomarker and hcp Gene for Identification of Acinetobacter baumannii Colonization and Infection in Lung

“…Microbial culture, WBC count and classification, CRP, PCT, and temperature monitoring are used to distinguish infection from colonization. A new inflammatory marker, sTREM-1 ( 8 , 16 , 26 , 27 ), for identifying bacterial infection and colonization in experimental animals has recently been reported ( 2 ). The current study found sTREM-1 and PCT to be significantly higher in the infection relative to the colonization group on days 1 to 10 ( P < 0.05), demonstrating the potential utility of these two biomarkers.…”

“…All data were tested for normality and normally distributed data are expressed as mean ± standard deviation with differences between two independent samples tested by t test ( 2 ). Nonnormally distributed data are expressed as median (quartiles) (M [QL–QU]) and were tested using Mann-Whitney U test ( 17 ).…”

“…Z test was applied for comparison between ROC curves ( 6 ). P < 0.05 indicated that the difference was statistically significant ( 2 ) and SPSS (IBM SPSS Statistics 22.0) was used for data analyses ( 18 ).…”

“…Acinetobacter baumannii (Ab) is a gram-negative bacterium responsible for bacteremia, pneumonia, meningitis, and urinary tract infections in patients with impaired immune function ( 1 ). Acinetobacter baumannii is carried by up to 25% of healthy people with normal immune systems and accounts for approximately 20% of intensive care unit (ICU) infections worldwide ( 2 ). Lung Ab colonization, which occurs frequently insusceptible populations, is a prerequisite for infection ( 3 ).…”

“…Feng et al ( 8 ) demonstrated a positive correlation between serum sTREM-1 and sputum bacterial load. Hence, sTREM-1 in serum may have significance in identifying the infection or colonization of A. baumannii ( 2 ).…”