Objective: To investigate the effects of PM2.5 exposure on susceptibility to Klebsiella infection and bacterial clearance, and to discuss its possible mechanisms.
Methods: Eighty-six healthy male SD rats were randomly divided into 4 groups: a control group, a Klebsiella pneumoniae infection group(infection group), a PM2.5 group and a PM2.5+ Klebsiella pneumoniae infection group (combined group) .We developed a rat model in which the animals were given Klebsiella pneumoniae, PM2.5 exposure and PM2.5 exposure followed by infection with Klebsiella pneumoniae respectively. The clinical scores were evaluated. The total mortality of each group was assessed. Bacterial load in the BALF was quantified and the infection rate of each group was assessed.Lung histopathological changes were detected by HE staining. The concentrations of IL-6 and TNF-α in serum were detected by ELISA. Cells in the BALF were counted for each group by microscopy. The changes of tracheal membrane epithelial cells were observed by scanning electron microscope.
Results: The total mortality in the combined group (n = 14) was higher than that in the control group (n = 0), infection group(n = 4) and PM2.5 group(n = 4). The infected cases in the combined infection group (n = 13) was higher than that in the infection group (n = 6). The total number of WBC in BALF in the combined group on the first day[(11.96 ± 0.56)×10(5)/L] and seventh day [(15.68 ± 0.81)×10(5)/L] was higher than that in the control group, the infection group and the PM2.5 group. The neutrophil number in BALF in the combined group on the first day[(5.76 ± 0.44)×10(5)/L] and seventh day [(9.41 ± 0.64)×10(5)/L] was higher than that in the control group, the infection group and the PM2.5 group. The lung pathological changes were much more severe in the combined group as compared to those in the control, the infection and the PM2.5 groups. Concentrations of TNF-α in serum in the combined group on the first day [(829 ± 90) ng/L] and the seventh day [(1055 ± 91) ng/L] were higher than those in the control group and the PM2.5 group. Concentrations of IL-6 in serum in the combined group on the first day [(1.26 ± 0.16) ng/L] and seventh day [(1.95 ± 0.18) ng/L] was higher than those in the control, the infection and the PM2.5 groups. Tracheal cilia in the PM2.5 group showed signs of disorderly arrangement, adhesion and ecclasis.
Conclusions: PM2.5 exposure increased the susceptibility of the rats to Klebsiella pneumoniae infection and decreased bacterial clearance.Its mechanism may be related to impairment of the bronchial mucociliary system and interaction of cytokines.